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.

EF-0: light damage (winds 65 to 85 mph)
EF-1: moderate damage (winds 86 to 110 mph)
EF-2: considerable damage (winds 111 to 135 mph)
EF-3: severe damage (winds 136 to 165 mph)
EF-4: devastating damage (winds 166 to 200 mph)
EF-5: incredible damage (winds over 200 mph)

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.

Recent tornadoes

Here is a list of the tornadoes reported in Maine and New Hampshire since 1995:

EF2/F2

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)

EF1/F1

July 23 1995 New Hampton, New Hampshire
June 21 1997 Rome, Maine
July 03 1997 Swanzey, New Hampshire
October 01 1998 South Paris, Maine
August 13 1999 Sweden, Maine
August 13 1999 Plainfield/Enfield, New Hampshire
July 18 2000 Newry/Hanover, Maine
June 17 2001 Newry/Hanover, Maine
July 24 2001 Penobscot county (16 miles northwest of Patten)
July 24 2001 Oakfield, Maine
May 31 2002 West Paris, Maine
July 04 2002 Aroostook county (8 miles west of Littleton)
November 24 2005 Phippsburg, Maine
September 29 2006 North Berwick, Maine
May 24 2009 Eagle Lake, Maine
May 31 2009 Westfield, Maine
May 31 2009 Easton, Maine
August 21 2009 Norway to Hartford, Maine (up to 700 yards wide)
June 5 2010 South Paris, Oxford, Hebron, Maine
July 21 2010 Newfield to Limerick, Maine
July 21 2010 Buxton to Gorham, Maine
July 21 2010 Shapleigh to Alfred, Maine
June 1 2011 Bryant Pond, Maine
June 1 2011 New Portland to Embden, Maine
August 21 2011 Canaan, New Hampshire

EF0/F0

July 28 1997 Fort Kent, Maine
August 27 1997 Charleston, Maine
July 23 2002 Aroostook County (7 miles northwest of Knowles corner)
August 08 2004 Sebago Lake, Maine
August 13 2004 Sanbornton/Meredith, New Hampshire
August 01 2005 North Twin Lake, Maine
November 24 2005 Brunswick, Maine
September 29 2006 Effingham, New Hampshire
July 15 2007 Long Lake in Aroostook county, Maine
May 31 2009 Oxbow, Maine
June 26 2009 Stockholm, Maine
July 18 2009 East Bethel, Maine
June 2 2010 Shin Pond, Maine
June 5 2010 Gorham, New Hampshire
June 8 2011 Little Madawaska lake, Maine
June 8 2011 Aroostook County, Maine
June 9 2011 Aroostook County, Maine
July 26 2011 Colebrook, New Hampshire

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:

Flying debris causes most deaths and injuries in tornadoes
The safest place in your home during a tornado is your basement.
Stay away from windows.
Get out of vehicles or mobile homes, they offer little protection. Seek shelter in a substantial building.
Do not seek shelter under a bridge overpass. Bridge overpasses offer little, if any, protection from wind- driven debris.

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:

National Weather Service Gray: covers western and Southern Maine, include York, Cumberland, Sagadahoc, Lincoln, Knox, Waldo, Androscoggin, Oxford, Franklin and Kennebec Counties, and central and southern Somerset County.
National Weather Service Caribou: covers eastern and Northern Maine, including Aroostook, Penobscot, Washington, Hancock, Piscataquis and northern Somerset County.

MAINE EMERGENCY MANAGEMENT AGENCY