The National Weather Service is observing Severe Weather Awareness Week this week (2-6 May) in New England and New York.
The National Weather Service advises that it is important to understand hazardous weather terminology in order to take proper action if and when severe weather threatens.
When a severe thunderstorm watch is issued, it covers a large area (possibly several counties or a state), and it is valid for a lengthy period of time (e.g., 4-8 hours). It is issued when conditions are favorable for the possible development of severe weather in the area. A severe thunderstorm includes damaging winds (steady or gusts) in excess of 58 miles per hour, hail with a diameter of one inch or larger (i.e., the size of a quarter), and, possibly, a tornado. A severe thunderstorm watch is issued by the NWS Storm Prediction Center in Norman, Oklahoma.
A severe thunderstorm warning is issued by county for a relatively short period of time (an hour or less) when severe weather is imminent (based on radar) or is observed (based on spotter observations). A severe thunderstorm warning is issued by the local NWS forecast office.
Although severe thunderstorms may contain deadly lightning and heavy rain capable of producing floods, they are not part of the definition of severe. Torrential downpours of rain that cause flooding would prompt the issuance of flood or flash flood warnings. Every thunderstorm has lightning (that is what causes the thunder), but it is not practical to issue a warning for every thunderstorm. Consequently, NWS issues severe thunderstorm warnings for those storms that could produce large hail and damaging winds
Other Severe Weather
A tornado watch covers a large area (possibly several counties or a state), and it is valid for a lengthy period of time (e.g., 4-8 hours). It is issued when conditions are favorable for the possible development of severe weather, including tornadoes.
A tornado warning is issued by county for a relatively short period of time (an hour or less) when severe weather has been detected by Doppler radar or has been observed.
A flood watch covers a large area (possibly several counties or a state), and it is valid for a lengthy period of time (e.g., greater than six hours). It is issued when the threat of heavy rainfall during the course of the watch period increases the potential for flooding that may endanger life and property. In mountainous terrain, heavy rain in a short period of time may lead to devastating flash flooding.
A flood or flash flood warning is issued when observed rainfall, compared with local flood guidance, indicates that flooding is imminent or when flooding is actually observed.
The National Weather Service advises that, despite great advances in weather detecting technology, a network of trained personnel, and a number of severe weather products, people die from weather-related causes each year because they did not know about the warning.
NWS advises that a battery-operated NOAA all-hazards weather radio with tone alert capabilities is one of the quickest and most reliable ways to receive severe weather information.
For more information, please visit:
National Weather Service National Headquarters: Definition of a Severe Thunderstorm
SPC: Severe Thunderstorm Event: July 21, 2010
For forecasts and other severe weather information, please visit (these are the weather forecast offices that cover New England):
National Weather Service: Weather Forecast Office, Caribou, ME
National Weather Service: Weather Forecast Office, Gray/Portland, ME
National Weather Service: Weather Forecast Office, Taunton/Boston, MA
National Weather Service: Weather Forecast Office, Burlington, VT
National Weather Service: Weather Forecast Office, Albany, NY
National Weather Service: Weather Forecast Office, Upton/New York City, NY
National Weather Service Storm Prediction Center
Severe Weather Awareness Week PSAs
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