

925 

WWUS20 KWNS 211926

SEL7

SPC WW 211926

IAZ000-NEZ000-220300-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 317

NWS STORM PREDICTION CENTER NORMAN OK

225 PM CDT SAT MAY 21 2011



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       WESTERN IOWA

       EASTERN NEBRASKA



EFFECTIVE THIS SATURDAY AFTERNOON AND EVENING FROM 225 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 55

STATUTE MILES EAST AND WEST OF A LINE FROM 20 MILES SOUTH

SOUTHEAST OF BEATRICE NEBRASKA TO 25 MILES NORTH NORTHEAST OF

SPENCER IOWA.  FOR A COMPLETE DEPICTION OF THE WATCH SEE THE

ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU7).



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.



OTHER WATCH INFORMATION...CONTINUE...WW 316...



DISCUSSION...TSTMS ARE DEVELOPING THIS AFTERNOON ALONG SURFACE

CONVERGENCE ZONE ASSOCIATED WITH MIDLEVEL VORTICITY MAXIMUM

TRANSLATING NEWD ACROSS REGION. AMBIENT AIR MASS IS MODERATELY

UNSTABLE WITH MLCAPE VALUES OF 1500-2000 J/KG AND LITTLE OR NO

CONVECTIVE INHIBITION.  VERTICAL SHEAR SHOULD INTENSIFY THROUGH LATE

AFTERNOON INTO EVENING AS MIDLEVEL FLOW STRENGTHENS...RESULTING IN A

KINEMATIC ENVIRONMENT SUPPORTIVE OF SUPERCELLS. GIVEN THE STEEP

LAPSE RATES AND COLD MID-TROPOSPHERIC TEMPERATURES...LARGE HAIL WILL

BE THE PRIMARY HAZARD WITH THE MOST INTENSE STORMS.



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 24020.





...MEAD

