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Met Mailbag

Part of what makes working at NBC Weather Plus so fun is the ability to listen in when a Meterologist explains why certain weather phenomenon are happening, or recalls covering a big weather outbreak. What makes it more fun is the ability to follow up with questions generated from everyday life around the forecasting set.

Now, you have the chance to jump in and do the same thing. Have a question about the weather? Send your emails to the Met Mailbag at Weatherplus.com. Every other Thursday a Weather Plus Meterologist will answer a few of your best queries on the NBC Weather Pulse blog.

All you have to do is click on this link and send in your question. Make sure to put your name and hometown, and check the NBC Weather Pulse blog to see if your question is answered!

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This Week's Met Mailbag

Met Mailbag is your chance to have a Weather Plus Meteorologist answer your weather question. Every other Thursday, our NBC Weather Pulse Blog will publish the answers to questions you send us. This week's question was answered by NBC Weather Plus meteorologist Jackie Meretsky.

Question: What causes fog?
Submitted by D. Allen, Chicago, Illinois

Answer: Residents of the beautiful Island of Newfoundland (originally called Terra Nova) are no strangers to fog. In fact, the foggiest place in the world is the Grand Banks off Newfoundland where the warm gulf stream meets up with the cold Labrador current from the north.

Across the continental U.S., we have some very foggy regions as well, namely Charleston, West Virginia because of the terrain and air flow patterns, and San Francisco. Coastal cities out West have night and evening fog which can continue well through the morning's commute.

PHOTOS: Classic Fog Snapshots

Quite simply, fog is a cloud at the ground level and typically occurs when relative humidity at the ground level reaches 100%. It has many of the same properties as the cumulus and stratus clouds we see up above, but the formation is different.

WATCH: Click here to watch Jackie's on-air answer

Similar to the clouds in the sky, fog is made up of condensed water droplets but with sky clouds, air particles rise, cool and expand. Air particles cool in fog as well, but for different reasons and with different consequences. For example, rain can moisten and cool the air at the ground level until fog forms. Or, sometimes a warm and moist air mass coming in contact or moving over a colder surface (sometimes snow) can cause a type of fog called advection fog.

Fog is still fog in higher elevations as long as it comes in contact with the hilltop or mountain ridge. There are actually over a dozen types of fog - it all depends on how the cooling that caused the condensation occurred.

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Past Mailbags

April 5, 2007 | 1:45 p.m. ET

Question: What is the difference between a flood and a flash flood?
Submitted by Carrie O., Alexandria, Virginia

Answer: Hi, Carrie, and thanks for the timely question.

Spring is when we typically see the worst river flooding. On the other hand, summer is when we typically experience the worst flash flooding.

WATCH: Click here to watch Bill's on-air answer

A flash flood warning occurs within six hours of a rain even, or after a dam or levee failure. There is often very little preparation time for flash flooding and slow-moving thunderstorms are the biggest culprit of flash flooding.

A flood warning occurs on rivers and streams when prolonged rainfall over several days, or intense rain over short time, occurs. Melting snow and heavy rain cause most of the issued flood warnings.

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March 15, 2007 | 2:15 p.m. ET

Met Mailbag is your chance to have a Weather Plus Meteorologist answer your weather question. Each Thursday, our NBC Weather Pulse Blog will publish the answers to questions you send us. This week's question was answered by NBC Weather Plus meteorologist Kristen Cornett.

Question: Can Thunder Occur Without Lightning?
Submitted by M. Ritland, Huxley, Iowa

Answer: Thanks for the great question!

Thunder can never occur without lightning. Thunder is a direct result of the lightning itself.

See, the temperature of a lightning bolt is 30-50 thousand degrees.

When that bolt heats the air around it at such a rapid pace, the air expands causing a shock wave which we hear as thunder.

Click here to watch Kristen's on-air answer.

If you are close to the lightning, you'll hear it as a sharp crack while if you are farther away, it sounds more like a rumble.

Thanks again for your question!

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Met Mailbag (Gary Archibald, Weathercaster)

February 22, 2007 | 2:15 p.m. ET

Question: What causes the seasons?
Submitted by J. B., Parma, Ohio

Answer: Thanks for the great question J.B.!

Seasonal change results primarily from the Earth's axis of rotation tilting to its orbital plane. The angle of deviation is approximately 23.5 degrees. At any point during the summer or winter seasons, one part of the planet is more directly exposed to the sun's rays. As the Earth revolves around its orbit, this exposure alternates.

Because the direction of the Earth's tilt changes in relation to the Sun, the northern and southern halves of our planet get differing amounts of sunlight over the course of the year. In the Northern Hemisphere of the Earth, the axis points most toward the Sun in June. Because the Earth is leaning toward the Sun, it receives direct rays of sunlight and is warmer. On the other hand, the Earth's axis points most away from the Sun in December.

Because the Earth is leaning away from the sun, it receives the least amount of direct rays of sunlight and is cooler. Note, at any point in time, no matter what the season, the northern and southern hemispheres experience opposite seasons. For example, if the northern hemisphere is in winter then correspondingly, the southern hemisphere is in summer.

Thanks again for your question!

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Met Mailbag (Jeff Ranieri, Meteorologist)

February 15, 2007 | 2:00 p.m. ET

Met Mailbag is your chance to have a Weather Plus Meteorologist answer your weather question. Each Thursday, our NBC Weather Pulse Blog will publish the answers to questions you send us. This week's questions were answered by NBC Weather Plus Meteorologist Jeff Ranieri

Question: What is ice fog?
Submitted by Al Hurvitz, San Francisco, Calif.

Answer: Al, Since you're from California I’m sure you are a fog expert on many levels but the reason why you may not know about ice fog has a lot to do with the temperatures.

Ice fog is generally formed in higher elevations or a region that is super cold. Just like with ground fog… temperature, a moisture source, and calm winds are all key factors. Ice fog forms when the temperature is minus 30 F and below. So, with super cold temperatures the moisture freezes into ice particles at the lower levels.

WATCH: Click here to watch the on-air answer.

So if you want to actually see the ice fog on something other than your computer, a trip to the poles may be your only way to catch a glimpse!

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Met Mailbag (Kristen Cornett, Meteorologist)

February 8, 2007 | 2:15 p.m. ET

Question: Is it true that it's more likely to snow the closer the temperature is to 32 degrees F?
Submitted by Jack D., Hoboken, N.J.

Answer: Well Jack, whether or not it’s going to snow is a lot more complicated than the air temperature that we measure here on the ground.

You have to think of the atmosphere in layers. If the temperature is at or below freezing from the cloud all the way down to the ground, then precipitation will fall in the form of snow. It can still snow, however, if the temperature at the surface is above freezing as long as the other layers of the atmosphere are cold enough. In that case, the snow usually just melts after it hits the ground, as long as the temperature of whatever the snow lands on is below freezing too.

WATCH: Click here to watch the on-air answer.

Here is where it gets a little more complicated. Sometimes, the temperature at the surface is below freezing and we get freezing rain or sleet instead of snow. The reason for this is that there is warm layer of air above the surface which causes the falling snow to melt. Once the snow melts in that warm layer, it can re-freeze again as it passes through the freezing temperatures close to the ground. If it’s a narrow layer of cold air at the surface, freezing rain is the result. If the layer of cold air at the surface is a little thicker, sleet results.

Met Mailbag (Bill Karins, Meteorologist)

February 1, 2007 | 1:40 p.m. ET

Question: What classifies a snowstorm as a blizzard?
Submitted by Jodi Blumberg, Seattle, Wash.

Answer: Good question Jodi.

Lets discuss what the difference is between a snowstorm and a blizzard. A snowstorm is when a large area is affected by accumulating snow. A blizzard is when blinding snow and ferocious winds affect an area for an extended period of time.

To be called a blizzard, two things have to happen for three straight hours, the winds must top 35 mph -and- the visibility must be measured at a 1/4 mile or less.

The biggest misconception is that one to two feet of snow is called a blizzard. Without strong winds for 3 straight hours it's just a powerful snowstorm.

Thanks for the question!

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Met Mailbag (NBC Weather Plus Meteorologists)

January 25, 2007 | 2:54 p.m. ET

Question: What is thunder snow?
Submitted by Matt Gold, Santa Monica, California

Answer:I hope you were able to witness the snow that fell last week in the mountains above Malibu! I find California to be an extraordinary state because of its meteorological diversity. From exploring the vineyards in Napa Valley, to skiing in Tahoe or just watching the sunset form the Santa Monica pier, California provides one of the most picturesque backdrops in the world.

Since you live in California, you probably don’t see thunder snow too often, if ever. This phenomenon is more common with lake-effect snow generated across the Great Lakes in the Midwest. One of the last recorded instances of thunder snow in your home state was in the Sierra Nevadas in November 2000.

Think of thunder snow as a thunderstorm with snow falling instead of rain. The main component is that strong upward motion within the cold sector of an extra tropical cyclone. This normally occurs between fall and spring when surface temperatures are near the freezing mark. Your best chance at seeing and hearing thunder snow is in March.

This can happen in three ways:

Cold air pushing across milder lake water which we call lake effect snow. The main factors with this type of thunder snow are wind shear and a steepened lapse rate between the temperature aloft and the lake water temperature. To put it another way, Mother Nature does not take temperature clashes well and often responds with dramatic results which we witness when the seasons change.

A thunderstorm that either forms in a winter environment or one which runs into cool air and produces snow.

A large scale snowstorm in the comma head (northwest side) of an extra tropical cyclone with strong vertical mixing producing lightning and thunder. In some cases, thunder snow is found underneath a trough of warm air aloft (a trowal).

VIDEO: Click Here To View The On-Air Met Mailbag Answer

Thunder snow differs from a typical thunderstorm not just because of the precipitation, but because of the relationship between the snow and the thunder in that it suppresses the thunder acoustically. So, you can only hear the thunder within a two to three kilometer radius, which only further limits your chances of hearing this unique phenomenon.

Thanks for the question Matt!

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Met Mailbag (Gary Archibald, Weathercaster)

January 18, 2007 | 12:45 p.m. ET

Question: What makes a storm an ice storm instead of snowstorm?
Submitted by B. Ritland, Story City, Iowa

Click to enlarge

Answer: Thanks for sending in the question about one of the most treacherous types of winter storms!

A few ingredients are required for an ice storm to form. First, a moist, warm layer of buoyant air must sustain itself over a region of colder air lying at the surface.

IMAGES: Icy Branches

Second, ground level temperatures must maintain a steady, freezing or sub-freezing value. Precipitation in the form of snow, ice pellets, or sleet will then fall from clouds above into the warm layer of air and essentially melt into water particles. The water vapor or droplets that result freeze on contact as they fall further still onto the terrain and all surrounding objects.

That's why in an ice storm, anywhere from a fraction of an inch to several inches can form on trees and power lines and coat roads. Ice storms in general can be dangerous to entire communities because of the potential to impede or make travel dangerous on the ground and in the air, cause widespread damage to property, and cause major power outages.

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Met Mailbag (Kristen Cornett, Meteorologist)

January 11, 2007 | 11:45 a.m. ET

AP Photo/Stillwater News Press, Stephen Holman

Question: Is there such a thing as 'tornado season'? If so, when is it?
Submitted by Steve Tice, Mobile, Ala.

Answer: Tornado season is the period where we typically or historically see the most tornado activity in a particular area as it varies from region to region.

SLIDESHOW: Tornadoes

We tend to see the majority of tornado activity in the U.S. from late winter into mid summer. There is a general northward shift in the season during this time.

VIDEO: Click Here For Video Met Mailbag Answer

The peak period in the Southern Plains is during May and early June but on the Gulf Coast where you are Steve, it is earlier during the spring. In the northern plains and upper midwest, it is June or July. It is very important to remember though, tornadoes can and have occurred any time of the year as long as the conditions are right!

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Met Mailbag (Jeff Ranieri, Meteorologist)

December 21, 2006 | 9:00 a.m. ET

Met Mailbag is your chance to have a Weather Plus Meteorologist answer your weather question. Each Thursday, our NBC Weather Pulse Blog will publish the answers to questions you send us. This week's questions were answered by NBC Weather Plus Meteorologist Jeff Ranieri

Question: What was the last year without a hurricane hitting the U.S. mainland?
Submitted by Larry Aronberg, Lake Worth, Fla.

Answer: Larry, after our very busy season in 2005 and then our quiet season in 2006 this is super timely and the answer may have been lingering right in the back of your brain.

Larry, as you remember 2005 was record-breaking on many accounts and then came 2006, which was unusually quiet even after predictions of a busy season. This past year we had not only El Nino conditions slow the season, but also the theory of African dust playing into decreased activity. With both of these factors, this past season of 2006 was actually the last hurricane season with no U.S. land falling hurricanes. 2006 finished out with 9 total storms and two of these becoming major hurricanes, this included Helene and Gordon.

Before this season, 2000 and 2001 both went without a hurricane hitting the mainland.

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Met Mailbag (Weather Plus Meteorologists)

December 14, 2006 |6:07 p.m. ET

Question: What are sun dogs?
Submitted by Jamie Reese, Cleveland, Ohio

Answer: Sun dogs, also called mock suns, area pair of brightly colored spots on either side of the sun. They always appear 22 degrees on either side of the sun at the same elevation as the sun.

PHOTOS: Sun Dogs

They are formed when sunlight is bent as it passes through a very specific type of ice crystal in the air. These crystals, called plates, are six sided, or hexagonal and are very flat.

Click to watch the on-air answer.

Sun dogs form very similar to halos. The difference is the orientation of the ice crystals. If hexagonal crystals are oriented with their flat faces horizontal, a sundog will be observed...however it the hexagonal crystals are randomly oriented, a halo is observed.

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Met Mailbag (NBC Weather Plus Meteorologists)

November 16, 2006 | 4:06 p.m. ET

Question: Why does lightning occur?
Submitted by Tanya Platt, Chicago, Ill.

Answer: Tanya, thanks so much for your question.

Lightning is a high-current discharge of electricity. It occurs as the atmosphere tries to balance the positive and negative charges within a thunderstorm and the earth's surface.

When an object with a huge positive or negative charge gets close to an object carrying the opposite charge, a spark jumps across the space between them to neutralize the charges. In a thunderstorm that 'spark' is a lightning bolt.

INTERACTIVE: All About Lightning

The top of a thunderstorm cloud becomes positively charged, while the bottom becomes negatively charged. Static electricity builds up between the earth and the cloud and a spark, that we don't see, comes down out of the cloud. Just before that invisible bolt reaches the ground it's met with a positively charged spark that's moving upward. When these two collide an 'explosion' occurs as the return stroke travels up and the result is the visible flash we know as lightning.

Click here to watch Elise answer this question on-air.

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Met Mailbag (NBC Weather Plus Meteorologists)

November 09, 2006 | 12:00 p.m. ET

Question: How is wind chill calculated?
Submitted by Miriam F., Baltimore, Md.

Answer: Hello Miriam and thanks for the very timely question about wind chill!

It's only November, but with winter just around the corner and holiday decorations sneaking into the stores already, wind chill will be an all-too-familiar weather term you will hear from meteorologists before you know it.

Growing up in Toronto, Ontario Canada, I am no stranger to wind chill. As a youth, I remember my mother saying "the wind chill will be -20" on numerous occasions and admittedly I didn't really know what she was talking about, but I knew it was going to be VERY cold.

So what exactly is wind chill? Wind chill is the temperature felt on exposed skin as a result of the combination of temperature and wind speed. In simpler terms, it is really just how cold it feels to exposed skin. In very cold climates like the Arctic, as well as places with very high winds like Mount Washington in New Hampshire, wind chill is a critical concept.

Click for this week's on-air answer

Calculating wind chill is an entirely different animal. It's a complicated formula so to see what the formula is, you can go here and check out this handy graphic from the National Weather Service.

The basic premise is that as the air temperature falls, the chilling effect of a wind increases. The first wind chill calculations in the United States were developed during World War two. The calculations have been modified over the years to reflect it's affect on humans as opposed to animals and inanimate objects. The official calculation used presently is determined by iterating a model of skin termperature under various temperatures and wind speeds. But to make things simple for you, you can use this handy wind chill calculator on our website!

Thanks for the question!

To send a weather question to our Met Mailbag, click on this link, and check back next week to see if your question is answered!

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Met Mailbag (NBC Weather Plus Meteorologists)

November 2, 2006 | 2:45 p.m. ET

Question: Does weather affect fall foliage color?
Submitted by Eileen Anders, Bath, Maine.

Answer: Thank you for the question Eileen. Even though your leaves in beautiful Maine are mostly on the ground now, many locations around the country are still showing off their vibrant colors and the weather is affecting the show.

ALSO: Fall Foliage

If you want vivid colors you need to hope for sunny, cool days with no rain during the peak leaf season. This scientific term for this seasonal aging of the leaves is called SENESCENCE. Scientists have found that changing leaf colors are a stress reaction like fall’s less humid fall air and cooler temperatures.

Click for the on-air Met Mailbag answer

The key to the intensity of the color is the amount of stress on each tree. This is why the unhealthy trees peak and drop their leaves before the healthy trees around them do.

The duration of the peak leaves also depends on the weather. Most of New England lost its leaves because of the strong windstorm this past weekend. Heavy rain will also cause the leaves to drop prematurely.

MORE: Fall Foliage Guide

So Eileen, next year as fall arrives, you want to hope for a dry spell with cool sunny days to get the most out of those picturesque maple trees in Maine.

Thanks for the question!

To send a weather question to our Met Mailbag, click on this link, and check back next week to see if your question is answered!

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Met Mailbag (Kristen Cornett, NBC Weather Plus Meteorologist)

October 26, 2006 | 2:10 p.m. ET

Question: Does lake effect snow only happen over the Great Lakes? Submitted by Karen Angell, Royal Oak, Mich.

Answer: No Karen, the Great Lakes aren't the only lakes associated with lake-effect snow.

The definition of lake-effect snow is snow that results as cold air moves over a large expanse of warmer lake waters, picking up water vapor and dropping snow on the downwind shore of the lake.

While the most common and heaviest lake effect snows take place on the downwind shores of the Great Lakes, the southern and southeastern sides of the Great Salt Lake also receive significant lake-effect snow.

Click for the on-air Met Mailbag answer

Any large lake may produce lake-effect snow downwind if there is cold air moving across its warmer waters. A few other locations that experience this are the eastern shores of the Hudson Bay, Gulf of St. Lawrence and parts of Japan, Korea and Scandinavia.

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Met Mailbag (Jeff Ranieri, Meteorologist)

October 19, 2006 | 2:00 p.m. ET

Met Mailbag is your chance to have a Weather Plus Meteorologist answer your weather question. Each Thursday, our NBC Weather Pulse Blog will publish the answers to questions you send us. This week's questions were answered by NBC Weather Plus Meteorologist Jeff Ranieri

Question: I've heard of earthquake weather. What is it?
Submitted by Stacy Watson, Kansas City, Mo.

Answer: Earthquakes do involve a part of the earth and its energy, but as far as weather and its influence on earthquakes, there is no scientific evidence leading to this idea.

When I read your question Stacy I said no right away, but I did think back to school and remember some early ideas on this way back when...

It turns out your question is not entirely in left field. According to the USGS, back as far as the 4th century B.C., theorist often thought there was a connection with wind, where it would get trapped in deep pockets of the earth and cause the ground to shift.

Click for the on-air Met Mailbag answer

This later proved false as we learned through study that many earthquakes originate miles below the earth's surface, where temperature, rain and wind would have zero effect. So, the next time we have a large storm and there happens to be an earthquake you now know there is no relation.

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Met Mailbag (Elise Finch, Meteorologist)

October 12, 2006 | 12:17 p.m. ET

Question: What is wind shear and why does it affect flying
Submitted by Bobbi Willig, Glenside, Pa.

Answer: Thanks for the question Bobbi. Wind shear refers to the change in wind speed and/or wind direction between two points in the atmosphere. Depending on where those two points are, wind shear can be vertical or horizontal. Small amounts of wind shear are common and can be found from the top of the atmosphere to the ground. Larger values typically exist near fronts or the jet stream. Wind shear is an important factor in the determining the severity of thunderstorms.

When it comes to flying, wind shear is an issue because changes in wind speed and direction create swirls of air…and those swirls of air create turbulence. Turbulence can shake an airplane, no matter how big, and make a flight very uncomfortable and in some cases dangerous.

Click for the on-air Met Mailbag answer

Another concern if an aircraft experiences a sudden decrease in wind speed is that it can reduce the lift on its wings to dangerously low values. So people in the aviation field make it their business to know when large values of wind shear will be present along a flight paths.

To send a weather question to our Met Mailbag, click on this link, and check back next week to see if your question is answered!

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Met Mailbag (NBC Weather Plus Meteorologists)

October 05, 2006 | 1:30 p.m. ET

Question: What is an occluded front?
Submitted by Dennis Baranec of Naples, Florida.

Answer: Hi Dennis. Thanks for your question about occluded fronts. It's a very timely question since we are in that transitional time of year with all sorts of colors and fronts on our weather maps.

First of all, a front is simply the place where two air masses meet. It's almost like two people coming together for a tug of war. One will inevitably dominate or overtake the other.

Occluded fronts are formed when a cold front overtakes a warm front or a quasi-stationary front. The warm air is forced up once the two fronts collide and curve upwards. The point of curvature is called the triple point.

Click for the on-air Met Mailbag answer

Along an occluded front, thunderstorms are possible followed by a much drier air mass.

If you're looking for an occluded front on a weather map, look for the purple line with alternating half circles and triangles pointing in the direction of travel.

I hope that answers your question, Dennis.

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Met Mailbag (NBC Weather Plus Meteorologists)

September 28, 2006 | 2:30 p.m. ET

Met Mailbag is your chance to have a Weather Plus Meteorologist answer your weather question. Each Thursday, our NBC Weather Pulse Blog will publish the answers to questions you send us. This week's questions were answered by NBC Weather Plus Meteorologist Bill Karins.

Question: What makes a regular thunderstorm different from a tropical depression?
Submitted by Mike Shields, Greensboro, N.C.

Answer: Thanks for the question Mike. The key to understanding the difference is in the size and organization of these storms.

A thunderstorm is considered a small storm (a few miles wide), while a tropical depression can be a few hundred miles-wide. Both contain strong winds and heavy rain but another difference is the amount of lightning in the storms. Thunderstorms usually produce frequent lightning, but tropical systems do not. They lack the vertical winds to produce a lot of lightning.

Click for the on-air Met Mailbag answer

During the hurricane season we look at satellite maps to see where thunderstorms are popping up. If an area of thunderstorms can persists for a couple of days and then start to spin, a tropical depression can form. In many ways, tropical depressions are just a bunch of thunderstorms rotating around an area of low pressure.

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Met Mailbag (NBC Weather Plus Meteorologists)

September 21, 2006 | 3:44 p.m. ET

Met Mailbag is your chance to have a Weather Plus Meteorologist answer your weather question. Each Thursday, our NBC Weather Pulse Blog will publish the answers to questions you send us. This week's questions were answered by NBC Weather Plus Meteorologist Kristen Cornett.

Question: What is the difference between a typhoon and a hurricane?
Submitted by Britta Pressler, Eau Claire, Wis.

Answer: Thanks for the question, Britta.

There isn't much difference at all! Once a tropical cyclone reaches winds of 74mph, they become either a hurricane or typhoon. The terms are simply regionally specific.

Click for the on-air Met Mailbag answer

In the North Atlantic Ocean, the Northeast Pacific Ocean east of the dateline and the South Pacific Ocean east of 160E we call them "hurricanes."

In the Northwest Pacific Ocean west of the dateline, they are called "typhoons."

To send a weather question to our Met Mailbag, click on this link, and check back next week to see if your question is answered!

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Met Mailbag (NBC Weather Plus Meteorologists)

September 14, 2006 | 2:00 p.m. ET

Met Mailbag is your chance to have a Weather Plus Meteorologist answer your weather question. Each Thursday, our NBC Weather Pulse Blog will publish the answers to questions you send us. This week's questions were answered by NBC Weather Plus Meteorologist Jeff Ranieri.

Question: What are some tips on staying safe inside when there's a bad lightning storm?
Submitted by Tony Wilson, Ivanhoe, Ill.

Answer: Tony... What a great question!

AP Photo/Billings Gazette, David Grubbs

When a thunderstorm rolls through, staying inside is first and foremost the most important tip!

Also, be sure to stay away from doors and windows.

Do not take a shower or bath.

Make sure to turn off, unplug and stay away from electronics and appliances.

Click for the on-air Met Mailbag answer

Remember, if you are close enough to hear thunder you are close enough to get struck by lightning.

And finally, if you can't get inside, crouch down low as lightning tends to strike the highest object in its path.

Using these tips will help keep you much safer when the next thunderstorm rolls through your neighborhood.

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Met Mailbag (Elise Finch, Meteorologist)

September 7, 2006 | 2:17 p.m. ET

Question: I thought tropical storms were named in alphabetical order, but we've gone from Ernesto to John to Florence. Why is this? -- Dorothy Williams, Delaware

Answer: That's a great question, Dorothy, and I'm sure lots of other people were wondering the very same thing.

The National Hurricane Center names storms alphabetically and in spite of how it appeared, they didn't skip any letters or names. It just so happens that Ernesto, like our most recent storm Florence, is on one list, and John is on a different one.

These are the storm names to be used in this year's 2006 hurricane season in the Atlantic basin.

Each year there is a list of names set aside for storms that develop in the Atlantic Basin and a separate list for those that develop in the Pacific. In the Atlantic ... we had only had 4 named storms, so Ernesto was the name given to the 5th storm. When Florence formed Tuesday morning it became the 6th named storm of the Atlantic season.

So far this year the Pacific has been more active with 9 named storms which is why their latest storm was named John.

Click to watch this week's on-air answer.

Just so you know, the names are maintained and updated by an international committee of the World Meteorological Organization. Six lists are used in rotation which means the 2006 list will be used again in 2012 unless a storm is so deadly or costly that the future use of its name on a different storm would be inappropriate. In that case the WMO will strike the offending name and select a replacement at their annual meeting.

To send a weather question to our Met Mailbag, click on this link, and check back next week to see if your question is answered!

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Met Mailbag (NBC Weather Plus Meteorologists)

August 31, 2006 | 1:00 p.m. ET

Question: What is a waterspout?
Submitted by James Kim, Los Angeles, Calif.

Answer: James, thank you for the question! I like to think of a waterspout as Mother Nature's awesome display of tornadic activity when she feels like going for a swim.

Historic NWS Collection/NOAA

Waterspouts in the Bahamas Islands

Waterspouts are simply tornadoes over water, but they form differently to the tornadoes we see on land.

Click for the on-air Met Mailbag answer

Where can you commonly see waterspouts? In tropical areas where thundershowers occur frequently, like the Bahamas or around the Florida Keys.

If you're looking for a more meteorological explanation of this phenomenon then let me put it another way for you. A waterspout is an columnal vortex which looks like a funnel cloud and it is connected to a cumuliform cloud. Most waterspouts are "fair-weather" as they are not associated with a rotating updraft of a supercell thunderstorm.

In the Florida Keys alone, there are roughly 400 per year. Strong or tornadic waterspouts are associated with mesocyclones and are quite dangerous to ships, planes and swimmers.

To send a weather question to our Met Mailbag, click on this link, and check back next week to see if your question is answered!

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Met Mailbag (NBC Weather Plus Meteorologists)

August 24, 2006 | 2:35 p.m. ET

Question: Why is weather usually milder near the ocean?
Submitted by Joanne Gross, Chicago, Illinois.

Answer: Thanks for the wonderful question Joanne. It is usually milder near the ocean because water holds on to the heat a lot better than the land.

If you live on the ocean in a warm climate, this means the temperatures stay mild most of the time. On a hot summer day, the land warms up faster than the ocean water. This hot air then rises. In it's place, the mild air over the water rushes in over the land to replace it. This is called the sea breeze.

At night, just the opposite happens. The land cools off faster, so the air over the ocean rises and the mild, land air heads out to sea. This is called the land breeze.

Click for the on-air Met Mailbag answer

Because of this daily occurrence near any ocean Joanne, the temperatures near the water appear mild in the winter and not as hot in the summer.

Thanks for the question!

To send a weather question to our Met Mailbag, click on this link, and check back next week to see if your question is answered!

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Met Mailbag (Kristen Cornett, NBC Weather Plus Meteorologist)

August 17, 2006 | 1:30 p.m. ET

Question: What does it mean when meteorologists use the word "supercell" in reference to thunderstorms?
Submitted by Sara Peterson, Concord, Mass.

Answer: Great question, Sara. Well, a supercell is a type of thunderstorm that is the most rare and most dangerous to form.

Supercells have a rotating updraft, also called a mesocyclone.

They're long-lived and often produce tornadoes and large hail.

Click to view Kristen's on-air answer

Sometimes the rotation of the rising air makes the cloud look twisted.

These types of thunderstorms can form anywhere, but they are usually best viewed in the Plains states.

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Met Mailbag (NBC Weather Plus Meteorologists)

August 10, 2006 | 1:55 p.m. ET

Question: What is the jet stream?
Submitted by Margot B., Calif.

Answer: Well Margot, jet streams are fast-moving currents of air in the upper levels of the atmosphere.

These streams of air were once thought to be similar to jets of water...so they were named jet streams!

But it's probably better to think of them as relatively narrow rivers of air that flow in a wavelike manner about seven to eight miles above the earth's surface.

Jet streams are caused by temperature differences between air masses, which means that jet streams divide colder air to the north from warmer air to the south.

During the summer, for example, the mid-Atlantic jet is typically located in northern Canada.

That position allows warm air from the south to move north and warm things up.

During the winter months, the jet stream dives south and positions itself in the southern-most portion of the United States, which allows cold air from Canada to sink south.

Click here to watch Elise's on-air answer.

To send a weather question to our Met Mailbag, click on this link, and check back next week to see if your question is answered!

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Met Mailbag (Jackie Meretsky, NBC Weather Plus Meteorologist)

August 3, 2006 | 4:24 p.m. ET

Question: Why does humidity make it feel hotter?
Submitted By Carlos Roche, Temperance, Michigan

Answer: This is a very timely question considering the oppressive heat and humidity that is blanketing the East!

The reason humidity makes it feel hotter is it makes it harder for your body to expel heat. Believe it or not, your body naturally cools itself by sweating. Sweat in turn evaporates into the air. The warmer molecules in those sweat droplets evaporate first, leaving the cooler ones behind and, in turn, make you feel cooler.

However, if there is more moisture in the air, it's harder for water to evaporate, so it's harder to cool off, thus making you feel hotter.

Click to watch the on-air answer.

To send a weather question to our Met Mailbag, click on this link, and check back next week to see if your question is answered!

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Met Mailbag (Jeff Ranieri, NBC Weather Plus Meteorologist)

July 27, 2006 | 3:37 p.m. ET

Question: How does hail form?
Submitted By Alice Martin, Madison, Wisconsin

Alice, it is a complicated process that often has a painful ending.

Hail forms when you generally have a strong thunderstorm with very high clouds in the atmosphere.

There are updrafts and downdrafts in a storm. When rain is swept into the updraft of a thunderstorm it can be lifted into the upper atmosphere more than 50,000 feet in some cases.

As the rain travels this high it can reach temperatures below freezing. That is where the rain freezes, becoming what we know as hail.

It then begins to rapidly drop in the downdraft -- and if the air stays cool enough -- the stone will come to the ground still frozen.

There is a catch!

If it is a very turbulent storm, the hailstone may be swept back into a storm cloud several times making the hail larger and larger!

Alice -- I hope that answered your question!

Click to watch the on-air answer

To send a weather question to our Met Mailbag, click on this link, and check back next week to see if your question is answered!

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Met Mailbag (NBC Weather Plus Meteorologists)

July 20, 2006 | 2:30 p.m. ET

Met Mailbag is your chance to have a Weather Plus Meteorologist answer your weather question. Each week, our NBC Weather Pulse Blog will publish the answers to questions you send us. This week's question was answered by NBC Weather Plus Meteorologist Bill Karins.

Question: When you give the forecast of temperatures for a given area is that temperature in the sun or shade?
Submitted by Bill Phillips, La Habra, Calif.

Bill, I bet most people don’t know the answer to this and just how strictly the rules are for an accurate temperature.

All the temperatures we show you on a map are taken in the shade, but not under a tree.

A birdhouse-looking device is where all the temperatures around the country come from.

The rules say the temperature should be taken 6 feet off the ground in a ventilated white box, away from buildings and pavement.

To watch the video, please click the play icon in the video box to the right.

To send a weather question to our Met Mailbag, click on this link, and check back next week to see if your question is answered!

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Met Mailbag (Jackie Meretsky, NBC Weather Plus Meteorologist)

July 13, 2006 | 3:33 p.m. ET

Question: What makes the thunder noise?
Submitted by Joann Schraut Rollin, Hatboro, Pennsylvania.

Answer: Well Joann lightning, which accompanies thunder, is very hot and it heats the air to more than 50,000 degrees Fahrenheit.

That's hotter than the surface of the sun!

This intense heating causes the air to rapidly expand.

This creates a shockwave moving in all directions.The shock wave then becomes a sound wave and that is the thunder we hear.

Click to watch Jackie's on-air answer.

To send a weather question to our Met Mailbag, click on this link, and check back next week to see if your question is answered!

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Met Mailbag (NBC Weather Plus Meteorologists)

July 6, 2006 | 1:35 p.m. ET

Question: I would like to know about the recent floods. What if it was December and the temperature was 28 degrees outside? What would the precipitation totals be if it were snow instead of rain that fell in the flooded states?
Submitted by Bob Baker, Batesville, Arkansas.

Answer: Well Bob, cold air doesn't hold as much moisture as warm air. So the difference in precipitation totals doesn't translate that easily.

If it were 28 degrees outside, the air would not have been nearly as moist to start with. But generally speaking, one inch of rain equals 10 inches of snow.

Click for the on-air Met Mailbag answer

If it's a really dry snow though, totals could get as high as 20 inches while a really wet snow would be more like 5 inches.

Thanks for your question, Bob!

To send a weather question to our Met Mailbag, click on this link, and check back next week to see if your question is answered!

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Met Mailbag (NBC Weather Plus Meteorologists)

June 29, 2006 | 9:32 p.m. ET

Question: How does a hurricane form a double eye wall, and does this happen often?
Submitted by Jo Anna Gold, Whitehall, Ohio

Thanks for your question, Jo Anna.

A double eyewall occurs in about half of major hurricanes.

When hurricanes show a double eye-walled structure, they are often in the process of undergoing an "eye wall replacement cycle."

First, a concentrated ring of convection develops outside the eye wall. This ring then moves inward leading to a double-eye.

INTERACTIVE: Hurricanes 101

The inner eyewall will then dissipate while the outer one intensifies and moves inward.

The double-eye-walled structure usually marks the end of an episode of intensification and may last for a day or two.

For more information on hurricanes, check out Weather Plus Hurricane Central.

To send a weather question to our Met Mailbag, click on this link, and check back next week to see if your question is answered!

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Met Mailbag (NBC Weather Plus Meteorologists)

June 22, 2006 | 2:30 p.m. ET

Question: Is heat lightning different from the regular lightning I see during a thunderstorm?
Submitted by Michael Simonson, New York, NY.

I love this question, Michael because I love to dispel weather folklore and wives-tales.

Technically speaking, there is no such thing as heat lightning.

AP Photo/Sandusky Register, Abigail Bobrow

A bolt of lightning strikes, as seen from Bogart Road in Huron Township, Ohio, Wednesday, June 21, 2006.

It's actually plain-old lightning or even just the flash from the lightning that you are seeing.

Thunderstorms at night are more common during the summer. And after dark, the flashes from the lightning can be seen from miles away.

INTERACTIVE: Lightning Safety

It got the name "heat lightning" because it is hot where you are observing it and it's not raining -- hence heat lightning.

Next time you see lightning, go check out your local radar at weatherplus.com and I bet you will see a thunderstorm a few towns away.

Click here to watch Bill's on-air answer.

For more information on lightning and other forms of severe weather, check out our Severe Weather Page.

And don't feed bad about the question, Michael...I thought there was heat lightning until I took my first meteorology class in college.

To send a weather question to our Met Mailbag, click on this link, and check back next week to see if your question is answered!

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Met Mailbag (NBC Weather Plus Meteorologists)

June 15, 2006 | 2:15 p.m. ET

Question: Why isn't the summer solstice, when the sun is directly overhead, the hottest day of the year? Generally, it gets hotter in August.
Submitted by Nick Quinn, Southdale, Mich.

Click to enlarge

Answer: Good question, Nick... I used to wonder the same thing.

In the spring, the days are longer than the nights so more heat is arriving than leaving and the air becomes warmer.

But even after the summer solstice, which this year falls on June 21st, as the days get shorter, there is still more heat arriving than leaving.

This just adds to the heat already in place, resulting in temperatures that continue to rise. Nick Quinn, I hope that answers your question.

Click here for the on-air answer to this week's Met Mailbag question.

To send a weather question to our Met Mailbag, click on this link, and check back next week to see if your question is answered!

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Met Mailbag (NBC Weather Plus Meteorologists)

June 8, 2006 | 2:32 p.m. ET

Question: Is it true that if you count from when you see lightning until you hear thunder, you are as many miles from the lightning strike as the number of seconds you counted?
Submitted by Jennifer Lamarillo, Washington, D.C.

Well, Jennifer, that's sort of right.

AP Photo/Darren Hauck

Astraphobia, the fear of thunder and lightning, is probably the most common weather-related phobia.

Count the number of seconds between when you see lightning and hear the thunder. Then divide by 5. That will tell you how many miles away the lightning strike was.

For example, if 10 seconds elapse between the lightning and the thunder, divide 10 seconds by 5 and you get 2.

INTERACTIVE: Lightning Safety

The stroke was 2 miles away!

Click here to watch Bill's on-air answer.

For more information on lightning and other forms of severe weather, check out our Severe Weather Page.

To send a weather question to our Met Mailbag, click on this link, and check back next week to see if your question is answered!

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Met Mailbag (NBC Weather Plus Meteorologists)

June 1, 2006 | 2:20 p.m. ET

Question: We hear a lot about hurricanes in the Atlantic, but has a hurricane ever hit Hawaii or the West Coast of the United States?
Submitted by Doug Lomax, Irvine, Calif.

Answer: Great question, Doug -- and even better timing with this being the first day of the Atlantic Hurricane Season.

Actually, Hawaii has been devastated by one of the worst hurricanes in our country's history.

Hurricane Iniki struck in 1992 with Category 4 winds of 140 miles per hour, 18-foot waves and a 6-foot storm surge.

The final destruction was totaled at $2 billion and Iniki also took six lives while injuring more than 100.

California, on the other hand, is relatively safe from hurricanes because of the cold water just off the coast.

But back in 1939 a tropical storm did make it all the way to Long Beach, California.

So, Doug, it's possible -- but unlikely -- a hurricane will ever make it your way to Irvine.

Click here to watch Bill's on-air answer.

To send a weather question to our Met Mailbag, click on this link, and check back next week to see if your question is answered!

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Met Mailbag (NBC Weather Plus Meteorologists)

June 1, 2006 | 10:10 a.m. ET

Question: Who picks hurricane names? Do the same people pick the names in the Pacific, Atlantic, Indian Ocean, etc? Has there ever been a Hurricane Luis? -
Submitted By Luis Guillen, Jersey City, NJ

Answer: Well Luis, there was a Hurricane Luis. It was such a devastating storm that the name was retired and won't be used again. Luis was a category 4 storm that hit the northeasternmost of the Leeward Islands in the Carribbean in 1995, with an estimated sixteen dead and two-and-a-half billion dollars in damages.

Courtesy of NASA.gov

Hurricane Luis

Since 1953, Atlantic tropical storms have been named from lists originated by the National Hurricane Center. They are now maintained and updated by an international committee of theWorld Meteorological Organization (WMO). Six lists are used in rotation. Thus, the 2006 list will be used again in 2012. If a storm is particularly deadly or costly, it's name is usually retired for reasons of sensitivity. At an annual meeting of the WMO, the name gets stricken from the list and a new name is picked.

The WMO maintains lists of names for not only the Atlantic, but also the Eastern North Pacific, Central North Pacific, Western North Pacific, Western Australian Region, Eastern Australian Region, Northern Australian Region, Fiji Region, Papua New Guinea Region, Philippine Region, Northern Indian Ocean and Southwest Indian Ocean. How many lists are used per region and how they are rotated depends on the region.

MORE INFO: www.nhc.noaa.gov

To send a weather question to our Met Mailbag, click on this link, and check back next week to see if your question is answered!

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Met Mailbag (NBC Weather Plus Meteorologists)

May 25, 2006 | 7:00 p.m. ET

Question: What is the dewpoint, and why is it important to weather?
Submitted by Will McGrew, Chicago, IL

Answer: Thanks for the question, Will.

The dewpoint is a measure of moisture in the air. It's simply the temperature to which air must be cooled in order to reach saturation. So if the air temperature is 60 degrees and the dewpoint is 55, the air will become saturated if the air cools to 55 degrees. At this point, when the air temperature and dewpoint temperature are equal, the relative humidity is 100% and the saturated air can't hold any more water vapor. Any further cooling will result in condensation where cloud development and precipitation is possible.

The higher the dewpoint, the higher the moisture content of the air. Once the dewpoint temperature reaches about 70 degrees, the air becomes uncomfortably humid. The dewpoint gives you a much better idea of how humid it will feel outside on a summer day as compared to the relative humidity. Think about it this way...on a cool day, the air temperature and dewpoint may both be 40 degrees, resulting in 100% relative humidity, but it doesn't really feel humid, does it? That's because cooler air can't hold as much moisture. On the flip side, on a hot summer day when the air temperature is 85 degrees and the dewpoint is 70, the relative humidity is only 54%. If you want to know if it's going to be a sticky day, check the dewpoint!

Click here to watch Kristen's on-air answer.

To send a weather question to our Met Mailbag, click on this link, and check back next week to see if your question is answered!

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Met Mailbag (NBC Weather Plus Meteorologists)

May 18, 2006 | 9:55 a.m. ET

Question: How is the UV Index calculated?
Submitted by Lenny Johns, Denton, TX

Answer: Thanks for the question Lenny. To answer your question we must first explain exactly what the UV Index is. The Ultraviolet Index is a tool the government uses to alert the public about the level of harmful UV rays on a daily basis. Developed by the National Weather Service and the Environmental Protection Agency, the UV Index provides a daily forecast of the amount of ultraviolet radiation expected to reach the Earth’s surface. In turn, it lets people know their risk of overexposure to the sun’s harmful rays.

So how is the UV Index calculated? According to the EPA, calculation of the UV Index starts with a pair of satellites that measure current, total, and worldwide ozone amounts. Remember that ozone is an odorless, colorless gas in the stratosphere that helps reduce the amount of radiation that reaches the Earth’s surface.

RELATED: The UV Index

The data from the satellites is then used to produce a forecast of ozone levels for the next day at various points around the country. A model is then used to determine the amount of UV radiation that will reach the ground using the time of day, day of the year, and latitude.

This information is then weighted according to how human skin responds to each wavelength. Obviously it is more important to protect people from wavelengths that harm skin than from wavelengths that do not.

RELATED: Skin Safety

At each wavelength, the actual incoming radiation level is multiplied by the weighting. These weighted irradiances are totaled, or integrated, over the spectrum of UV wavelengths resulting in a value representing the total effect a given day's UV radiation will have on skin.

These estimates are then adjusted for the effects of elevation and clouds, then divided by a conversion factor of 25 and rounded to the nearest whole number.

This results in a number that usually ranges from 0 (where there is no sunlight) to the mid teens. This value is the UV Index.

UV Index Number Exposure Level:

0 to 2

3 to 5

6 to 8

8 to 10

11+

Pretty complicated! Just remember, the higher the UV Index number, the higher the exposure to harmful UV rays.

To send a question or comment to our NBC Weather Plus team, click here

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Met Mailbag (NBC Weather Plus Meteorologists)

May 10, 2006 | 12:00 p.m. ET

Met Mailbag is your chance to have a Weather Plus Meteorologist answer your weather question. Each Thursday, our NBC Weather Pulse Blog will publish the answers to questions you send us. This week's questions were answered by NBC Weather Plus Meteorologist Bill Karins.

Question: While everyone is gearing up for the Atlantic hurricane season on June 1, we can't forget that starting on May 15 is the beginning of the Pacific hurricane season. The last 3 years it has been non-active on that side I think due to La Nina or the El Nino pattern off the Baja peninsula or in the Pacific Ocean.

So my question is: Do you think the pattern will be the same this year or will there also be an active period as in the Atlantic region?
Submitted by Michael Williams

Answer: Hi Michael, you are right, 99% of the hurricane coverage in the media is spent on the Atlantic side. If you look at just the number of storms each year you have to ask why? The Atlantic Ocean averages 10 named storms a year while the Pacific Ocean averages 17 named storms and in an average year, nine of these would become hurricanes, of which five would become major hurricanes. The reason for the huge media bias is because the storms that form in the Pacific usually move away from North America safely out to sea while the storms that form in the Atlantic move towards land areas. A few of the Pacific storms do curl back towards Mexico and Central America every now and then and a few popular resort cities have seen storm damage including Acapulco, Cabo San Lucus and Puntarenas. What about California? Hurricanes feed off of warm water and to put it simply the water off of California is just too cold for tropical systems to thrive and hit California.

The East Pacific hurricane season runs from May 15th through November 30 with the peak July through September. The national hurricane center will release their prediction for the number of storms in the Pacific Ocean on May 15th. Here is a great chart from the National Hurricane Center showing the average dates of Pacific named storms.

In my opinion, the answer to your question is yes, I do expect a similar weather pattern in the Pacific Ocean this year to last year. As a result, I expect a slightly below average storm season. I will let the experts at the hurricane center give you specific numbers but the average is 17 and in 2005 we saw 15. I’d be surprised if their prediction wasn’t somewhere close to this. In 2004 we saw 12 named storms and in 2003 we had 16. There appears to be a seesaw effect with the Pacific and Atlantic oceans during active years. When the Atlantic is active like the past few years the Pacific has been calmer and back in the ‘90s it was the other way around. In general, when we are in a La Nina pattern (like now) the Atlantic is active and the Pacific is quieter. In an El Nino year, it is just the opposite. Hopes this helps and thanks for the question.

To send a question or comment to our NBC Weather Plus team, click here

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Met Mailbag (NBC Weather Plus Meteorologists)

May 3, 2006 | 1:00 p.m. ET

Met Mailbag is your chance to have a Weather Plus Meteorologist answer your weather question. Each Thursday, our NBC Weather Pulse Blog will publish the answers to questions you send us. This week's questions were answered by NBC Weather Plus Meteorologist Jeff Ranieri.

Question: What makes wind?
Submitted by Joshua Chanin, New York City

Answer: Well Josh, wind is something that can be either annoying or enjoyable at times and the way it develops is a bit complex but interesting. Read on and you'll see how to do your own wind experiment.

Wind is Mother Nature’s way of balancing out the atmosphere. Wind is created largely by pressure differences. So, let’s start off by explaining pressure in weather terms. High pressure is generally an area of clearing where the air is sinking and the atmosphere is heavier or has more mass. Low pressure creates rising air leaving the surface where we live with less weight or air mass and can lead to cloud or storm development.

Now that we have an idea about pressure, it's somewhat simple to understand. High pressure, the area with more weight, will rush into low pressure, in an attempt to equal out the air space and make the air around us the same weight. When this equalization is happening it can create anything from strong gusts to a light breeze. The bigger the difference between "high" and "low" pressure the stronger the wind will be.

You can make or see the effects of how we get wind somewhat easy. If you go to the store and grab acoffee can that is vacuum packed it will demonstrate wind. Before you open the lid think about the can and the air. Outside the can you have higher pressure or mass. Inside the can, a machine has lifted out the air prior to packing to keep it fresh. Therefore, the weight of the air in the can is lighter. When you open the coffee the higher pressure outside will rush into the can to equal the space in the can. You will hear a sound when it's opened and that rushing noise will be a small example of wind!

One way to spot windy or breezy areas is by looking at a temperature map. Huge differences in temperature will create wind. If you remember back, we talked about high and low pressure. Where you have high pressure it tends to be warmer and where you have low pressure it can signify cooling on the way. These clashing warm and cool areas will work to balance themselves out and create wind in the process.

To send a question or comment to our NBC Weather Plus team, click here

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Met Mailbag (NBC Weather Plus Meteorologists)

April 26, 2006 | 1:40 p.m. ET

Met Mailbag is your chance to have a Weather Plus Meteorologist answer your weather question. Each Thursday, our NBC Weather Pulse Blog will publish the answers to questions you send us. This week's questions were answered by NBC Weather Plus Meteorologist Jackie Meretsky.

Question: What does it mean when the lighting strikes sideways?
Submitted by Frederick Langley

Answer: Lightning, very similar to a spark, is the release of electrical energy in the sky. As it is released, it provides a conductive path along which a current can run and neutralize the charge.

Generally, this charge occurs between the cloud and the ground, however, there are times when the discharge begins at the side of a cloud and move sideways into the clear air. Instead of helping to neutralize the cloud charge, the charge is transported away from a highly charged region to a place of lower charge, from one thunderstorm cell to another. It almost looks as if the clouds are bowling…and if this were in fact the case, the most popular bowlerama would be perched over tornado alley. This is sometimes called a cloud-to-cloud flash and is particularly dangerous! A cloud-to-cloud flash of lightning can travel sideways for up to 25 miles before it strikes the ground, thus increasing the unpredictability of the strike.

Question: What causes the changes in the direction of the jet stream?
Submitted by Dorian Johnson, Kennedale, Texas

Answer: The jet stream, one of the most powerful elements of nature, is a fast flowing current of air formed by temperature differences in the upper atmosphere. Temperature changes, in turn, cause pressure differences, which forces the air to move. Generally, because of the rotation of the earth, the winds along the jet stream blow from west to east. However, the jet stream winds are greatly affected by changes in temperature, which can cause a change in the direction of flow. When this occurs, you will hear meteorologists often talk about ridges and troughs causing amplifications (a wavy pattern) in the jet stream flow. Wind shear (a sudden change in wind direction and speed) can also alter the direction of the jet stream.

To send a weather question to our Met Mailbag, click on this link, and check back next week to see if your question is answered!

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