Editing Storm Prediction Center (section)

==Weather watches==
{{Main|Tornado watch|Severe thunderstorm watch}}
Watches (WWs) issued by the SPC are generally less than {{convert|20000|-|50000|sqmi|km2}} in area and are normally preceded by a mesoscale discussion.<ref name="watches"/> Watches are intended to be issued preceding the arrival of severe weather by one to six hours.<ref name="watches"/> They indicate that conditions are favorable for thunderstorms capable of producing various modes of severe weather, including large hail, damaging straight-line winds and/or tornadoes. In the case of [[severe thunderstorm watch]]es organized severe thunderstorms are expected but conditions are not thought to be especially favorable for tornadoes (although they can occur in such areas where one is in effect, and some severe thunderstorm watch statements issued by the SPC may note a threat of isolated tornadic activity if conditions are of modest favorability for storm rotation capable of inducing them), whereas for [[tornado watch]]es conditions are thought to be favorable for severe thunderstorms to produce tornadoes.<ref name="watches"/>

In situations where a forecaster expects a significant threat of extremely severe and life-threatening weather, a watch with special enhanced wording, "[[Particularly Dangerous Situation]]" (PDS), is subjectively issued.<ref name="PDS"/> It is occasionally issued with tornado watches, normally for the potential of major tornado outbreaks, especially those with a significant threat of multiple tornadoes capable of producing F4/EF4 and F5/EF5 damage and/or staying on the ground for long-duration – sometimes uninterrupted – paths.<ref name="PDS"/> A PDS severe thunderstorm watch is very rare and is typically reserved for derecho events impacting densely populated areas.<ref name="PDS"/>

Watches are not "warnings", where there is an immediate severe weather threat to life and property. Although [[severe thunderstorm warning|severe thunderstorm]] and [[tornado warning]]s are ideally the next step after watches, watches cover a threat of organized severe thunderstorms over a larger area and may not always precede a warning; watch "busts" do sometimes occur should thunderstorm activity not occur at all or that which does develop never reaches the originally forecast level of severity. Warnings are issued by local National Weather Service offices, not the Storm Prediction Center, which is a national guidance center.<ref name="watches"/>

The process of issuing a convective watch begins with a conference call from SPC to local NWS offices. If after collaboration a watch is deemed necessary, the Storm Prediction Center will issue a watch approximation product which is followed by the local NWS office issuing a specific county-based watch product. The latter product is responsible for triggering public alert messages via television, radio stations and NOAA Weather Radio. The watch approximation product outlines specific regions covered by the watch (including the approximate outlined area in [[statute mile]]s) and its time of expiration (based on the local [[time zone]](s) of the areas under the watch), associated potential threats, a meteorological synopsis of atmospheric conditions favorable for severe thunderstorm development, forecasted aviation conditions, and a pre-determined message informing the public of the meaning behind the watch and to be vigilant of any warnings or weather statements that may be issued by their local National Weather Service office.<ref name="watches"/>

Watch outline products provide a visual map depiction of the issued watch; the SPC typically delineates watches within this product in the form of "boxes", which technically are represented as either [[square]]s, [[rectangle]]s (horizontal or vertical) or [[parallelogram]]s depending on the area it covers. Jurisdictions outlined by the county-based watch product as being included in the watch area may differ from the actual watch box; as such, certain counties, parishes or boroughs not covered by the fringes of the watch box may actually be included in the watch and vice versa. Watches can be expanded, contracted (by removing jurisdictions where SPC and NWS forecasters no longer consider there to be a viable threat of severe weather, in which case, the watch box may take on a [[trapezoid]]al representation in map-based watch products) or canceled before their set time of expiration by local NWS offices.<ref name="watches"/>

===Example===
[[File:Ww2.gif|thumb|right|310px|Graphic associated with the example watch.<ref name="watch example"/>]]
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<pre>
URGENT - IMMEDIATE BROADCAST REQUESTED
   Tornado Watch Number 162
   NWS Storm Prediction Center Norman OK
   1005 AM CDT Wed Apr 26 2017

   The NWS Storm Prediction Center has issued a

   * Tornado Watch for portions of 
     Much of Arkansas
     Northwest Louisiana
     Northeast Texas

   * Effective this Wednesday morning and afternoon from 1005 AM
     until 500 PM CDT.

   * Primary threats include...
     A few tornadoes likely with a couple intense tornadoes possible
     Widespread large hail likely with isolated very large hail
       events to 2 inches in diameter possible
     Widespread damaging wind gusts to 70 mph likely

   SUMMARY...Severe storms will move across the watch area through this
   afternoon, posing a risk of locally damaging winds, large hail, and
   a few tornadoes.  An isolated strong tornado or two is also
   possible.

   The tornado watch area is approximately along and 90 statute miles
   east and west of a line from 25 miles north of Walnut Ridge AR to 35
   miles southeast of Longview TX. For a complete depiction of the
   watch see the associated watch outline update (WOUS64 KWNS WOU2).

   PRECAUTIONARY/PREPAREDNESS ACTIONS...

   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.

   &&

</pre>
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