Tornado watch
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- See Severe weather terminology for a comprehensive article on related weather terms.
A tornado watch (SAME code: TOA; sometimes referred to as a "red box" by meteorologists and storm chasers) is issued when weather conditions are favorable for the development of severe thunderstorms that are capable of producing tornadoes. A tornado watch therefore implies that it is also a severe thunderstorm watch. A tornado watch must not be confused with a tornado warning.
A watch does not mean 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.
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[edit] Information included in a tornado watch
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. The watch boxes (or weather watches, WWs) are usually issued in the format of x miles north and south, or east and west, or either side of a line from y miles direction of city, state, to z 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.) In addition, a list of all counties included in its area of responsibility is now issued by each NWS forecast office for each watch.
[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 particularly dangerous situation (PDS) can be added to the watch; this is occasionally issued.
[edit] Tornado watches in Canada
In Canada, the criteria used is 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.
[edit] Example
Moosonee
8:40 PM EDT Wednesday 1 August 2007
Tornado watch for
Moosonee continued
There is a potential for the formation of a tornado this evening.
This is an alert to the potential development of tornadoes and severe thunderstorms with large hail and damaging winds.
Monitor weather conditions..Listen for updated statements. If threatening weather approaches..Take immediate safety precautions.
At 8:30 PM satellite and lightning detection network indicate a cluster of severe thunderstorms over and west of Moosonee tracking to the east at 50 km/h. Another cluster of storms is well west of Fort Albany..Also tracking eastward at 50 km/h..And should reach Fort Albany in the next couple of hours. These storms are capable of producing damaging wind gusts near 100 km/h..Very large hail greater than 2 centimetres in diameter..And torrential downpours of 50 millimetres of rain in an hour or less. There is also a risk that a tornado may be produced by one of these storms.
As a cold front associated with a disturbance over northern Manitoba crosses Northern Ontario this evening conditions are favourable for the development of thunderstorms. This active cold front has a history of producing thunderstorms with strong winds..Very heavy downpours and frequent lightning as it tracked over southern Manitoba yesterday night. In addition severe thunderstorms may develop along a warm front associated with this disturbance in the vicinity of Attawapiskat.
As the cold front sweeps through Northern Ontario this evening some of these thunderstorms could approach severe limits with main threats being torrential downpours and damaging winds. There is also a possibility that a tornado could form ahead of the cold front or along the warm front.
[edit] Watch county breakdowns and status messages
Watch County Breakdowns are relayed by the Storm Prediction Center, however it is the local NWS offices that decide what counties (in their warning area) are included or excluded in the watch. This is why you will sometimes see counties inside the watch outline that are not included in the counties listed, and vice versa. A Watch Status Message works in a similar fashion; the SPC says in what areas they think a threat still exists, and the NWS offices decide what counties to take out of the watch (the local offices will almost always follow the SPC recommendation on the status messages).[1]
[edit] Example of a tornado watch
SEL0 URGENT - IMMEDIATE BROADCAST REQUESTED TORNADO WATCH NUMBER 600 NWS STORM PREDICTION CENTER NORMAN OK 1030 PM EDT WED AUG 15 2007 THE NWS STORM PREDICTION CENTER HAS ISSUED A TORNADO WATCH FOR PORTIONS OF NORTHERN INDIANA NORTHWEST OHIO LAKE MICHIGAN EFFECTIVE THIS WEDNESDAY NIGHT AND THURSDAY MORNING FROM 1030 PM UNTIL 400 AM EDT. TORNADOES...HAIL TO 1 INCH IN DIAMETER...THUNDERSTORM WIND GUSTS TO 70 MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS. THE TORNADO WATCH AREA IS APPROXIMATELY ALONG AND 40 STATUTE MILES NORTH AND SOUTH OF A LINE FROM 20 MILES SOUTH SOUTHWEST OF VALPARAISO INDIANA TO 65 MILES EAST OF FORT WAYNE INDIANA. FOR A COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU0). 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. DISCUSSION...SMALL MCS OVER NW IND HAS FORMED IN THE PAST 90 MINUTES ON WRN SIDE OF COLD POOL/MCV ASSOCIATED WITH EARLIER CONVECTIVE SYSTEM. THE MCS SHOULD REMAIN STRONG THROUGH EARLY THURSDAY AND TRACK ESE INTO OH. A SUPERCELL NOW PRESENT ON WRN SIDE OF SYSTEM WILL POSE A THREAT FOR ISOLATED TORNADOES...IN ADDITION TO DAMAGING WET MICROBURSTS/ MARGINALLY SVR HAIL...GIVEN HI PWS AND LOW LEVEL WIND FIELD WITH CONSIDERABLE DEGREE OF SPEED/DIRECTIONAL SHEAR. WIND PROFILES MAY ALSO SUPPORT BACK-BUILDING DEVELOPMENT ON WRN SIDE OF MCS...WITH ASSOCIATED LOCALLY HEAVY RAIN POSSIBLE INTO FAR NE IL/NRN IND IN WAKE OF SUPERCELL. AVIATION...TORNADOES AND A FEW SEVERE THUNDERSTORMS WITH HAIL SURFACE AND ALOFT TO 1 INCH. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60 KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 550. MEAN STORM MOTION VECTOR 30030. ...CORFIDI
[edit] Example of a watch county breakdown
WOUS64 KWNS 160227 WOU0 BULLETIN - IMMEDIATE BROADCAST REQUESTED TORNADO WATCH OUTLINE UPDATE FOR WT 600 NWS STORM PREDICTION CENTER NORMAN OK 1030 PM EDT WED AUG 15 2007 TORNADO WATCH 600 IS IN EFFECT UNTIL 400 AM EDT FOR THE FOLLOWING LOCATIONS INC001-003-009-017-033-039-049-053-069-075-085-087-091-099-103- 113-131-141-149-151-169-179-181-183-160800- /O.NEW.KWNS.TO.A.0600.070816T0230Z-070816T0800Z/ IN . INDIANA COUNTIES INCLUDED ARE ADAMS ALLEN BLACKFORD CASS DE KALB ELKHART FULTON GRANT HUNTINGTON JAY KOSCIUSKO LAGRANGE LA PORTE MARSHALL MIAMI NOBLE PULASKI ST. JOSEPH STARKE STEUBEN WABASH WELLS WHITE WHITLEY OHC003-039-051-069-125-137-161-171-160800- /O.NEW.KWNS.TO.A.0600.070816T0230Z-070816T0800Z/ OH . OHIO COUNTIES INCLUDED ARE ALLEN DEFIANCE FULTON HENRY PAULDING PUTNAM VAN WERT WILLIAMS LMZ046-160800- /O.NEW.KWNS.TO.A.0600.070816T0230Z-070816T0800Z/ CW . ADJACENT COASTAL WATERS INCLUDED ARE MICHIGAN CITY IN TO NEW BUFFALO MI ATTN...WFO...IWX...
[edit] Example of a watch status message
STATUS REPORT #1 ON WW 600 VALID 160340Z - 160440Z THE SEVERE WEATHER THREAT CONTINUES ACROSS THE ENTIRE WATCH AREA. ..BRIGHT..08/16/07 ATTN...WFO...IWX... && STATUS REPORT FOR WT 600 SEVERE WEATHER THREAT CONTINUES FOR THE FOLLOWING AREAS INC001-003-009-017-033-039-049-053-069-075-085-087-091-099-103- 113-131-141-149-151-169-179-181-183-160440- IN . INDIANA COUNTIES INCLUDED ARE ADAMS ALLEN BLACKFORD CASS DE KALB ELKHART FULTON GRANT HUNTINGTON JAY KOSCIUSKO LAGRANGE LA PORTE MARSHALL MIAMI NOBLE PULASKI ST. JOSEPH STARKE STEUBEN WABASH WELLS WHITE WHITLEY $$ OHC003-039-051-069-125-137-161-171-160440- OH . OHIO COUNTIES INCLUDED ARE ALLEN DEFIANCE FULTON HENRY PAULDING PUTNAM VAN WERT WILLIAMS $$ LMZ046-160440- CW . ADJACENT COASTAL WATERS INCLUDED ARE MICHIGAN CITY IN TO NEW BUFFALO MI $$ THE WATCH STATUS MESSAGE IS FOR GUIDANCE PURPOSES ONLY. PLEASE REFER TO WATCH COUNTY NOTIFICATION STATEMENTS FOR OFFICIAL INFORMATION ON COUNTIES...INDEPENDENT CITIES AND MARINE ZONES CLEARED FROM SEVERE THUNDERSTORM AND TORNADO WATCHES. $$
[edit] See also
[edit] References
- ^ http://www.crh.noaa.gov/product_sites.php?site=ICT&product=WCN|Watch County Notification Messages
[edit] External links
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