

871 

WWUS20 KWNS 241947

SEL1

SPC WW 241947

NDZ000-250300-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 681

NWS STORM PREDICTION CENTER NORMAN OK

245 PM CDT SUN JUL 24 2011



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       CENTRAL AND SOUTHERN NORTH DAKOTA



EFFECTIVE THIS SUNDAY AFTERNOON AND EVENING FROM 245 PM UNTIL

1000 PM CDT.



HAIL TO 2 INCHES IN DIAMETER...THUNDERSTORM WIND GUSTS TO 70

MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS.



THE SEVERE THUNDERSTORM WATCH AREA IS APPROXIMATELY ALONG AND 60

STATUTE MILES NORTH AND SOUTH OF A LINE FROM 60 MILES WEST OF

DICKINSON NORTH DAKOTA TO 55 MILES SOUTH SOUTHEAST OF GRAND FORKS

NORTH DAKOTA.  FOR A COMPLETE DEPICTION OF THE WATCH SEE THE

ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU1).



REMEMBER...A SEVERE THUNDERSTORM WATCH MEANS CONDITIONS ARE

FAVORABLE FOR 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. SEVERE THUNDERSTORMS CAN AND OCCASIONALLY

DO PRODUCE TORNADOES.



DISCUSSION...TSTMS ARE DEVELOPING ALONG A WEAK SURFACE

BOUNDARY/CONFLUENCE AXIS WITH THIS ACTIVITY PERHAPS BEING AIDED BY A

WEAK MIDLEVEL IMPULSE TRANSLATING ACROSS NRN ND.  STRONG DAYTIME

HEATING COUPLED WITH BOUNDARY LAYER DEWPOINTS IN THE 60S IS

RESULTING A MODERATELY UNSTABLE AIR MASS THIS AFTERNOON WITH MLCAPE

VALUES ESTIMATED TO BE 1000-2000 J/KG.  OBSERVED AND FORECAST WIND

PROFILES EXHIBIT RELATIVELY WEAK LOW-LEVEL WINDS WITH 50+ KT WNWLY

FLOW IN THE MIDLEVELS.  RESULTANT DEEP-LAYER SHEAR IS MORE THAN

SUFFICIENT FOR SUPERCELL EVOLUTION WITH THE PRIMARY HAZARDS BEING

LARGE HAIL AND DAMAGING WIND GUSTS.



AVIATION...A FEW SEVERE THUNDERSTORMS WITH HAIL SURFACE AND ALOFT

TO 2 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60

KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 500. MEAN STORM

MOTION VECTOR 29030.





...MEAD

