Tornado watch

:"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.

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.

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.

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.

Example

Humboldt - Wynyard - Wadena - Lanigan - Foam Lake11:54 AM CST Wednesday 16 July 2008Tornado watch forHumboldt - Wynyard - Wadena - Lanigan - Foam Lake issued

Near Naicam a funnel cloud was spotted earlier this afternoon. Further funnel clouds are possible this afternoon.Some of these may produce weak tornadoes.

Conditions are favourable for the development of funnel clouds or weak tornadoes. These types of funnel clouds formout of large cumulus clouds or very weak thunderstorms and normally do not have the energy to reach the ground.However one or two of these funnels may briefly touch down and can become destructive over a very small area. Treatall funnel clouds and tornadoes seriously and avoid when possible. Should one develop overhead take shelter until itdissipates. Remember these funnel clouds will normally appear with little or no warning.

Environment Canada continues to monitor the situation closely. Please continue to monitor your local media orweatheradio for further updates.

Should you spot a funnel cloud or tornado...And only if it is safe to do so...You can call 1-800-239-0484 to reportyour sighting. Please note this phone number is for reporting severe weather only.

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). [http://www.crh.noaa.gov/product_sites.php?site=ICT&product=WCN|Watch County Notification Messages]

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

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...

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

$$THE WATCH STATUS MESSAGE IS FOR GUIDANCE PURPOSES ONLY. PLEASEREFER TO WATCH COUNTY NOTIFICATION STATEMENTS FOR OFFICIALINFORMATION ON COUNTIES...INDEPENDENT CITIES AND MARINE ZONESCLEARED FROM SEVERE THUNDERSTORM AND TORNADO WATCHES.$$

ee also

* Severe weather terminology (United States)
* Mesoscale discussion

References

External links

* [http://www.spc.noaa.gov/products/watch/ Current Watches]