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359 

WWUS20 KWNS 041904

SEL9

SPC WW 041904

IAZ000-MNZ000-NEZ000-SDZ000-050200-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 239

NWS STORM PREDICTION CENTER NORMAN OK

205 PM CDT FRI MAY 4 2012



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       NORTHWEST IOWA

       SOUTHWEST AND SOUTH-CENTRAL MINNESOTA

       NORTH-CENTRAL AND NORTHEAST NEBRASKA

       SOUTHEAST SOUTH DAKOTA



EFFECTIVE THIS FRIDAY AFTERNOON AND EVENING FROM 205 PM UNTIL 900

PM CDT.



HAIL TO 3 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 65

STATUTE MILES NORTH AND SOUTH OF A LINE FROM 45 MILES WEST OF

ONEILL NEBRASKA TO 35 MILES NORTH NORTHEAST OF MASON CITY IOWA.

FOR A COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH

OUTLINE UPDATE (WOUS64 KWNS WOU9).



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 238...



DISCUSSION...TSTMS ARE EXPECTED TO INCREASE IN NUMBER AND INTENSITY

THIS AFTERNOON INVOF STATIONARY BOUNDARY STRETCHING FROM SRN SD/NRN

NEB TO ALONG THE MN/IA BORDER.  AIR MASS ALONG/S OF THIS BOUNDARY IS

QUITE MOIST...AND WHEN COUPLED WITH STEEP MIDLEVEL LAPSE RATES AND

DAYTIME HEATING...EXPECT MLCAPE VALUES TO APPROACH 2000-3500 J/KG.

THE STRONGEST DEEP-LAYER SHEAR WILL REMAIN ALONG AND N OF SURFACE

FRONT WITH ENVIRONMENT SUPPORTIVE OF BOTH BOWING AND SUPERCELL

STRUCTURES.  WHILE A TORNADO IS POSSIBLE...VERY LARGE HAIL AND

DAMAGING WINDS WILL BE THE PRIMARY HAZARDS.



AVIATION...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 27030.





...MEAD

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