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Thunderstorms Questions Answered

Have you ever heard of thundersnow?

Contrary to popular belief, thunder and lightning are not just reserved for the warm season.  In some cases, thunderstorms can form where snow falls.  This is called thundersnow, and although rare, it does occur. 

These storms are not common due to the fact that thunderstorms need plenty of moisture and instability (vertical motion), which the cold winter air usually does not often contain. Arctic air masses are not capable of holding much water, and their dense qualities make high levels of instability hard to achieve.

However, in lake effect snow after a strong winter cold front passes, mild air over the lake can be lifted fast enough for the development of thunderstorm activity.  This often occurs in late Autumn when arctic air begins to flood the region, and the lake waters are still relatively warm.


Lightning Safety

The commotion of a thunderstorm is attention grabbing, but be aware if you happen to be near one. According to the National Weather Service (NWS) 67 people are killed by lightning strikes every year, with many more lightning related injuries occurring.

Here are some tips when caught in severe thunderstorms:

If possible, avoid water, open spaces and all metal objects including electric wires or fences. Unsafe places include canopies, small picnic shelters, and tall trees.

When possible, find shelter in a substantial building or in a fully enclosed metal vehicle. If you are caught outside and lightning is striking nearby, do not gather in close proximity to other people.

On average Western New York has nearly 40 thunderstorms every year. For more lightning safety information, go to http://www.lightningsafety.noaa.gov/.


What is thunder?

I know my mother used to tell me it was the angels bowling, but we know its the result of lightning.

A bolt of lightning is extremely hot. The air within this channel has been estimated at over 50,000 degrees Fahrenheit. This heating takes place very rapidly causing air molecules to expand. The result is a series of compressions in the atmosphere that are produced because of the elasticity of the surrounding air. It is this audible shock wave that we call thunder.

Lightning is seen first and then the thunder follows afterwards because light travels faster than sound. But if you happen to be in the unpleasant position of being near a lightning strike, both the lightning and thunder will seem to happen simultaneously. A typical clap of thunder will register approximately 120 Dba (decibels), almost as loud as a jet engine.


What is the criteria for a "severe" thunderstorm?

Many of us have experienced the awe of thunderstorms, but there are specific factors that qualify a thunderstorm as severe. 

The National Weather Service in Buffalo is responsible for issuing watches and warnings for our area. A severe thunderstorm is defined as a thunderstorm capable of producing a tornado, containing wind gusts of at least 58 miles per hour, or hail of an inch or larger.

When a thunderstorm with any of these criteria is detected, a warning is issued. Without meeting these specific standards, even the most potent thunderstorm wont be issued a warning.

The weather staff at 13WHAM-TV is staffed by at least one meteorologist almost around the clock. This enables us to inform our viewers of any potentially life threatening weather.


What’s the significance of straight-line winds in a thunderstorm?

Straight-line winds are often responsible for most of the wind damage associated with a severe thunderstorm. These high speed winds are common with the gust front of a thunderstorm or they originate with a down burst from a thunderstorm.

These winds are often confused with tornadoes because of the amount of damage that can be produced. The National Weather Service will usually survey the damage after the event and look for signs of a tornado. If there is a lack of a rotation in the damage pattern it is classified as straight-line winds.

One of the most destructive examples of this was Wichita, Kan., on June 19, 1990. Winds were clocked at 116 mph and produced more then $50 million dollars in damage. Winds toppled trees, ripped apart small buildings, and knocked down more than 1,000 power poles.


What signs should boaters look for in anticipation of a thunderstorm?

On a sunny day, look for Cumulus clouds. These are the puffy clouds that look like balls of cotton in the atmosphere. These clouds will start to build vertically if the atmosphere is unstable.

Common sense would dictate listening to a weather report. If the dew point temperature is above 60 degrees this could mean that the potential for heavy drenching thunderstorms is higher.

If a forecast calls for thunderstorms; be observant of the wind direction out on the water. Wind direction will change if thunderstorms are in the area.

When you see black clouds rolling in get off the water if possible! At this point it could be too late and you may have to weather the storm. Remember rain can limit your horizontal visibility.


Who receives the most thunderstorm activity each season in the U.S.?

The answer here is definitely Florida. Areas around Orlando and Tampa are often considered the lightning capitols of the world. Residents in these areas will see over 100 days of thunderstorm activity each season.

A footnote, Rochester on average, will see between 30-40 days of thunderstorm activity each year.


What town in the United States almost never records a thunderstorm?

The answer is Barrow, Alaska. Barrow is located on the extremely cold far North coast of Alaska. According to the National Weather Service on June 20, 2000, Barrow had thunderstorm activity for the first time in several decades.


Have you ever heard of the weather term called "CAPE"?

Anytime there is the threat of thunderstorms in our area meteorologists are discussing the value of the CAPE. CAPE stands for Convective Available Potential Energy and is a measure of the amount of energy available for convection. The higher this number reaches the greater potential for severe weather and strong thunderstorms. This energy value is directly related to the vertical wind speed within the updraft of thunderstorm.

CAPE is one of many indices which are produced by computer models to simulate future weather. However, it is important to note that many other elements are considered before making a forecast for thunderstorms such as availability of moisture or wind shear.


What is the relationship between the height of cloud tops in thunderstorms and the severity of those storms?

One rule is that the higher the cloud-top the greater the severity of the storm, although this is not always the case. What we call the "garden variety" of thunderstorms will usually reach 20,000 to 30,000 feet. These types of storms are afternoon thunderstorms caused by daytime heating, lake, land, and sea breezes. These storms are usually not severe.

In the Midwest though, thunderstorms typically reach much higher into the atmosphere. Radar operators have estimated storm heights from 65,000 to 70,000 feet. These storms will occasionally "punch" though the tropopause (layer between the troposphere and stratosphere) and several thousand feet into the stratosphere. This will cause a cauliflower effect on a satellite image. These types of storms usually produce large hail, damaging winds and occasionally tornadoes.


What ingredients are needed to produce thunderstorms?

There are three basic ingredients needed for thunderstorm development.

One factor is moisture. The moisture in the air is what the clouds, and eventually the rain, will develop from.

The second thing needed is an unstable atmosphere. For the atmosphere to be unstable there has to be relatively warm air located under cooler air. The warm air is less dense, and will rise through the cooler air. This releases heat and energy into the atmosphere.

The third necessary ingredient is a "trigger." A trigger can be a cold front, warm front, trough, upper level disturbance or even a lake breeze boundary.

When all these features are put together, the trigger forces the warmer air to rise through the unstable atmosphere. The rising moist air causes clouds to form and that could lead to a thunderstorm.


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