Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 291123
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
523 AM MDT FRI AUG 29 2014

.SHORT TERM...TODAY THROUGH SATURDAY NIGHT
ISSUED AT 251 AM MDT FRI AUG 29 2014

STRONG SHORTWAVE TROUGH IS CROSSING THE CENTRAL PLAINS INTO THE ERN
DAKOTAS TO UPPER MIDWEST. ZONAL FLOW SITS ACROSS THE WRN CONUS WITH
A MUCH WEAK SHORTWAVE CROSS CNTRL/ERN MT. SURROUNDING RADAR SITES
SHOWING -SHRA/TSRA CROSSING ERN MT TO NRN WY. A SURFACE COLD FRONT
ALSO ASSOCIATED WITH THE WAVE/PRECIP IS SLIDING SE AND IS VISIBLE ON
THE BIS/BYZ RADARS.

COLD FRONT/UPPER WAVE WILL QUICKLY PUSH THROUGH THE CWA TODAY
BRINGING CHANCES FOR -SHRA/TSRA. LATEST TIMING APPEARS TO HAVE THE
AREA OF PRECIP OVER THE BLKHLS AREA BY LATE MORNING...THE CONTINUING
EWD INTO THE WRN SD PLAINS THROUGH THE AFTERNOON. STRONG INSTABILITY
DEVELOPING AHEAD OF THE FRONT OVER WRN/CNTRL SD PLAINS COULD RESULT
IN SOME STRONG STORMS THIS AFTERNOON...BUT SHEAR WILL BE QUITE WEAK
SO STORM BEHAVIOR IS EXPECTED TO BE MORE PULSE LIKE. TEMPS WILL
RANGE FROM THE MID 70S TO MID 80S...WITH COOLER TEMPS OVER NW SD/NE
WY WHERE THE FROPA OCCURS EARLIER THIS MORNING. WINDS IMMEDIATELY
BEHIND THE FRONTAL BOUNDARY WILL BECOME BREEZY...WITH GUSTS TO
AROUND 30KT...BUT WILL BE LIMITED TO AN HOUR OR TWO AFTER THE FRONT
PASSES.

WEAK RIDGING BUILDS BEHIND THE DEPARTING WAVE TONIGHT CLEARING OUT
PRECIP LATE TNGT TO SATURDAY MRNG. THE NEXT LONGWAVE TROUGH WILL
CROSS THE PACIFIC NW TO NRN ROCKIES SATURDAY...WITH ACTIVE SW FLOW
DEVELOPING. CHANCES FOR SHRA/TSRA WILL AGAIN RETURN SAT AFTN/EVNG.
GOOD INSTABILITY AND STRONG LL SHEAR OVER NW SD WILL RESULT IN
STRONG TO SEVERE TSRA SAT AFTN/EVNG. LARGE HAIL AND DAMAGING WINDS
ARE THE MAIN THREATS.

&&

.LONG TERM...SUNDAY THROUGH THURSDAY
ISSUED AT 251 AM MDT FRI AUG 29 2014

ACTIVE/PROGRESSIVE NORTHERN STREAM FLOW WILL CONTINUE THROUGH THE
PERIOD WITH A STRONG UPPER LEVEL TROUGH ON TRACK TO ADVECT THROUGH
THE REGION SUN...WITH A WEAKER SHORTWAVE IMPULSE LIKELY MONDAY.
TROUGH RELOADING OVER THE NE PAC TUE-WED FAVORED IN ECMWF/GFS/GEM
SOLUTIONS TUE...WHICH WILL SUPPORT SHORTWAVE RIDGING OVER THE
NORTHERN PLAINS WITH DRY AND WARMER CONDITIONS TUE-WED. NO SIG
CHANGES FROM THE PREVIOUS FORECAST GIVEN VERY GOOD DETERMINISTIC
MODEL CONSISTENCY AND CONTINUITY THROUGH THE PERIOD...WHICH IS IN
LINE WITH GEFS/NAEFS MEANS.

UPPER LEVEL TROUGH WILL BE IN THE PROCESS OF SHIFTING EAST ACROSS
THE NORTHERN PLAINS SUNDAY. ASSOCIATED MID LEVEL COLD POOL WILL
SUPPORT STEEP LL LAPSE RATES OVER THE FA WITH RESIDUAL LL MOISTURE
IN PLACE. DIURNAL HEATING COUPLED WITH BH/NE WY TERRAIN INFLUENCES
SHOULD SUPPORT SCT TO ISOLD SHRA/TS ESP SOUTH HALF OF THE FA.
REMAINED CLOSE TO PREVIOUS POP NUMBERS WITH MID RANGE CHANCE
COVERING PRECIP CONCERNS. OTHERWISE...A WEAKER WESTERLY FLOW IMPULSE
STILL INDICATED IN FORECAST MODELS MONDAY...POSSIBLY SUPPORTING A
FEW SHRA/TS...ALTHOUGH DRY PROFILES WILL LIMIT QPF AND
COVERAGE...ESP AWAY FROM THE BH. DRY CONDS EXPECTED TUE-WED WITH
MEAN DEEP LAYER RIDGING. THE NEXT NE PAC UPPER LEVEL TROUGH WILL
EJECT EAST INTO THE NORTHERN PLAINS WED NIGHT INTO
THUR...INTERACTING WITH A LEE SIDE TROUGH. INCREASING LSA WED NIGHT
THROUGH THUR WILL SUPPORT INCREASING CHANCES FOR SHRA/TS...FAR NW
SAT NIGHT WITH POPS TRENDING SOUTH THROUGH THUR AS THE UPPER TROUGH
SHIFTS EAST WITH THE REFLECTED SFC WAVE. DID BUMP POPS UP TO LOW
CHANCE NW 2/3 THUR NIGHT.

COOL/BELOW NORMAL TEMPS /5-10 DEGREES/ EXPECTED SUNDAY THROUGH
MONDAY...ESP NW AREAS. WARMING CONDITIONS CAN BE EXPECTED TUE-THUR
MOST AREAS. HOWEVER...NW AREAS MAY SEE THE START OF A COOLING TREND
THUR AS THE NEXT COLD FRONT SHIFTS SE INTO THE REGION.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z SATURDAY MORNING)
ISSUED AT 506 AM MDT FRI AUG 29 2014

MVFR CONDITIONS IN PATCHY FOG AND STRATUS WILL WANE OVER WESTERN
SOUTH DAKOTA THIS MORNING. A BAND OF ISOLATED TO SCATTERED SHOWERS
WILL MOVE EAST ACROSS NORTHEASTERN WYOMING AND INTO WESTERN SD
THIS MORNING AS AN UPPER LEVEL IMPULSE PUSHES EAST INTO THE
REGION. AN ISOLD MORNING TS IS ALSO POSSIBLE IN NE WY. THIS SAME
IMPULSE WILL SUPPORT ADDITIONAL CHANCES FOR SHRA/TS THIS AFTERNOON
WITH DIURNAL HEATING...MAINLY WESTERN AND CENTRAL SD. LOCAL MVFR
CONDS WILL BE POSSIBLE WITH ANY SHRA/TS THIS AFTERNOON.
OTHERWISE...VFR CONDITIONS WILL PREVAIL.

&&

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

$$

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





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