Severe Thunderstorm Warning 243, NWS Rapid City, SD

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
225 PM MDT WED JUL 27 2011

.DISCUSSION...20Z SURFACE MAP SHOWS WEAK FRONTAL BOUNDARY HAS
MOVED ACROSS MOST OF WRN SD WITH A WEAK ENE SURFACE UPSLOPE FLOW
DEVELOPING ACROSS WRN SD. SKIES ARE MOSTLY CLEAR WITH CUMULUS NOW
DEVELOPING ACROSS THE BLACK HILLS. EXPECT SCT TSTMS TO DEVELOP OVER
THE BLACK HILLS SOON.

TONIGHT...HEATING WILL PRODUCE CAPE OF 1000-2000 J/KG FM BLACK
HILLS EAST THRU SOUTH CENTRAL SD. WIND PROFILES ARE SUPPORTIVE OF
SUPERCELL FORMATION. CAPE/SHEAR/INSTABILITY WILL COMBINE WITH AN
APPROACHING WEAK UPPER DISTURBANCE TO PRODUCE SCATTERED TSTMS THIS
AFT/TONIGHT. EXPECT INITIAL STORMS LATER THIS AFT ACROSS BLACK
HILLS DUE TO WEAK UPSLOPE FLOW ACROSS REGION. STORMS SHOULD MOVE
EAST OFF BLK HLS AND ACROSS PLAINS THIS EVENING. MAIN THREATS
SHOULD BE LARGE HAIL/DAMAGING WINDS.

THURS/THURS NITE...OVERNIGHT CONVECTION MAY STILL BE ON GOING
ACROSS WRN SD PLAINS AHEAD OF UPPER DISTURBANCE MOVING INTO WRN
SD DURING THE MORNING HOURS. EXPECT PLENTY OF EARLY CLOUD COVER
OVER WRN SD PLAINS DURING AM HOURS WITH BEST HEATING ACROSS NERN
WY/FAR WRN SD. WEAK UPSLOPE FLOW WILL CONTINUE ACROSS THE REGION
WITH PLENTY OF MOISTURE AVAILABLE. DESPITE LACK OF UPPER SUPPORT
THURSDAY AFT EXPECT SCT TSTMS TO AGAIN DEVELOP...LIKELY NEAR OR
ALONG BLACK HILLS AIDED BY WEAK UPSLOPE FLOW. AGAIN WIND PROFILES
WILL SUPPORT SUPERCELL FORMATION.

FRI/FRI NIGHT...WEAK UPPER DISTURBANCE WILL MOVE ACROSS THE
REGION AND COMBINE WITH A MOIST ESE UPSLOPE FLOW/CAPE IN 1500-2500
J/KG RANGE AND MODERATE INSTABILITY TO PRODUCE SCT TSTMS AGAIN.
WIND PROFILES AGAIN SUPPORTIVE OF SUPERCELL DEVELOPMENT. EXPECT
THESE STORMS TO CONTINUE INTO FRIDAY EVENING.

EXTENDED...ZONAL FLOW WILL TRANSITION TO AN UPPER LEVEL RIDGE OVER
THE PLAINS FOR THE BEGINNING OF NEXT WEEK. THO MOST OF THE AREA WILL
BE DRY...WEAK LEE TROF WILL PROVIDE SURFACE CONVERGENCE...AND WEAK
SHORT WAVES CROSSING THE RIDGE MAY TRIGGER ISOLATED THUNDERSTORMS.
AS RIDGE SHIFTS EASTWARD...SOUTHWEST FLOW WILL BRING STRONGER
IMPULSES...AND COMBINED WITH A COLD FRONT DROPPING ACROSS THE
FORECAST AREA...PRODUCE SCATTERED STORMS MONDAY AFTERNOON AND
EVENING. TEMPERATURES WILL BE ABOVE SEASONAL AVERAGES THROUGH
MONDAY...THEN COOL A FEW DEGREES TUESDAY BEHIND THE COLD FRONT.

&&

.AVIATION...ISOLATED THUNDERSTORMS WILL DEVELOP THIS AFTERNOON AND
EVENING...WITH STRONG TO SEVERE STORMS POSSIBLE OVER THE BLACK
HILLS ACROSS SOUTHWESTERN SOUTH DAKOTA. UPSLOPE WINDS WILL PRODUCE
BKN-OVC040-060 CIGS...AND POSSIBLE MVFR CIGS...LATE TONITE-EARLY
MORNING...ESPECIALLY OVER NERN WY TO ERN SLOPES OF THE BLK HLS.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...NONE.
WY...NONE.

&&

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE RAPID CITY SD
1030 AM MDT WED JUL 27 2011

SDZ001-002-012>014-024>032-041>044-046-047-049-072>074-WYZ054>058-
071-281300-
BENNETT-BUTTE-CENTRAL BLACK HILLS-CUSTER CO PLAINS-FALL RIVER-HAAKON-
HARDING-HERMOSA FOOT HILLS-JACKSON-MELLETTE-NORTHEASTERN CROOK-
NORTHERN BLACK HILLS-NORTHERN CAMPBELL-NORTHERN FOOT HILLS-
NORTHERN MEADE CO PLAINS-PENNINGTON CO PLAINS-PERKINS-RAPID CITY-
SHANNON-SOUTHERN BLACK HILLS-SOUTHERN CAMPBELL-SOUTHERN FOOT HILLS-
SOUTHERN MEADE CO PLAINS-STURGIS/PIEDMONT FOOT HILLS-TODD-TRIPP-
WESTERN CROOK-WESTON-WYOMING BLACK HILLS-ZIEBACH-
1030 AM MDT (1130 AM CDT) WED JUL 27 2011

THIS HAZARDOUS WEATHER OUTLOOK IS FOR WESTERN SOUTH DAKOTA AND
NORTHEASTERN WYOMING.

.DAY ONE...TODAY AND TONIGHT

THERE IS A SLIGHT RISK FOR SEVERE THUNDERSTORMS FROM EXTREME
NORTHEASTERN WYOMING ACROSS WESTERN AND SOUTH CENTRAL SOUTH DAKOTA
THIS AFTERNOON AND TONIGHT. LARGE HAIL AND DAMAGING WIND GUSTS WILL
BE THE MAIN THREATS.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

A SLIGHT RISK OF SEVERE THUNDERSTORMS IS FORECAST FOR WESTERN AND
CENTRAL SOUTH DAKOTA BOTH THURSDAY AND FRIDAY...WITH LARGE HAIL AND
DAMAGING WIND GUSTS THE MAIN THREATS.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE NEEDED TODAY.

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