National Weather Service United States Department of Commerce
Severe Weather Preparedness Week in Southern New England: April 28 - May 2, 2014

For more information, please visit the National Severe Weather Preparedness Page

The National Weather Service in Taunton will feature a different Severe Weather related topic each day during the Awareness Week.
DEFINITION OF A SEVERE THUNDERSTORM

A 'Severe Thunderstorm' is defined as a thunderstorm that produces wind gusts of at least 58 mph and/or hail 1.00 inches in diameter or larger...the size of a quarter. Severe thunderstorms can and occasionally do spawn tornadoes.

A Severe Thunderstorm Watch is issued by the Storm Prediction Center in Norman, Oklahoma for large portions of the region when the potential exists for severe thunderstorms. A Severe Thunderstorm Warning is issued by the local National Weather Service Forecast Office, such as in Taunton, when severe thunderstorms are imminent based on radar or already occurring based on spotter observations.

Note that torrential downpours of rain that cause flooding are not part of the definition of 'severe.' They would prompt the issuance of Flood or Flash Flood Warnings, but not Severe Thunderstorm Warnings. It is important to note that frequent lightning also is NOT a criteria for what is termed 'severe.' Of course lightning can be extremely dangerous, but every thunderstorm has lightning -- that is what causes the thunder. It is not practical to issue a warning for every thunderstorm, thus we issue Severe Thunderstorm Warnings for those storms that could produce large hail and damaging winds.

NOAA Weather Radios, with warning alarm tones, will alert you when a Severe Thunderstorm Warning is issued. However, they will not sound an alarm for non-severe thunderstorms, which still can produce deadly lightning. We recommend that lifeguards at beaches and pools have hand-held lightning detectors. The same is true for athletic coaches, camp directors, and parks and recreation workers. Even without equipment, you can protect yourself by moving indoors to a place of safety at the first rumble of thunder. If you can hear the thunder, the storm is usually close enough for you to have the potential to be struck by lightning.

THUNDERSTORMS AND LIGHTNING

Summertime is a good time for outdoor recreational activities in New England. It is also the time of the year when thunderstorms are most likely. Thunderstorms can be beautiful, but they also can be deadly. While many people think they are aware of the dangers of thunderstorms and lightning, the vast majority are not.

There are three basic ingredients needed for the formation of a thunderstorm. They include low-level moisture, an unstable atmosphere, and a trigger (a source of lift).

Low-level moisture:
This moisture is needed for cloud formation, growth, and the development of precipitation within the cloud.


Unstable atmosphere:
An unstable atmosphere allows warm, moist air near the ground to rise rapidly to higher levels in the atmosphere where temperatures are below freezing. An unstable atmosphere also allows air at higher levels in the atmosphere to sink to the ground level rapidly, bringing stronger winds from the higher levels to the ground.

A trigger:
Something to set the atmosphere in motion.

All three ingredients contribute to the formation of a thunderstorm. In fact, as the magnitudes of these ingredients increase, so do the chances that a Thunderstorm could become severe.

In the summertime, listen to the latest forecast and learn to recognize the signs which often precede thunderstorm development. Warm muggy air is a sign that ample low-level moisture is available for thunderstorm development. Towering cumulus clouds indicate an atmosphere that is, or is becoming, unstable. And, the trigger could be continued heating from the sun; an approaching front or sea breeze front; or a cooling of the upper atmosphere.

All thunderstorms go through various stages of growth and development. As a thunderstorm cloud continues to grow, snow and ice begin to form in the higher levels of the cloud where temperatures are below freezing and electrical charges start to build up within the cloud. Negative electrical charges near the middle and base of the cloud cause a positive charge to build up on the ground under and near the thunderstorm. Finally, when the difference between these charges becomes to great, a giant atmospheric spark that we call lightning occurs.

Lightning is an underrated killer, usually claiming its victims one at a time. Lightning also leaves many victims with life-long serious injuries. Lightning can strike as far as 10 miles from the side of the thunderstorm cloud. In fact, many lightning victims are struck before the rain arrives or after the rain has ended and the storm is moving away. Most victims also report that at least a portion of the sky was blue when they were struck.

While inside a home or building

  1. Avoid any contact with corded phones.
  2. Avoid any contact with electrical or electronic equipment or cords that are plugged into the electrical system.
  3. Avoid any contact with the plumbing system. Do not wash your hands, do not wash the dishes, do not take a shower, or do not do laundry.
  4. Do not stand next to a concrete wall and do not lie on a concrete floor.
  5. Stay away from windows, outside doorways, and porches.
Tips while outdoors
  1. Plan outside activities so that you minimize the risk of being caught outside in a thunderstorm.
  2. If you hear thunder, move inside a safe shelter immediately. Generally, if you can hear the thunder, you're within striking distance of the storm.
  3. If the sky looks threatening, move inside immediately. Don't wait for the first stroke of lightning. It could occur anywhere under or near the storm.
  4. Stay inside a safe shelter for at least 30 minutes after the last rumble of thunder was heard. Many lightning victims are struck after the worst part of the storm has passed.
  5. If you are caught outside in a thunderstorm and can't reach a safe shelter, you can only minimize your risk of being struck by lightning. If lightning strikes near you, it will most likely strike the tallest object in your immediate vicinity. First, don't be the tallest object in the immediate vicinity and don't be near the tallest object. Second, get as low as possible to the ground, but minimize your contact with the ground. Do not lie on the ground.

Remember, when it comes to thunderstorm safety, it's your own actions that will determine your personal risk of being killed or seriously injured by the hazards of a thunderstorm.

WIRELESS EMERGENCY ALERTS AND A SUCCESS STORY IN CONNECTICUT

Beginning in June 2012 the Wireless Association and the Wireless Industry joined the Federal Communications Commission /FCC/ and the Federal Emergency Management Agency /FEMA/ to offer Americans a robust and reliable wireless Emergency Alert System. Wireless Emergency Alerts /WEA/ include Amber Alerts and many of you may have already noticed that your new smart phone alerted for a Flash Flood Warning or Tornado Warning in your area.

If you are driving into an area that is in a Tornado Warning, your new smart phone will automatically alert. There are no fees for this service. If you acknowledge the alert once then you will not continue to receive it for the same warning event. If purchasing a new phone, be sure to ask if it is WEA enabled.



Severe Thunderstorm Warnings are not automatically sent at this time as a WEA Alert. The reason for this is that although severe thunderstorms can cause huge hail or life-threatening downbursts, warnings are also issued for lower-end events with only one-inch diameter hail or wind gusts to 58 mph. There are too many of these events nationwide to warrant triggering the wea alert, it would not be good if people became immune to these alerts and disregarded them.

On July 1 2013, a tornado touched down in East Windsor, Connecticut shortly after 130 pm in the afternoon. The manager of an inflatable soccer dome sports complex, and another counselor, both noticed that their cell phones were alerting that a Tornado Warning had been issued for their area from the National Weather Service. The manager and five counselors then rushed 29 children into an adjoining building where they took cover. Within a few minutes the tornado hit the complex, ripped off the dome, and threw it high above Interstate 91. Thanks to the quick action by the staff in response to this new means of alerting there were no injuries. Quite a success story!

TORNADO SAFETY IN SCHOOLS

Every school should have a Tornado Safety Plan. The plan should ensure that everyone will take cover within 60 seconds. Frequent tornado drills should be conducted. There should be provisions for all after-hours school-related activities.

Every school should be inspected and tornado shelter areas designated by a registered engineer or architect. Rooms with exterior walls should never be used as tornado shelters. Basements offer the best protection. Schools without basements should use interior rooms and hallways on the lowest floor away from windows.

Schools should delay assemblies or lunch in large rooms with wide roof spans, such as gymnasiums, auditoriums, and cafeterias. These rooms offer little or no protection for tornado-strength winds and the wide-spanned roofs can collapse.



Students and staff should know the protective position, sitting and facing an interior wall, elbows to knees, and with hands over the back of their heads.

Each school should have a NOAA Weather Radio with battery backup. Remember that the National Weather Service issues a Tornado Watch when conditions are favorable for tornado development and a Tornado Warning when a tornado has been spotted or indicated by radar.

If the alarm system of a school relies on electricity, there should be an alternative method to notify teachers and students in case of power failure.

Please remember to make special provisions for faculty and students with disabilities, those with portable classrooms, and those outdoors. Keep children at school beyond regular hours during a Tornado Warning. For that matter, it would be good practice to delay departure of school buses with Severe Thunderstorm Warnings, too, since they can produce large hail and damaging winds without a tornado.

When planning additions or new school buildings, be sure to include properly designed tornado shelters.

DOWNBURST WINDS FROM SEVERE THUNDERSTORMS CAN BE POWERFUL

While not as notorious or perhaps as spectacular to witness as a tornado, straight-line winds are responsible for most thunderstorm wind damage, especially across southern New England.

A downburst is a strong and relatively small area of rapidly descending air beneath a thunderstorm. It can result from stronger jet stream winds being transported downward to the surface, or it can result as air within the downburst is cooled significantly as rain evaporates into initially drier air. This cool, thus dense, air sinks rapidly to the surface. A downburst is differentiated from a common thunderstorm downdraft because the winds it produces have the potential to cause damage on or near the ground. Surface damage patterns have shown that whether the winds are straight or a little bit curved, they tend to spread out, or diverge, considerably as they reach the surface. Conversely, damage patterns resulting from a Tornado generally converge toward a narrow central track.


Intense downbursts can be phenomenal. Speeds have been clocked as high as 175 mph near Morehead City, North Carolina and at 158 mph at Andrews Air Force Base in Maryland. Closer to home, 104 mph downburst winds were measured at both Worcester, Massachusetts on May 31, 1998 and Whitman, Massachusetts on May 21, 1996. Strong downbursts will definitely cause roaring sounds and people may often refer to a sound like a freight train, terms typically associated with tornadoes. Although downbursts are not tornadoes, they can cause damage equivalent to that of a small to medium tornado. After all, wind is wind.

Downbursts are classified as either macrobursts or microbursts, depending on the areal extent of the damaging wind swath. A macroburst's damage extends horizontally for more than 2.5 miles. A microburst is a small downburst with its damaging winds extending 2.5 miles or less. The small horizontal scale and short time span of a microburst makes it particularly hazardous to aviation.

The National Weather Service issues Severe Thunderstorm Warnings for thunderstorms that are expected to produce damaging wind gusts of 58 mph or greater, or hail that is one inch or greater in diameter.