WATCHES: Severe Thunderstorm Watch Number 317

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

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