Area Forecast Discussion
Issued by NWS Rapid City, SD

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000
FXUS63 KUNR 250202
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
802 PM MDT THU JUL 24 2014

.UPDATE...
ISSUED AT 744 PM MDT THU JUL 24 2014

CURRENT SURFACE MAP PLACES COLD FRONT MOVING INTO SOUTHEAST
MONTANA. SMALL COMPLEX OF THUNDERSTORMS OVER NORTHWEST SOUTH
DAKOTA IS PRODUCING SOME DAMAGING WIND GUSTS. THUNDERSTORMS WILL
CONTINUE TO MOVE EAST THIS EVENING...WITH OUTFLOW BOUNDARY MOVING
THROUGH WESTERN SOUTH DAKOTA.

OBSERVATIONS ACROSS MONTANA SHOW WIND GUSTS 40-50KT ASSOCIATED
WITH COLD FRONT. 00Z NAM/RUC BRING AREA OF 6+MB/3HR PRESSURE RISES
THROUGH WESTERN SOUTH DAKOTA 06Z-09Z...WITH 40KT BL WINDS. HAVE
INCREASED FORECAST WINDS BEHIND FRONT...AND ISSUED WIND ADVISORY
FOR 45-55MPH GUSTS. POSSIBLE THAT RAPID CITY AREA EXCEEDS 60
MPH...THOUGH TIMING OF DAY NOT AS FAVORABLE. MAY NEED TO UPGRADE
TO HIGH WIND WARNING DEPENDING ON UPSTREAM TRENDS. THUNDERSTORM
ACTIVITY WILL DIMINISH THIS EVENING AS IT PUSHES EAST OF FORECAST
AREA

&&

.SHORT TERM...THIS EVENING THROUGH FRIDAY NIGHT ISSUED AT 216
PM MDT THU JUL 24 2014

POTENT NORTHERN STREAM UPPER TROUGH WILL ADVANCE EAST
ACROSS THE SOUTHERN CANADIAN PRAIRIE PROVINCES THROUGH THE
PERIOD...SUPPORTING A WEAK COLD FRONT AND ISOLD TS CHANCES TONIGHT
INTO THE FA. FAST WESTERLY FLOW ON THE SOUTHERN PERIPHERY OF THE
SK/MB UPPER VORTEX WILL SUPPORT RENEWED SHRA/TS CHANCES FRIDAY NIGHT
AS AN UPPER LEVEL JET STREAK ADVANCES SE ACROSS CENTRAL SD.

A STRONG CAPPING INVERSION REMAINS OVER MOST OF THE FA THIS
AFTERNOON...LIMITING ISOLD TS CHANCES SAVE FOR PERHAPS OVER NE WY
WHERE HIGH TERRAIN MIX OUT OF THE CAP IS EXPECTED. SLIGHTLY BETTER
CHANCES FOR PRECIP WILL DEVELOP THIS EVENING AND OVERNIGHT AS
STAUNCH CAPPING INVERSION BREAKS DOWN WITH HEIGHT FALLS SPREADING
SE PER THE NORTHERN STREAM UPPER TROUGH. FLOW EMBEDDED WEAK IMPULSES
ON THE SOUTHERN PERIPHERY OF THE UPPER TROUGH WILL EJECT NE OUT OF
WY AND SUPPORT ISOLD TS OVER MUCH OF THE FA...ESP THE SE HALF.
ACTIVITY MAY LINGER THROUGH MUCH OF THE NIGHT AS A LL THETA-E RIDGE
SLOWLY SETTLES SOUTH...INDICATED WELL AT H7. GIVEN STEEP MID LEVEL
LAPSE RATES/AMPLE LL MOISTURE/AND BROAD SCALE FORCING FOR
ASCENT...HAVE CARRIED TS CHANCES THROUGH MOST OF THE NIGHT PERIOD.
ANY ACTIVITY WILL BE HIGH BASED WITH POSSIBLE GUSTY WINDS GIVEN
STEEP LL LAPSE RATES. SOME HAIL IS POSSIBLE IN THE STRONGER CELLS.
DECENT PRESSURE RISES EXPECTED /4 MB PER HR/ WITH THE SFC COLD FRONT
LATE TONIGHT...LIKELY SUPPORTING A PERIOD OF GUSTY NW WINDS ACROSS
THE SD PLAINS IN CAA...ESP IN THE LEE OF THE BLACK HILLS. HAVE BUMPED
WINDS UP FOR THIS.

FRIDAY...DRIER AIR WILL ADVECT INTO THE REGION FRIDAY VIA BREEZY NW
WINDS WITH MOSTLY SUNNY SKIES. TEMPS WILL BE COOLER THAN TODAY MOST
PLACES...BUT STILL WARM WITH UPPER 80S AND LOW 90S EXPECTED. SK/MB
UPPER LOW WILL SHIFT SLOWLY EAST...AS AN UPPER LEVEL JET STREAK
POSITIONS OVER CENTRAL SD FRIDAY NIGHT. A SOUTHERN PERIPHERY IMPULSE
WILL SUPPORT A POS THETA-E ADV REGIME CENTERED AROUND H7 THROUGH
MUCH OF THE NIGHT SE HALF. LSA/UVM FROM THIS IMPULSE COUPLED WITH
LIFT AT AROUND THE RIGHT ENTRANCE REGION OF THE EXPECTED JET STREAK
SHOULD SUPPORT A DECENT CHANCE FOR SCT TS OVERNIGHT FRIDAY...ESP
OVER SCENTRAL SD. A FEW STRONGER STORMS WILL BE POSSIBLE GIVEN MU
CAPES OF 1000-1500 J/KG WITH EFFECTIVE SHEAR EXCESS OF 40 KNOTS.
DID RAISE POPS TO 30 WITH SOME 40S FAR SE. OTHERWISE...SLIGHTLY
COOLER OVERNIGHT LOWS WITH LOW 60S AND 50S COMMON.

&&

.LONG TERM...SATURDAY THROUGH THURSDAY
ISSUED AT 216 PM MDT THU JUL 24 2014

UPPER-LEVEL FLOW TRANSITIONS FROM ZONAL TO NORTHWESTERLY DURING THE
WEEKEND AS AN UPPER RIDGE REBUILDS OVER THE WESTERN CONUS. THIS WILL
RESULT IN COOLER TEMPERATURES AND MAINLY DRY CONDITIONS FROM
SATURDAY THROUGH MONDAY. WEAK SHORTWAVE DISTURBANCES WILL BEGIN TO
ROTATE AROUND THE WESTERN RIDGE AND INTO THE NORTHERN PLAINS AGAIN
BY THE MIDDLE OF NEXT WEEK. WILL CONTINUE WITH LOW CHANCE POPS
ACROSS PORTIONS OF THE AREA FROM MONDAY NIGHT THROUGH WEDNESDAY...
ESPECIALLY WESTERN AND SOUTHERN PORTIONS OF THE CWA.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z FRIDAY EVENING)
ISSUED AT 744 PM MDT THU JUL 24 2014

OUTSIDE OF THUNDERSTORMS...VFR CONDITIONS ARE EXPECTED. LCL MVFR
VSBY/CIGS EXPECTED WITH THUNDERSTORMS. A COLD FRONT WILL MOVE
THROUGH WESTERN SOUTH DAKOTA LATE THIS EVENING/OVERNIGHT WITH A
PERIOD OF STRONG NORTHWEST WINDS.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...WIND ADVISORY UNTIL 5 AM MDT FRIDAY FOR SDZ001-002-012-013-025-
     026-031-072-073.

WY...NONE.
&&

$$

UPDATE...7
SHORT TERM...JC
LONG TERM...26
AVIATION...7





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