Tornado Warning 20, NWS Rapid City, SD

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
740 PM MDT WED JUL 8 2009

.DISCUSSION...CURRENT SURFACE ANALYSIS SHOWS LOW PRESSURE OVER
SOUTHWEST SD...WITH WARM FRONT EXTENDING EASTWARD INTO CENTRAL SD.
COLD FRONT IS MOVING INTO FAR WESTERN SD NOW...WITH OCCLUDED FRONT
EXTENDING NORTHWARD FROM THE LOW INTO WESTERN ND. LOCAL RADAR SHOWS
BULK OF ACTIVITY NOW EXTENDING FROM NORTHWEST INTO SOUTH CENTRAL SD.
ISOLATED SEVERE STORMS CONTINUE ACROSS EASTERN PORTIONS OF THE CWA.
REGIONAL RADARS SHOWING BULK OF SEVERE ACTIVITY IS NOW ACROSS FAR
EASTERN MT INTO WESTERN ND.

HAVE EXTENDED THE TORNADO WATCH TO COVER SOUTH CENTRAL SD FOR THE
NEXT COUPLE OF HOURS. THE THREAT IS THERE FOR AN ISOLATED TORNADO
ACROSS THE REMAINING AREAS IN THE WATCH...BUT THE MAIN THREATS LOOK
TO BE STRONG WIND GUSTS AND POSSIBLY SOME LARGE HAIL. LOOKS LIKE
SEVERE ACTIVITY WILL WIND DOWN LATE THIS EVENING AS ACTIVITY MOVES
NORTH AND EAST OUT OF THE CWA. HAVE KEPT ISOLATED STORMS IN THE
FORECAST THROUGH THE EVENING FOR AREAS FURTHER WEST AS WEAKER ENERGY
AND THE COLD FRONT CROSS THE AREA. STILL LOOKS LIKE SOME GUSTY
NORTHWEST WINDS WILL DEVELOP LATER THIS EVENING BEHIND THE FRONTAL
PASSAGE ACROSS NORTHWEST AND WEST CENTRAL SD AND LAST FOR A FEW
HOURS.

UPDATED GRIDS AND ZONES HAVE BEEN SENT FOR THE TIME BEING. THEY WILL
NEED TO BE UPDATED LATER THIS EVENING TO CANCEL THE WATCH AND MODIFY
POPS.

PREVIOUS DISCUSSION...CURRENT SURFACE ANALYSIS SHOWS LOW PRESSURE
OVER NORTHEASTERN WY...WITH WARM FRONT STRETCHING EASTWARD INTO
SOUTHERN SD. SURF TROF EXTENDS NORTH FROM THE LOW INTO SOUTHEAST MT
AND COOL FRONT TRAILS WESTWARD ACROSS CENTRAL WY. UPPER LEVEL
ANALYSIS SHOWS RIDGING OVER THE NORTHERN PLAINS...WITH UPPER LOW
OVER THE PACIFIC NORTHWEST. SOUTHWESTERLY FLOW ALOFT IS IN PLACE
FROM THE GREAT BASIN AREA INTO THE NORTHERN HIGH PLAINS...WITH
STRONG JET MOVING NORTHEASTWARD ACROSS THE REGION. ABUNDANT LOW
LEVEL MOISTURE IS IN PLACE ALONG AND NORTH OF THE WARM FRONT ACROSS
WESTERN SD. TEMPS ARE IN THE 70S AND 80S. KUDX RADAR SHOWS A COUPLE
OF CELLS OVER SOUTHERN CAMPBELL CO...WITH CUMULUS BEGINNING TO BUILD
OVER THE HILLS...AS WELL AS ALONG A SURFACE TROF OVER NORTHEAST WY.

AN ACTIVE LATE AFTERNOON AND EVENING LOOKS TO BE ON TAP FOR PORTIONS
OF THE AREA...ESPECIALLY THE NORTHERN HALF OF THE CWA...AS SHORTWAVE
ENERGY...MID AND UPPER LEVEL JETS...AND FRONTAL BOUNDARY INTERACT.
WARM FRONT WILL SLOWLY LIFT NORTH AND EAST ACROSS THE SD PLAINS AS
LOW MOVES INTO THE BLACK HILLS AREA LATER THIS AFTERNOON. BEST
INSTABILITY WILL BE FROM THE BLACK HILLS AREA...NORTH AND
EAST...LATER THIS AFTERNOON INTO THE EVENING. SHEAR WILL BE RATHER
IMPRESSIVE...SUPPORTING SUPERCELL DEVELOPMENT. LARGE HAIL AND STRONG
WIND GUSTS WILL BE THE MAIN THREATS...WITH WIND LIKELY BECOMING THE
GREATER THREAT DURING THE EVENING AS A POSSIBLE BOW ECHO OR DERECHO
EVENT COULD DEVELOP. TORNADIC THREAT WILL BE GREATEST NORTH AND EAST
OF THE LOW AND WARM FRONT...PRIMARILY ACROSS NORTHWESTERN SD. LOW
PRESSURE AND COOL FRONT WILL PUSH EAST ACROSS THE AREA
TONIGHT...WITH GUSTY NORTHWEST WINDS FOR A WHILE BEHIND IT. LOWS
WILL BE IN THE 50S AND LOWER 60S.

THURSDAY AND FRIDAY WILL MAINLY BE DRY DAYS. HOWEVER...CANNOT RULE
OUT A FEW SHOWERS AND STORMS LATE THURSDAY NIGHT AND FRIDAY AS WEAK
ENERGY CROSSES THE REGION. HIGHS EACH DAY WILL GENERALLY BE IN THE
MID 70S TO MID 80S.

EXTENDED...UPPER RIDGE WILL REMAIN ACRS SRN CONUS FROM ARIZONA
THROUGH TEXAS DURING THE EXTENDED PERIOD. THIS WILL KEEP NRN PLAINS
ON NRN FRINGES OF UPPER RIDGE WITH OCCASIONAL S/WS MVG THRU THE
UPPER FLOW BRINGING A DAILY CHC OF SHOWERS AND TSTMS TO THE REGION.
TEMPERATURES WILL REMAIN NEAR SEASONAL NORMALS THRU THE PERIOD.

&&

.AVIATION...SCT THUNDERSTORMS...A FEW STRONG TO SEVERE...WILL
CONTINUE ACROSS NORTHWEST THROUGH CENTRAL SD THROUGH THE
EVENING...WITH ISOLATED ACTIVITY STILL POSSIBLE AFTER 06Z. BRIEF
PERIODS OF MVFR/IFR CONDITIONS ARE POSSIBLE. ELSEWHERE...ISOLATED
SHOWERS AND STORMS ARE POSSIBLE THROUGH LATE EVENING. CONDITIONS
WILL GENERALLY BECOME VFR EVERYWHERE AFTER 06Z.

&&

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

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE RAPID CITY SD
647 AM MDT WED JUL 8 2009

SDZ001-002-012>014-024>032-041>044-046-047-049-072>074-WYZ054>058-
071-091300-
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 JUL 8 2009

...MODERATE RISK OF SEVERE THUNDERSTORMS OVER FAR NORTHWESTERN SOUTH
DAKOTA...

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

.DAY ONE...TODAY AND TONIGHT

A STRONG UPPER LEVEL DISTURBANCE WILL MOVE ACROSS THE REGION LATER
TODAY AND TONIGHT. THUNDERSTORMS ARE EXPECTED TO DEVELOP OVER THE
HIGHER TERRAIN OF WYOMING AND THE BLACK HILLS IN THE AFTERNOON
THEN MOVE EAST ONTO THE SOUTH DAKOTA PLAINS LATER THIS
AFTERNOON AND TONIGHT. THERE IS A MODERATE RISK OF SEVERE
THUNDERSTORMS OVER FAR NORTHWEST SOUTH DAKOTA...WITH A SLIGHT RISK
FOR SEVERE THUNDERSTORMS ACROSS MOST OF NORTHEAST WYOMING AND
THE REMAINDER OF WESTERN SOUTH DAKOTA WITH VERY LARGE HAIL AND
DAMAGING WIND GUSTS POSSIBLE. IN ADDITION...A FEW TORNADOES
ARE POSSIBLE ACROSS NORTHWEST SOUTH DAKOTA GENERALLY NORTH OF
INTERSTATE 90. THUNDERSTORMS SHOULD PUSH EAST OF OUR AREA BY OR
SHORTLY AFTER MIDNIGHT.

TAKE TIME TO REVIEW YOUR SEVERE WEATHER PLANS AND PREPARE FOR
HAZARDOUS CONDITIONS BEFORE STORMS DEVELOP. MONITOR NOAA WEATHER
RADIO OR LOCAL MEDIA FOR UPDATED INFORMATION ON THIS POTENTIAL
SEVERE WEATHER OUTBREAK.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

THE PROBABILITY FOR WIDESPREAD HAZARDOUS WEATHER IS LOW.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE NEEDED TODAY...ESPECIALLY ACROSS
NORTHWEST SOUTH DAKOTA.

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