Hail and Damaging Winds in South Dakota, August 7, 2011

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
1005 AM MDT SUN AUG 7 2011

.DISCUSSION...CURRENT SURFACE ANALYSIS HAS HIGH PRESSURE CENTERED
OVER THE EASTERN DAKOTAS...WITH LOW PRESSURE OVER SOUTHEASTERN SK. A
COOL FRONT STRETCHES SOUTHWESTWARD FROM THE LOW ACROSS NORTHERN AND
WESTERN MT. UPPER LEVEL ANALYSIS SHOWS LOW PRESSURE OVER CENTRAL
AB...WITH ZONAL FROW FROM THE NORTHERN ROCKIES INTO THE NORTHERN
PLAINS. WATER VAPOR IMAGERY AND RUC ANALYSIS SHOWS WEAK IMBEDDED
ENERGY IN THE FLOW FROM THE ROCKIES INTO THE PLAINS. REGIONAL RADARS
SHOWING SCATTERED SHOWERS AND STORMS JUST SOUTH OF THE SD BORDER
ACROSS NORTH CENTRAL NEB...WITH ISOLATED SHOWERS AND STORMS OVER
NORTHWESTERN INTO CENTRAL SD. LOW CLOUDS AND PATCHY FOG COVER A GOOD
PORTION OF NORTHWEST INTO CENTRAL SD...BUT IS BEGINNING TO
DISSIPATE. TEMPS ARE IN THE 60S AND 70S ACROSS THE AREA...WARMEST IN
SUNNY AREAS.

AN ACTIVE LATE AFTERNOON AND EVENING IS LOOKING LIKELY FOR A GOOD
PORTION OF THE AREA AS COOL FRONT AND WEAK UPPER LEVEL ENERGY
APPROACH. THUNDERSTORMS ARE EXPECTED TO DEVELOP BY MID AFTERNOON
ACROSS WESTERN AREAS AS ATMOSPHERE DESTABILIZES AND SURFACE
TROF...AHEAD OF THE COLD FRONT...MOVES INTO NORTHEASTERN WY AND FAR
WESTERN SD. INSTABILITY WILL BE GREATEST AHEAD OF THE TROF...WITH
CAPE OF 1000 TO 2000 J/KG CONCENTRATED ACROSS THE BLACK HILLS AND
WESTERN SD. SHEAR WILL BE SUFFICIENT FOR SUPERCELLS...ESPECIALLY
FROM THE BLACK HILLS INTO SOUTHWESTERN SD AND NEB. THIS IS
WHERE THE BEST THREAT FOR SEVERE STORMS WILL BE...THOUGH ANYWHERE
FROM FAR NORTHEASTERN WY THROUGH CENTRAL SD WILL SEE A RISK FOR
SEVERE STORMS LATER THIS AFTERNOON INTO THE EVENING. LARGE HAIL AND
STRONG WIND GUSTS WILL BE THE MAIN THREATS FROM ANY SEVERE STORMS.
PRECIPITABLE WATER VALUES ARE ABOVE AVERAGE ACROSS MUCH OF WESTERN
AND SOUTH CENTRAL SD...SO THERE WILL ALSO BE A THREAT FOR LOCALLY
HEAVY RAIN.

WILL UPDATE FORECAST SHORTLY TO REMOVE FOG MENTION FOR THIS MORNING.
HAVE ALSO MADE ADJUSTMENTS TO CLOUD COVER FOR THE NEAR TERM AND
LOWERED HIGHS A BIT ACROSS EASTERN PORTIONS OF THE CWA.

PREVIOUS DISCUSSION...WATER VAPOR IMAGERY SHOWS NEAR ZONAL FLOW
ACROSS MUCH OF THE WESTERN AND CENTRAL CONUS WITH SEVERAL EMBEDDED
SHORTWAVES CROSSING THE REGION. SURFACE ANALYSIS SHOWS HIGH PRESSURE
ACROSS THE NORTHERN PLAINS WITH DEVELOPING LOW PRESSURE ACROSS
EASTERN MONTANA INTO NORTHEAST WYOMING.

TODAY...LOW PRESSURE WILL SET UP ALONG THE SD/WY BORDER. SOUTHERLY
FLOW WILL INCREASE ACROSS THE CWA...ESPECIALLY OVER THE SOUTH DAKOTA
PLAINS WHERE MOISTURE WILL BE BEST. MODELS ARE SHOWING MLCAPE OF
1500 TO 2000 J/KG...AND SUFFICIENT SHEAR FOR SOME STORMS TO BECOME
SEVERE. LARGE HAIL AND DAMAGE WINDS ARE THE MAIN THREATS. STORMS ARE
EXPECTED TO DEVELOP ACROSS THE BLACK HILLS BY MID AFTERNOON...AND
ACROSS THE PLAINS AFTERWARD. MOST OF THE STORMS SHOULD PUSH EAST OF
THE CWA BY 06Z TONIGHT AS A COOL FRONT PUSHES IN FROM THE NORTHWEST
OVERNIGHT.

HIGH PRESSURE WILL BUILD IN FROM THE WEST AS COOLER AIR FILTERS IN
MONDAY. DRIER WEATHER IS GENERALLY EXPECTED...HOWEVER SOME AREAS
COULD STILL SEE AN ISOLATED STORM OR TWO. TEMPERATURES MONDAY WILL
BE COOLER THAT TODAY...WITH HIGHS IN THE MID 70S TO MID 80S.

THE HIGH PRESSURE AXIS WILL CONTINUE TO DROP SOUTHEAST...CROSSING
THE AREA MONDAY NIGHT AND PUSHING EAST OF THE AREA TUESDAY MORNING.
RETURN FLOW WILL SET UP BRINGING BACK HIGHER THETA E TO THE CWA.
THERE WONT BE MUCH TIME FOR MOISTURE RECOVERY BEFORE DIURNAL HEATING
WANES LATE TUESDAY AFTERNOON...SO MOST AREAS WONT SEE MORE THAN
ISOLATED STORMS. BETTER CHANCES FOR STORMS ARE EXPECTED ACROSS THE
BLACK HILLS AND SOUTHWEST SOUTH DAKOTA WHERE MOISTURE ADVECTION WILL
BE BEST. COOLER TEMPERATURES WILL CONTINUE WITH HIGHS IN THE LOWER
70S TO LOWER 80S.

EXTENDED...ZONAL FLOW EXPECTED FOR WEDNESDAY/THURSDAY WITH SEVERAL
UPPER DISTURBANCES CROSSING THE AREA. THUNDERSTORMS POSSIBLE BOTH
DAYS. GFS/ECMWF ARE INDICATING THAT THE STRONGEST SHORTWAVE TROF
WILL MOVE THROUGH LATE THURSDAY. FOR FRIDAY INTO THE  WEEKEND...
ECMWF/GEFS SHOW INCREASING HEIGHTS AS UPPER LEVEL RIDGE BUILDS
ACROSS THE NORTHERN ROCKIES. THIS WILL RESULT IN A DRIER PATTERN.
TEMPERATURES WILL BE NEAR AVERAGE THROUGH THE EXTENDED.

&&

.AVIATION...AREAS OF MVFR/IFR CIGS WILL DISSIPATE BY 18Z OR SO
ACROSS NORTHWEST AND CENTRAL SOUTH DAKOTA. SCATTERED THUNDERSTORMS
WILL DEVELOP ACROSS WESTERN AREAS BY MID AFTERNOON AND MOVE
EASTWARD...WITH LCL IFR VSBY AND GUSTY WINDS. SOME OF THE STORMS MAY
BECOME SEVERE BY LATE THIS AFTERNOON AND PERSIST INTO THE EVENING.

&&

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

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE RAPID CITY SD
1230 PM MDT SUN AUG 7 2011

SDZ001-002-012>014-024>032-041>044-046-047-049-072>074-WYZ054>058-
071-081300-
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-
1230 PM MDT (130 PM CDT) SUN AUG 7 2011

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

.DAY ONE...TODAY AND TONIGHT

SCATTERED THUNDERSTORMS WILL CONTINUE THROUGH TONIGHT. THERE IS
A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON AND EVENING...
WITH LARGE HAIL AND DAMAGING WIND GUSTS POSSIBLE. LOCALLY HEAVY
RAINFALL IS ALSO EXPECTED WITH STORMS.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY

THERE IS A CHANCE OF THUNDERSTORMS MONDAY THROUGH THURSDAY.
THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS TUESDAY AFTERNOON AND
EVENING ACROSS SOUTHWEST SOUTH DAKOTA AND PARTS OF NORTHEAST
WYOMING. LARGE HAIL AND STRONG WIND GUSTS WILL BE THE MAIN THREATS
FROM ANY SEVERE STORMS.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE NEEDED TODAY.