Area Forecast Discussion
Issued by NWS Rapid City, SD

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000
FXUS63 KUNR 170329
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
929 PM MDT SAT AUG 16 2014

.SHORT TERM...THIS EVENING THROUGH SUNDAY NIGHT
ISSUED AT 228 PM MDT SAT AUG 16 2014

AN ACTIVE SHORT WAVE IS MOVING ACROSS THE EASTERN DAKOTAS THIS
AFTERNOON LEAVING THE HIGH PLAINS AND BLACK HILLS REGION IN AN
AREA WITH GENERAL SUBSIDENCE AND LOW HUMIDITY. THE HIGH PRESSURE
RIDGE OVER THE WESTERN U.S. IS BEING FLATTENED BY A MODERATELY
STRONG UPPER LEVEL SYSTEM MOVING SLOWLY EASTWARD ALONG THE
CANADIAN/MONTANA BORDER. THIS SYSTEM IS NOT PRODUCING MUCH
WEATHER...DUE TO LOW RELATIVE HUMIDITIES. THE LATE SUMMER MONSOON
PLUME HAS BEEN PUSHED OFF TO THE SOUTHEAST BY THE SOUTHWESTERN
U.S. UPPER RIDGE AND WEST TO NORTHWEST FLOW ALOFT OFF THE CONTDVD.

TONIGHT...THE APPROACHING SHORT WAVE IS EXPECTED TO SLOWLY INCREASE
INSTABILITY...MOSTLY OVER NORTHWESTERN SOUTH DAKOTA AND POSSIBLY
SOME OF THE HIGHER TERRAIN IN NORTHEAST WYOMING LATE THIS EVENING.
ISOLATED SHOWERS ARE POSSIBLE BUT MOSTLY OF THE HIGH BASED GUSTY
WIND VARIETY DUE TO THE RELATIVELY DRY LOW LEVELS.

SUNDAY AND SUNDAY NIGHT...THE BORDER SHORT WAVE WILL BRING IN A
LITTLE COOLER AIR ALOFT...HELP DESTABILIZE THE ATMOSPHERE AND
PROVIDE A FEW WEAK IMPULSES DURING THE DAY...TRIGGERING A FEW STORMS
OVER THE HIGHER TERRAIN OF NORTHEAST WYOMING THE BLKHLS AND
NORTHWEST SOUTH DAKOTA BY MIDDAY. THE SYSTEM IS THEN FORECAST TO
BECOME BETTER ORGANIZED INTO AN MCS TYPE STRUCTURE...OR AT LEAST
LARGER CLUSTERS...AS IT MOVES INTO THE CENTRAL DAKOTAS LATE IN THE
DAY. THE MONSOON PLUME NEVER REALLY BECOMES A FACTOR OVER WESTERN
SOUTH DAKOTA OR WYOMING SO PW REMAINS MODERATE. CELL MOVEMENTS
SHOULD STAY ABOVE 10 KNOTS WITH THE INCREASE FLOW ASSOCIATED WITH
THE SHORT WAVE.  SO THE POTENTIAL FOR HEAVY PRECIPITATION IN THIS
FORECAST AREA IS LOW FOR THIS EVENT.

&&

.LONG TERM...MONDAY THROUGH SATURDAY
ISSUED AT 228 PM MDT SAT AUG 16 2014

THE MID-LONG RANGE FORECAST MODELS SHOW AN UPPER TROUGH PERSISTING
OVER THE WEST COAST THROUGH MUCH OF THE EXTENDED FORECAST PERIOD.
THE RESULT WILL BE ACTIVE SOUTHWESTERLY FLOW ALOFT OVER THE FORECAST
AREA AND THE POSSIBILITY OF ISOLD-SCT THUNDERSTORMS OVER PARTS OF
THE AREA NEARLY EVERY DAY. THE MODELS BEGIN TO DIVERGE HEADING INTO
THE WEEKEND WITH THE ECMWF PROGRESSING THE UPPER TROUGH ACROSS THE
NORTHERN PLAINS WHILE THE GFS KEEPS REGENERATING THE UPPER LOW OVER
THE PACIFIC NORTHWEST. EITHER WAY...CONDITIONS WILL LIKELY REMAIN
UNSETTLED. HOWEVER...THE TEMPERATURE FORECAST WILL BE DEPENDENT ON
THE EVENTUAL PROGRESS OF THE TROUGH...COOLER WITH THE GFS SOLUTION
AND WARMER WITH THE ECMWF.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SUNDAY NIGHT)
ISSUED AT 928 PM MDT SAT AUG 16 2014

MOSTLY VFR CONDITIONS ARE EXPECTED THROUGH THE PERIOD...HOWEVER
SCT MVFR/IFR CIGS ARE POSSIBLE OVERNIGHT OVER PARTS OF NWRN-CNTRL
SD WHERE MOIST NORTHEAST FLOW SHOULD PRODUCE STRATUS. OTHERWISE...
ISOLD SHRA/TSRA ARE EXPECTED OVERNIGHT ACROSS NWRN-WCNTRL SD...AND
THERE WILL BE SCT SHRA/TSRA OVER THE BLKHLS AND WRN SD SUNDAY
AFTN...WHICH MAY PRODUCE LCL MVFR CIGS/VSBYS...AS WELL AS LARGE
HAIL AND STRONG WIND GUSTS.

&&

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

&&

$$

SHORT TERM...CARPENTER
LONG TERM...10
AVIATION...BUNKERS



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