Area Forecast Discussion
Issued by NWS Rapid City, SD

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000
FXUS63 KUNR 222337
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
537 PM MDT FRI AUG 22 2014

.SHORT TERM...THIS EVENING THROUGH SATURDAY NIGHT
ISSUED AT 251 PM MDT FRI AUG 22 2014

WATER VAPOR IMAGERY SHOWS A DEEP TROUGH/UPPER LOW OVER THE PACIFIC
NW WITH A STRONG SHORTWAVE EJECTING ACROSS THE DESERT SW. THIS
SHORTWAVE IS SHOWING A WELL DEFINED BAROCLINIC LEAD AS IT MOVES INTO
CO. SURFACE TROUGH OVER WY TO WRN KS WILL STRENGTHEN TONIGHT AS THE
WAVE SWINGS THRU THE CNTRL PLAINS INTO THE DAKOTAS. THIS SYSTEM WILL
BRING WIDESPREAD PRECIP TO MUCH OF WRN SD THROUGH THE NIGHT INTO SAT
MORNING.

SHOWERS AND STORMS WILL INCREASE ACROSS THE CWA THIS AFTERNOON INTO
THE EVENING. MLCAPE OVER THE AREA GENERALLY IN TO 500 TO 1500 J/KG
RANGE...WITH THE HIGHER RANGE OVER THE WRN SD PLAINS. SHEAR VALUES
ARE STRONG ENOUGH FOR A COUPLE STORMS TO BE STRONG TO SEVERE...BUT
WIDESPREAD SEVERE STORMS ARE NOT EXPECTED. BIGGER CONCERN TONIGHT
WILL BE HEAVY RAIN POTENTIAL. MODELS SHOWING HIGHER THAN AVERAGE
PWATS OVER THE REGION. BASED ON THE LAST COUPLE OF HEAVY PRECIP
EVENTS AND THE 12Z KRAP SOUNDING...THE NAM SEEMS TO BE
OVERESTIMATING PRECIPITABLE WATER WITH IT SHOWING 180-220 PERCENT OF
NORMAL TONIGHT AND TOMORROW. THE GFS SEEMS MORE REASONABLE AT
120-150 PERCENT OF NORMAL. AS THE SHORTWAVE APPROACHES
TONIGHT...PRECIP WILL BECOME MORE WIDESPREAD TOWARD 06Z PUSHING
NORTHWARD MAINLY OVER THE WRN SD PLAINS INTO THE BLACK HILLS AREA.
THOUGH MODEL IS STILL LACKING CONSISTENCY...THERE IS AGREEMENT THAT
THE BULK OF PRECIP WITHIN THE CWA WILL BE ACROSS WRN SD. THE PRECIP
WILL BE MORE OF THE LESS INTENSE AND MORE WIDESPREAD TYPE...NOT
NECESSARILY MORE INTENSE THUNDERSTORM PRECIP. AND WITH DRY
CONDITIONS OVER MOST OF THE WRN SD PLAINS...DONT THINK ANY FLASH
FLOOD/LONG DURATION FLOOD HEADLINES WILL BE NEEDED. SOME CREEKS THE
GET LOCALLY HEAVY RAINFALL COULD SEE CREEKS AND STREAMS RUNNING
HIGH.

LOW PRESSURE SYSTEM WILL BECOME STACKED LATE SATURDAY OVER MT/ND
WITH DRY AIR INTRUDING ACROSS THE CWA. MOST OF THE PRECIP WILL END
ACROSS THE AREA SAT AFTN/EVNG AND DRY AIR WORKS IN FROM THE W/SW.
COLDER AIR WILL ADVECT IN SAT NIGHT BRINGING BELOW AVERAGE TEMPS
INTO THE EXTENDED.

&&

.LONG TERM...SUNDAY THROUGH FRIDAY
ISSUED AT 251 PM MDT FRI AUG 22 2014

A TRANSITIONAL PATTERN WILL CONTINUE THROUGH THE EXTENDED PERIOD. ON
12Z SUNDAY THE LARGE UPPER LOW FROM THIS WEEKEND WILL BE OVER SERN
MT...AND THEN SLOWLY MOVE NORTHEAST TO NCNTRL ND BY 00Z MONDAY AND
SRN MANITOBA BY 12Z MONDAY. AT THE SAME TIME A BROAD TROUGH WILL
PERSIST OVER THE ROCKIES...WITH SHORT-WAVE RIDGING OVER THE CWA. A
DRY SLOT WILL MOVE ACROSS THE CWA ON SUNDAY...KEEPING MOST OF THE
PRECIP NORTH OF THE AREA. THIS WILL LEAD TO A SHORT PERIOD OF
GENERALLY DRY WEATHER.

BY 12Z MONDAY THE WRN US TROUGH WILL BEGIN TO EJECT TWO SHORT-WAVE
TROUGHS ACROSS THE CWA. GIVEN THE RESIDUAL MOISTURE AND INSTABILITY
THERE SHOULD BE SCT SHRA/TSRA DURING THIS PERIOD. ON TUESDAY...THE
ROCKIES TROUGH WILL MOVE EAST INTO THE CNTRL US (BY 12Z WED). THIS
WILL MAINTAIN A CHANCE OF SHRA/TSRA...WITH DRYING TOWARD 12Z WED.
TEMPERATURES ALSO WILL BE 5-10 DEGREES FAHRENHEIT BELOW AVERAGE
SUNDAY THROUGH TUESDAY.

ON WEDNESDAY THE TROUGH WILL MOVE EAST AND A LARGE-SCALE RIDGE WILL
MOVE OVER THE CNTRL/ERN ROCKIES. THIS WILL PERSIST INTO THURSDAY AND
MOVE OVER THE CWA...BUT WITH A GENERAL FLATTENING. THERE IS SOME
SIGNAL THAT ONE OR TWO SHORT-WAVE TROUGHS WILL TOP THE RIDGE ACROSS
THE NRN CONUS. IF THIS COMES TO PASS THERE WOULD BE ISOLD SHRA/TSRA
ACROSS AT LEAST THE NRN CWA. QUASI-ZONAL FLOW WITH ADDITIONAL SHORT-
WAVE TROUGHS IS POSSIBLE THROUGH FRIDAY...THUS DO NOT EXPECT THE
WEATHER TO BE COMPLETELY DRY. NEVERTHELESS...WEDNESDAY THROUGH
FRIDAY SHOULD SEE A WARMING AND DRYING TREND.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z SATURDAY EVENING)
ISSUED AT 536 PM MDT FRI AUG 22 2014

WEATHER WILL DETERIORATE THROUGH TONIGHT AS LOW PRESSURE BRINGS A
LARGE AREA OF SHRA/TSRA ACROSS MUCH OF THE FORECAST AREA. MVFR/IFR
CIGS WILL BE COMMON WITH THE PRECIP...AND BY LATE TNGT WIDESPREAD
MVFR/IFR CIGS/VSBYS WITH STRATUS AND SOME FOG WILL OCCUR ACROSS
MUCH OF WRN/CNTRL SD...PERSISTING THROUGH MOST OF SATURDAY MRNG.

&&

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

$$

SHORT TERM...13
LONG TERM...BUNKERS
AVIATION...HELGESON




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