Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 181747
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
1147 AM MDT THU SEP 18 2014

.SHORT TERM...TODAY THROUGH FRIDAY NIGHT
ISSUED AT 231 AM MDT THU SEP 18 2014

RIDGE FLATTENING DISTURBANCE WILL PUSH THROUGH THE REGION IN THE
PERIOD...SUPPORTING WARM CONDITIONS WITH A SLIGHT CHANCE FOR A
SHRA/TS. MASSIVE WESTERN CONUS RIDGE WILL SHIFT EAST TODAY...WITH
THE ASSOCIATED THERMAL RIDGE ADVECTING OVER THE FA TODAY. WEAK POS
THETA-E ADV COMBINED WITH STEEP MID LEVEL LAPSE RATES AND AMPLE
MID LEVEL MOISTURE HAS SUPPORTED A FEW SHRA/TS EARLIER OVER THE
EASTERN FA. ASSOCIATED FORCING WILL TREND EAST OF THE FA AS THE
RIDGE BUILDS EAST...ENDING ANY PRECIP CHANCES BEFORE DAWN MOST
PLACES. OTHERWISE...UPPER LEVEL RIDGING WILL BE ONGOING INTO THIS
AFTERNOON AHEAD OF THE PAC NW SHORTWAVE TROUGH. THIS TROUGH WILL
PUSH INTO THE REGION THIS EVENING AND SUPPORT EJECTION OF THE LEE
SIDE TROUGH IN PLACE...WITH SLIGHT CHANCES FOR SHOWERS AND TS
SPREADING NW TO SE ACROSS THE FA THROUGH FRIDAY.

TODAY/TONIGHT...DRY WEATHER EXPECTED TODAY WITH WEAK SHORTWAVE
RIDGING THROUGH THIS AFTERNOON. THERMAL RIDGE WILL TIME OVER THE
REGION AT PEAK HEATING...SUPPORTING WARM TEMPS MOST PLACES...WITH
80S AND 90S EXPECTED. BREEZY SOUTHERLY WINDS EXPECTED GIVEN ONGOING
SFC PRESSURE FALLS AND ASSOCIATED GRADIENT FLOW...BREEZIEST OVER
SCENTRAL SD. UPPER LEVEL TROUGH AND ASSOCIATED JET STREAK WILL
APPROACH THE REGION THIS EVENING...WITH A LL THETA-E RIDGE
PRESENT....MAINLY ACROSS THE NORTHERN ZONES. ISOLD TO SCT CONVECTION
WILL PUSH INTO THE NW ZONES THIS EVENING...WITH THE BEST CHANCE FOR
ANY ACTIVITY OVER THE FAR NW SD ZONES THROUGH TONIGHT. GIVEN ML
CAPES AOA 1000 J/KG WITH BULK 0-6KM SHEAR IN EXCESS OF 40 KNOTS...A
FEW STRONGER CELLS ARE VERY WELL POSSIBLE OVER NW SD. WARM OVERNIGHT
LOWS EXPECTED MOST PLACES GIVEN PARTIALLY MIXED BL WITH WARM THERMAL
FIELDS...ESP IN LEE OF THE BLACK HILLS WHERE TERRAIN INDUCED
DOWNSLOPING IS EXPECTED PER PRESSURE FALLS.

FRIDAY...LL THETA-E RIDGE AND ASSOCIATED LL TROUGH WILL SHIFT SE
ACROSS THE FA WITH SLIGHT CHANCES FOR SHRA/TS AOA THIS FEATURE GIVEN
SYNOPTIC FORCING AND INSTABILITY. NOT TOO EXCITED ABOUT PRECIP
CHANCES GIVEN LACK OF APPRECIABLE UPPER LEVEL FORCING WITH THE BULK
OF LSA PASSING NORTH OF THE FA. HENCE...RELEGATED POPS TO SLIGHT
CHANCE OUTSIDE THE BLACK HILLS. COOLER CONDITIONS EXPECTED WESTERN
HALF WITH CAA ONGOING THERE. LL THETA-E RIDGE WILL SLOWLY SHIFT
SOUTH THROUGH FRIDAY NIGHT WITH LINGERING CHANCES FOR SHRA/TS...ESP
AS ANOTHER JET STREAK PUSHES SE INTO THE NORTHERN PLAINS AND FORCES
ADDITIONAL LSA. RETAINED LOW POPS ACROSS THE FAR SOUTH THROUGH MUCH
OF FRIDAY NIGHT FOR THIS. COOLER CONDITIONS EXPECTED ALL PLACES WITH
CAA ONGOING ACROSS THE FA.

&&

.LONG TERM...SATURDAY THROUGH WEDNESDAY
ISSUED AT 231 AM MDT THU SEP 18 2014

UPPER LEVEL TROF QUICKLY SHIFTS EAST AS ANOTHER UPPER RIDGE OVER THE
WESTERN CONUS REBUILDS. NORTHWEST FLOW OVER THE FORECAST AREA WILL
KEEP CONDITIONS DRY FOR THE WEEKEND WITH SEASONAL TEMPERATURES.
MEDIUM RANGE MODEL SOLUTIONS FOR NEXT WEEK BRING A WEAK CUT-OFF LOW
INTO THE CENTRAL PLAINS LATE MONDAY INTO TUESDAY. SURFACE HIGH
SHIFTS EAST DURING THIS TIME...SO SOUTHERLY RETURN FLOW SHOULD BRING
SOME MOISTURE BACK INTO THE AREA. THIS COMBINATION SHOULD BRING AT
LEAST A SMALL CHANCE FOR SOME SHOWERS AND THUNDERSTORMS TO PARTS OF
THE AREA FOR MONDAY AFTERNOON INTO TUESDAY. TEMPERATURES SHOULD
REMAIN CLOSE TO SEASONAL AVERAGES THROUGH MUCH OF NEXT WEEK.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z FRIDAY)
ISSUED AT 1146 AM MDT THU SEP 18 2014

LOW LEVEL JET WILL DEVELOP ACROSS THE WRN SD PLAINS THIS EVENING
AND CONTINUE OVERNIGHT. A COLD FRONT WILL CROSS THE AREA LATE
TONIGHT/EARLY FRI MORNING WITH GUSTY NW WINDS BEHIND THE FRONT.
SOME ISOLATED -SHRA/-TSRA ARE POSSIBLE WITH THE FRONTAL PASSAGE
WITH MVFR CONDITIONS IN ANY HEAVY SHOWERS. OTHERWISE VFR
CONDITIONS ARE EXPECTED THROUGH FRIDAY.

&&

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

$$

SHORT TERM...JC
LONG TERM...15
AVIATION...13





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