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URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 557

NWS STORM PREDICTION CENTER NORMAN OK

105 PM CDT SUN JUN 26 2011



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       NORTH-CENTRAL NEBRASKA

       WESTERN AND CENTRAL SOUTH DAKOTA



EFFECTIVE THIS SUNDAY AFTERNOON AND EVENING FROM 105 PM UNTIL 800

PM CDT.



HAIL TO 2.5 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 105

STATUTE MILES EAST AND WEST OF A LINE FROM 25 MILES SOUTH

SOUTHEAST OF MULLEN NEBRASKA TO 40 MILES NORTH OF PIERRE SOUTH

DAKOTA.  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 555...WW 556...



DISCUSSION...COMPLEX SITUATION IS UNFOLDING TODAY WITH SCATTERED

STRONG-SEVERE TSTMS ONGOING FROM WRN/CNTRL SD INTO N-CNTRL NEB.

THIS ACTIVITY APPEARS TO BE ASSOCIATED WITH A LEAD SHORTWAVE TROUGH

PROGRESSING INTO THE WRN DAKOTAS AND ACTING ON A STEEP MIDLEVEL

LAPSE RATE ENVIRONMENT WITH MLCAPE OF 1000-2000 J/KG.  CONTINUED

BOUNDARY LAYER WARMING SHOULD ALLOW AMBIENT AIR MASS TO FURTHER

DESTABILIZE THIS AFTERNOON.  THIS INSTABILITY COMBINED WITH 40-50 KT

OF EFFECTIVE BULK SHEAR WILL BE MORE THAN SUFFICIENT TO SUPPORT

ORGANIZED STORM MODES INCLUDING SUPERCELLS AND BOWING STRUCTURES.

INITIAL HAZARDS ARE EXPECTED TO BE LARGE HAIL AND DAMAGING WINDS.

THE POTENTIAL FOR TORNADOES WILL INCREASE LATER TODAY AND PORTIONS

OF CURRENT WATCH AREA MAY NEED TO BE UPGRADED TO A TORNADO WATCH BY

MID/LATE AFTERNOON.



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

TO 2.5 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60

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

MOTION VECTOR 27030.





...MEAD

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