A particularly dangerous situation (PDS) is a type of enhanced wording used by the National Weather Service's Storm Prediction Center in Norman, Oklahoma on certain weather watches. It implies that there is an enhanced risk of very severe and life-threatening weather, usually a major tornado outbreak or an extreme derecho.^[1] PDS watches are quite uncommon; less than 3% of watches issued by the SPC from 1996 to 2005 were PDS watches, or an average of 24 each year.^[2] The National Weather Service (NWS) is one of the six scientific agencies that make up the National Oceanic and Atmospheric Administration (NOAA) of the United States government. ... The Storm Prediction Center, located in Norman, Oklahoma, is part of the National Centers for Environmental Prediction (NCEP), operating under the control of the National Weather Service, which in turn is part of the National Oceanic and Atmospheric Administration (NOAA) of the U.S. government. ... Bizzell Library, University of Oklahoma Norman, Oklahoma, is the county seat and largest city in Cleveland County in the U.S. state of Oklahoma, and is part of the Oklahoma City Metropolitan Statistical Area. ... While there is no single agreed upon definition, generally more than six tornadoes in a day in the same region is considered a tornado outbreak. ... A derecho is a widespread and long-lived, violent convectively induced windstorm that is associated with a fast-moving band of severe thunderstorms usually taking the form of a bow echo. ... Year 1996 (MCMXCVI) was a leap year starting on Monday (link will display full 1996 Gregorian calendar). ... 2005 (MMV) was a common year starting on Saturday of the Gregorian calendar. ...

PDS tornado watches are issued when there is a greater risk of strong or violent tornadoes in the watch area, in addition to significant wind and hail damage. They are usually issued when the potential exists for a major tornado outbreak. They represent about 90% of PDS watches issued.^[3] A tornado watch is issued when weather conditions are favorable for the development of severe thunderstorms that are capable of producing tornados. ... A tornado in central Oklahoma. ... This article or section does not cite any references or sources. ... This does not cite any references or sources. ...

PDS severe thunderstorm watches are issued when there is a greater risk of severe wind damage capable of major structural damage (in addition to large hail and perhaps a few isolated tornadoes), usually due to a strong derecho. They are very rare (an average of only two each year^[4]) as the tornado risk has to remain low enough to only warrant a severe thunderstorm watch. Thunderstorm out flow from storm core shows up as sheets of wind driven rain spreading from right to left in 1982 photo. ...

These watches are typically issued after a high risk or an upper-end moderate risk of severe storms is issued by the SPC in the convective outlooks.

Sample PDS Tornado Watch

 URGENT - IMMEDIATE BROADCAST REQUESTED TORNADO WATCH NUMBER 239 NWS STORM PREDICTION CENTER NORMAN OK 905 PM CDT SAT MAY 5 2007 THE NWS STORM PREDICTION CENTER HAS ISSUED A TORNADO WATCH FOR PORTIONS OF MUCH OF KANSAS EFFECTIVE THIS SATURDAY NIGHT AND SUNDAY MORNING FROM 905 PM UNTIL 400 AM CDT. ...THIS IS A PARTICULARLY DANGEROUS SITUATION... DESTRUCTIVE TORNADOES...LARGE 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 115 STATUTE MILES EAST AND WEST OF A LINE FROM 30 MILES NORTH OF CONCORDIA KANSAS TO 20 MILES SOUTH OF MEDICINE LODGE KANSAS. FOR A COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU9). 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 232...WW 234...WW 235...WW 236...WW 237...WW 238... DISCUSSION...SUSTAINED SUPERCELLS EXPECTED TO PERSIST MOIST...HIGHLY-SHEARED ENVIRONMENT OVER THE CNTRL PLNS ON ERN SIDE OF 70+ KT SSWLY MID LEVEL SPEED MAX. WHILE ACTIVITY MAY CONGEAL INTO ONE OR MORE SEMI-LINEAR CLUSTERS...POTENTIAL WILL REMAIN FOR TORNADOES. OTHER STORMS MAY FORM LATER TONIGHT NEAR DRY LINE IN WRN PART OF WW...AND IN WARM ADVECTION ZONE OVER NE KS. 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 22040. ...CORFIDI 

References

1. ^ http://www.spc.noaa.gov/faq
2. ^ http://ams.confex.com/ams/23SLS/techprogram/paper_115252.htm
3. ^ http://ams.confex.com/ams/23SLS/techprogram/paper_115252.htm
4. ^ http://ams.confex.com/ams/23SLS/techprogram/paper_115252.htm

External links

• NOAA-NWS Storm Prediction Center