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Home > Severe Weather Awareness: Focus on Tornadoes
Severe Weather Awareness: Focus on Tornadoes
May 3, 2012
Tornadoes are nature's most violent storm. By definition, a tornado is a violently rotating column of air that extends from the base of the thunderstorm cloud to the ground.
In addition to the three basic ingredients needed for the formation of thunderstorms and severe thunderstorms (low-level moisture, an unstable atmosphere, and a source of lift), winds at various levels in the atmosphere factor into the development of tornadoes.
Usually, prior to the development of a tornado, a pre-tornadic thunderstorm develops a circulation, that is, it starts rotating (becomes a meso-cyclone). As this rotation becomes stronger, the chance that a tornado may develop also increases.
Although the National Weather Service's Doppler radar generally can not see the actual tornado, the radar does detect rotation of the thunderstorm cloud. It thereby gives some indication of the possibility that a tornado may be forming or has formed.
The scale used to measure tornado damage is the Enhanced Fujita Scale (named after Theodore Fujita, a famous tornado damage expert). This scale is commonly referred to as the E-F Scale. Based on scientific studies of tornado damage, the original Fujita Scale was modified and the new "Enhanced Fujita Scale" was officially implemented in 2007.
Peak tornado activity in northern New England occurs between June and August, but tornadoes have occurred as early as May and as late as November. Most tornadoes occur between 3 and 9 pm and have an average forward speed of about 30 mph.
For the 40 year period between 1950 and 1990, 74 tornadoes occurred in Maine while 68 tornadoes occurred in New Hampshire. Based on these data, each state had averaged about two tornadoes per year. During this period, the average path length of the tornadoes was 1.08 miles for Maine and 1.64 miles for New Hampshire. The strongest tornado observed in Maine was an F2, while the strongest tornado observed in New Hampshire was an F3.
During 2011, there were five tornadoes recorded in Maine and two tornadoes in New Hampshire. June 1 and June 8 were the most active days during 2011, each with 2 tornadoes.
Here is a list of the tornadoes reported in Maine and New Hampshire since 1995:
July 08 1996 Cobbosseecontee Lake, Maine July 03 1997 Greenfield, New Hampshire May 31 1998 Antrim, New Hampshire July 06 1999 Pittsfield/Barnstead/Strafford, New Hampshire August 09 2000 Cornville, Maine May 21 2006 Hampton Falls, New Hampshire July 24 2008 Deerfield to Freedom, New Hampshire (50 mile path length)
Pay attention and be safe ...
To alert the public to the threat of tornadoes, the National Weather Service issues Tornado Watches and Warnings. A Tornado Watch indicates that atmospheric conditions are favorable for the development of tornadoes.
A Tornado Warning indicates that a tornado is imminent or is already occurring. If you hear that a Tornado Warning has been issued for your area, seek safe shelter immediately if you are in the path of the storm.
Due to the usual short life-span of tornadoes in northern New England, there is often little, if any, advance warning. Tornadoes in New England generally touch down and then lift off the ground very quickly. Many of the tornadoes that have occurred in the past have occurred while Severe Thunderstorm Warnings have been in effect.
If you hear that a Severe Thunderstorm Warning is in effect for your area, be alert for the possibility of a tornado. A low rotating cloud, large hail, and/or a load roar are all signs that may precede the touchdown of a tornado.
Here are some tornado facts and safety tips:
Severe Weather Awareness Week ...
The National Weather Service has declared the week of April 30th through May 4th Severe Weather Awareness Week in New England. Today's message is presented in partnership with the National Weather Service Forecast Offices in Maine:
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