Damaging Wind in South Dakota, June 21, 2010

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
831 PM MDT MON JUN 21 2010

.DISCUSSION...02Z SFC ANALYSIS SHOWS LOW PRESSURE OVER
NORTHEASTERN WYOMING WITH A TROUGH EXTENDING FROM NORTH OF KGCC
INTO SOUTHWESTERN NORTH DAKOTA. STRONG TO SEVERE THUNDERSTORMS
HAVE DEVELOPED NORTH AND EAST OF THE LOW THIS EVENING.
THUNDERSTORM CLUSTER CURRENTLY LOCATED IN SERN MONTANA WILL
CONTINUE TO SHIFT EASTWARD THIS EVENING INTO NORTHWESTERN SOUTH
DAKOTA...WITH MORE THUNDERSTORMS MOVING INTO SOUTHWESTERN SOUTH
DAKOTA FROM WYOMING AND NEBRASKA. THUNDERSTORM THREAT FOR
NORTHEASTERN WYOMING FOR CAMPBELL AND WESTON COUNTIES IN WYOMING
WILL END SHORTLY...CONTINUING FOR A COUPLE MORE HOURS IN FAR
NORTHERN CROOK COUNTY.

&&

.AVIATION...SCATTERED STRONG TO SEVERE THUNDERSTORMS WILL CONTINUE OVER
WESTERN SOUTH DAKOTA THIS EVENING...ENDING IN ANOTHER HOUR OR TWO
OR NORTHEASTERN WYOMING. AREAS OF MVFR CIGS MAY DEVELOP AFTER
MIDNIGHT OVER PARTS OF NORTHEASTERN WYOMING AND NORTHWESTERN SOUTH
DAKOTA.

&&

.PREV DISCUSSION... /ISSUED 130 PM MDT MON JUN 21 2010/

DISCUSSION...CURRENT SURFACE ANALYSIS PLACES TROF OVER EASTERN
WYOMING WHILE RIDGE REMAINS OVER THE EASTERN CONUS. UPPER LEVEL
ANALYSIS PLACES COMPACT LOW OVER EASTERN MONTANA...BRINGING
WEST/SOUTHWESTERLY FLOW ALOFT TO THE AREA. A FEW STORMS ARE NOW
DEVELOPING OVER THE BLACK HILLS.

FOR THE REST OF THE AFTERNOON/TONIGHT...A FEW THUNDERSTORMS WILL
CONTINUE TO DEVELOP WITH THE ACTIVITY OVER THE BLACK HILLS...BUT THE
BETTER CHANCE COMES MORE TOWARDS LATE AFTERNOON/EARLY EVE SPREADING
FROM WEST TO EAST ACROSS THE CWFA. INSTABILITY CONTINUES TO BE
STRONG OVER THE AREA...WITH THE GREATEST SHEAR OVER NORTHWEST SOUTH
DAKOTA INTO NORTHEAST WYOMING. LARGE HAIL/DAMAGING WIND GUSTS
CONTINUE TO BE THE GREATEST THREATS...THOUGH A TORNADO THREAT DOES
EXIST LATE AFT/EARLY EVE INVOF SURFACE TROF OVER NE WYO PUSHING INTO
THE BLKHLS/NWRN SODAK. STORMS WILL PUSH EAST THROUGH THE EVENING.

ON TUESDAY...WEAK COOL FRONT SLIDES INTO THE AREA EARLY IN THE
DAY...BRINGING COOLER TEMPS TO THE NORTHWESTERN CWFA. EXPECT
THUNDERSTORMS TO AGAIN DEVELOP IN THE AFTERNOON...WITH THE GREATEST
SEVERE THREAT OVER THE SOUTHEASTERN CWFA...WHERE MODELS BRING ABOUT
2-3 KJ/KG OF CAPE AND PLENTY OF SHEAR TO SUPPORT ROTATING STORMS.
STORMS WILL CONTINUE THROUGH THE EVENING BEFORE TAPERING OFF FROM
WEST TO EAST OVERNIGHT.

FOR WEDNESDAY...QUIETER WEATHER IS EXPECTED AS SHORTWAVE RIDGE
BUILDS OVER THE AREA.

EXTENDED...A WEAK UPPER LEVEL RIDGE WILL SLIDE EAST OF THE AREA
THURSDAY...BRINGING A RETURN TO SOUTHWESTERLY FLOW ALOFT.
DISTURBANCES IN THE UPPER FLOW WILL RESULT IN A SLIGHT CHANCE OF
MAINLY AFTERNOON AND EVENING THUNDERSTORMS NEARLY EVERY DAY. HIGH
TEMPERATURES WILL GENERALLY BE IN THE 80S.

&&

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

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE RAPID CITY SD
635 AM MDT MON JUN 21 2010

SDZ001-002-012>014-024>032-041>044-046-047-049-072>074-WYZ054>058-
071-221300-
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-
635 AM MDT (735 AM CDT) MON JUN 21 2010

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

.DAY ONE...TODAY AND TONIGHT

SCATTERED THUNDERSTORMS WILL DEVELOP ACROSS THE AREA THIS
AFTERNOON AND TONIGHT. THERE IS A SLIGHT RISK FOR SEVERE
THUNDERSTORMS ACROSS THE ENTIRE AREA LATE THIS AFTERNOON AND
EVENING. AT THIS TIME...THE BEST CHANCE FOR SEVERE STORMS LOOKS TO BE
FROM FAR NORTHEASTERN WYOMING INTO NORTHWESTERN SOUTH DAKOTA. THE
MAIN THREATS FROM ANY SEVERE STORMS WILL BE LARGE HAIL AND STRONG
WIND GUSTS...BUT AN ISOLATED TORNADO IS ALSO POSSIBLE...ESPECIALLY
FROM NORTHEASTERN WYOMING INTO NORTHWESTERN SOUTH DAKOTA. STORMS WILL
MOVE EAST OF THE AREA DURING THE OVERNIGHT.

.DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY

THERE IS A SLIGHT RISK FOR SEVERE THUNDERSTORMS ACROSS MOST OF
NORTHEASTERN WYOMING AND WESTERN SOUTH DAKOTA TUESDAY AFTERNOON AND
EVENING. LARGE HAIL AND STRONG WIND GUSTS WILL BE THE MAIN THREATS
FROM ANY SEVERE STORMS.

AFTER A BRIEF BREAK ON WEDNESDAY...THE CHANCES FOR THUNDERSTORMS
WILL RETURN TO THE AREA DURING THE LATTER PART OF THE WEEK.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE NEEDED TODAY.

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