Severe Thunderstorm Warning 375, NWS Rapid City, SD

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
234 PM MDT WED AUG 17 2011

.DISCUSSION...WATER VAPOR IMAGERY SHOWS A TROUGH ACROSS THE GREAT
LAKES WITH RIDGING OVER THE NORTHERN HIGH PLAINS INTO THE NORTHERN
ROCKIES. SURFACE ANALYSIS SHOWS HIGH PRESSURE ACROSS EASTERN SOUTH
DAKOTA INTO SOUTHERN MINNESOTA. SOUTHERLY RETURN FLOW ACROSS THE
WESTERN SOUTH DAKOTA PLAINS CONTINUES. SURFACE OBS AND RADAR SHOW A
DRY LINE STRETCHING ACROSS THE BLACK HILLS...WITH 57 DEGREE
DEWPOINTS OVER KUNR WHILE CUSTER AND GILLETTE WERE AT 35 AND 29
DEGREES RESPECTIVELY. RADAR ALSO SHOWING A SINGLE STORM JUST EAST OF
SUNDANCE WY NOW MOVING INTO LAWRENCE COUNTY SD. GOOD INSTABILITY
OVER THE SD PLAINS GIVEN THE RICH THETA E IN PLACE. MLCAPE OF 1500
TO 2000 J/KG EAST OF THE DRYLINE WITH THE CAP ERODING WILL BRING
CHANCES OF STORMS TO PARTS OF WESTERN SOUTH DAKOTA. SHEAR IS GOOD
ENOUGH FOR THE DEVELOPMENT OF SUPERCELLS. LARGE HAIL AND DAMAGING
WINDS ARE THE MAIN THREATS THROUGH THIS EVENING...WITH THE BEST
CHANCES ACROSS SOUTHWEST TO SOUTH CENTRAL SOUTH DAKOTA. VIS SAT
ALREADY SHOWS AN EXTENSIVE CU FIELD ACROSS CENTRAL SOUTH DAKOTA...SO
BESIDES CONVECTIVE INITIATION ALREADY TAKING OVER THE NORTHERN
HILLS...THINK THE NEXT STORMS WILL DEVELOP ALONG AND EAST OF THE
BADLANDS. THE DRYLINE WILL SLIDE EASTWARD THIS EVENING INTO CENTRAL
SOUTH DAKOTA...WITH THE STORMS EXITING THE CWA. MODELS HAVE BEEN
SHOWING LOW PRESSURE DEVELOPING ACROSS SOUTHWEST SD WHICH WOULD DRAW
HIGHER THETA E BACK INTO THE CWA. THIS COULD BRING ELEVATED
CONVECTION TO PARTS OF WESTERN SOUTH DAKOTA AFTER 06Z.

ZONAL TO WEAK CYCLONIC FLOW WILL DEVELOP AS AN UPPER TROUGH CROSSES
CENTRAL CANADA. A COLD FRONT WILL SLIDE THROUGH THURSDAY AFTERNOON
AND EVENING. THIS WILL PUSH THE BEST INSTABILITY EASTWARD INTO SOUTH
CENTRAL SD THROUGH THE DAY. HIGHS WILL REACH THE 80S TO LOWER 90S
ACROSS THE PLAINS. ZONAL FLOW WILL CONTINUE INTO FRIDAY WITH WEAK
EMBEDDED WAVES CROSSING THE AREA. CONFIDENCE IS LOWER ON STORM
POTENTIAL FRIDAY...BUT WITH THE PASSING WAVES WILL KEEP SLIGHT
CHANCE MENTION. TEMPERATURES WILL BE NOTICEABLY COOLER BEHIND THE
FRONT...WITH HIGHS IN THE LOWER 70S TO AROUND 80.

EXTENDED...A VARIETY OF WEAK SHORT WAVES MOVING THROUGH MAY BRING
SOME THUNDERSTORMS TO THE AREA THROUGH THE WEEKEND. OTHERWISE...DRY
WEATHER IS EXPECTED AS AN UPPER RIDGE REMAINS OVER THE REGION. NEAR
TO SLIGHTLY ABOVE AVERAGE TEMPERATURES ARE EXPECTED.

&&

.AVIATION...ISOLD/SCT TSTMS ARE POSSIBLE THROUGH TONIGHT MAINLY
FROM THE BLKHLS EWD. VFR CONDITIONS EXPECTED OUTSIDE OF ANY STRONGER
STORMS.

&&

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

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE RAPID CITY SD
647 AM MDT WED AUG 17 2011

SDZ001-002-012>014-024>032-041>044-046-047-049-072>074-WYZ054>058-
071-181300-
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-
647 AM MDT (747 AM CDT) WED AUG 17 2011

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

.DAY ONE...TODAY AND TONIGHT

THUNDERSTORMS ARE POSSIBLE THIS AFTERNOON AND INTO TONIGHT ACROSS
MUCH OF WESTERN AND SOUTH CENTRAL SOUTH DAKOTA. THERE IS A SLIGHT
RISK FOR SEVERE STORMS ACROSS SOUTHWESTERN SOUTH DAKOTA THIS
AFTERNOON...AND EASTWARD INTO SOUTH CENTRAL SOUTH DAKOTA THIS
EVENING. LARGE HAIL AND STRONG WIND GUSTS WILL BE THE MAIN THREATS
FROM ANY SEVERE STORMS. AN ISOLATED TORNADO IS ALSO POSSIBLE ACROSS
FAR SOUTHERN SOUTH DAKOTA...NEAR THE NEBRASKA BORDER.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

THERE WILL BE A DAILY CHANCE FOR THUNDERSTORMS ACROSS MUCH OF THE
AREA THROUGH SATURDAY. THERE IS A SLIGHT RISK FOR SEVERE STORMS
ACROSS PORTIONS OF SOUTHWESTERN AND SOUTH CENTRAL SOUTH DAKOTA ON
THURSDAY. LARGE HAIL AND STRONG WIND GUSTS WILL BE THE MAIN THREATS
FROM ANY SEVERE STORMS.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE NEEDED TODAY.

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