Tornado watch
A tornado watch (SAME code: TOA, sometimes referred to as a red box by meteorologists and storm chasers) is issued when conditions are right for a tornado to form.[1] Since any thunderstorm capable of producing a tornado is defined as severe, a tornado watch is also automatically a severe thunderstorm watch.[2] In most cases, the potential exists for large hail and/or damaging winds in addition to the tornadoes.
A tornado watch must not be confused with a tornado warning: a watch does not imply that the severe weather is actually occurring, only that conditions have created a significant risk for it. If severe weather actually does occur, a tornado warning or severe thunderstorm warning will be issued.[1]
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[edit] Tornado watches in the United States
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In the United States, the Storm Prediction Center (a national guidance center of the National Weather Service) issues watches for areas likely to produce tornadoes and severe thunderstorms.[1] The watch boxes are usually issued in the format of " __ miles (north and south; east and west; either side) of a line from __ miles (direction) of (City, State), to __ miles (another direction) of (another City, State)." For example: "50 miles either side of a line from 10 miles northeast of Columbia, South Carolina to 15 miles south-southwest of Montgomery, Alabama". (Either side means perpendicular to the center line.)[3] When displayed on a map, they appear as a red outline. In addition, a list of all counties included in its area of responsibility is issued by each NWS forecast office for each watch.[1]
[edit] Examples of United States tornado watches
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URGENT - IMMEDIATE BROADCAST REQUESTED
TORNADO WATCH NUMBER 227
NWS STORM PREDICTION CENTER NORMAN OK
615 PM CDT FRI MAY 4 2007
THE NWS STORM PREDICTION CENTER HAS ISSUED A
TORNADO WATCH FOR PORTIONS OF
WESTERN AND CENTRAL KANSAS
WESTERN AND NORTHERN OKLAHOMA
THE EASTERN TEXAS PANHANDLE AND NORTHWEST TEXAS
EFFECTIVE THIS FRIDAY NIGHT AND SATURDAY MORNING FROM 615 PM
UNTIL 200 AM CDT.
TORNADOES...HAIL TO 3 INCHES IN DIAMETER...THUNDERSTORM WIND
GUSTS TO 70 MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE
AREAS.
THE TORNADO WATCH AREA IS APPROXIMATELY ALONG AND 80 STATUTE
MILES EAST AND WEST OF A LINE FROM 25 MILES WEST NORTHWEST OF
RUSSELL KANSAS TO 75 MILES SOUTH SOUTHEAST OF CHILDRESS TEXAS.
FOR A COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH
OUTLINE UPDATE (WOUS64 KWNS WOU7).
REMEMBER...A TORNADO WATCH MEANS CONDITIONS ARE FAVORABLE FOR
TORNADOES AND SEVERE THUNDERSTORMS IN AND CLOSE TO THE WATCH
AREA. PERSONS IN THESE AREAS SHOULD BE ON THE LOOKOUT FOR
THREATENING WEATHER CONDITIONS AND LISTEN FOR LATER STATEMENTS
AND POSSIBLE WARNINGS.
OTHER WATCH INFORMATION...CONTINUE...WW 226...
DISCUSSION...WIDELY SCATTERED STORMS/SUPERCELLS POSSIBLE IN VERY
UNSTABLE AIR MASS ALONG SLOWLY RETREATING DRY LINE THIS EVENING.
STRENGTHENING ASCENT/WIND FIELD ASSOCIATED WITH APPROACHING FOUR
CORNERS UPPER TROUGH MAY ENHANCE TORNADO POTENTIAL AFTER DARK AS LLJ
INCREASES TO AROUND 50 KTS.
AVIATION...TORNADOES AND A FEW SEVERE THUNDERSTORMS WITH HAIL
SURFACE AND ALOFT TO 3 INCHES. EXTREME TURBULENCE AND SURFACE
WIND GUSTS TO 60 KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO
550. MEAN STORM MOTION VECTOR 24030.
...CORFIDI
[3]
[edit] PDS watches
In the event that a tornado watch is likely to lead to a major tornado outbreak along with possible destructive winds and hail, enhanced wording with the words This is a particularly dangerous situation (PDS) can be added to the watch; this is occasionally issued.[5]
[edit] Tornado watches in Canada
In Canada, the criteria used are the same and watches are issued by regional offices of the Meteorological Service of Canada of Environment Canada in Vancouver, Edmonton, Toronto, Montreal and Halifax, on a county or regional basis.[6]
[edit] See also
[edit] References
- ^ a b c d National Weather Service. "Tornado Watch". Glossary - NOAA's National Weather Service. http://www.nws.noaa.gov/glossary/index.php?word=Tornado+watch. Retrieved 2010-01-17.
- ^ National Weather Service. "Severe thunderstorm". Glossary - NOAA's National Weather Service. http://www.nws.noaa.gov/glossary/index.php?word=severe+thunderstorm. Retrieved 2010-01-17.
- ^ a b Corfidi, Steve (2007-05-04). "Tornado Watch 227". Storm Prediction Center. http://www.spc.noaa.gov/products/watch/2007/ww0227.html. Retrieved 2010-01-17.
- ^ Corfidi, Steve (2009-04-25). "Tornado Watch 186". Storm Prediction Center. http://www.spc.noaa.gov/products/watch/2009/ww0186.html. Retrieved 2010-01-17.
- ^ NOAA (2004-04-18). "Storm Prediction Center Frequently Asked Questions (FAQ)". http://www.spc.noaa.gov/faq#2.7. Retrieved 2008-05-23.
- ^ Environment Canada (2007-07-10). "Tornado watch". Prairie and Northern Region Weather Watch and Weather Warning Criteria. http://www.pnr-rpn.ec.gc.ca/air/severewthr/warning.en.html. Retrieved 2010-01-19.
[edit] External links
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