Area Forecast Discussion
Issued by NWS Rapid City, SD

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000
FXUS63 KUNR 230918
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
318 AM MDT SAT AUG 23 2014

.SHORT TERM...TODAY THROUGH SUNDAY NIGHT
ISSUED AT 318 AM MDT SAT AUG 23 2014

09Z SURFACE ANALYSIS HAD FRONTAL BOUNDARY EXTENDING ACROSS THE CWA
FROM SOUTHEASTERN WYOMING INTO NORTH CENTRAL SOUTH DAKOTA. LATEST
WATER VAPOR IMAGERY SHOWS A DIGGING TROF ACROSS THE PACIFIC
NORTHWEST AS A POTENT SHORTWAVE MOVES NORTHEASTWARD FROM COLORADO.
RADAR IMAGERY IS SHOWING WIDESPREAD PRECIPITATION ACROSS THE
FORECAST AREA. LATEST BLENDED TOTAL PRECIPITABLE WATER PRODUCTS
INDICATE 1.0 - 1.5 INCHES. THESE PW AMOUNTS COMBINED WITH
EAST-SOUTHEASTERLY FLOW WILL CONTINUE TO ALLOW RAIN TO FILL
IN THROUGH THE MORNING HOURS. CURRENT FORECAST PRECIPITATION AMOUNTS
OF 1-2 INCHES STILL SEEM TO BE ON TRACK WITH SOME LOCALLY HIGHER
AMOUNTS POSSIBLE.

OVERALL MODEL PWS HAVE TRENDED BACK FROM PREVIOUS RUNS WITH AVERAGE
PWS OF 120 TO 150 PERCENT OF NORMAL. THIS SEEMS REASONABLE...THUS
EXPECT THE HEAVIEST RAINFALL TO CONTINUE THROUGH THIS AFTERNOON.

TEMPERATURES AHEAD OF THE FRONTAL BOUNDARY THIS AFTERNOON WILL REACH
INTO THE 80S. FORECAST SHEAR PROFILES AND INSTABILITY IN SOUTH
CENTRAL SOUTH DAKOTA COULD SUPPORT SUPERCELLS. WITH THE MOIST AIRMASS
IN PLACE WILL HAVE TO MONITOR CONDITIONS FOR THE POSSIBILITY OF HP
SUPERCELLS PRODUCING LARGE HAIL AND STRONG WINDS.

THE SYSTEM WILL BECOME STACKED LATE TONIGHT OVER MT/ND WITH DRY AIR
INTRUDING ACROSS THE CWA. MOST OF THE RAIN WILL END ACROSS THE
AREA TONIGHT INTO SUNDAY MORNING AS DRY AIR WORKS IN FROM THE
WEST-SOUTHWEST. COLDER AIR WILL ADVECT IN TONIGHT BRINGING BELOW
AVERAGE TEMPERATURES ON SUNDAY.

&&

.LONG TERM...MONDAY THROUGH FRIDAY
ISSUED AT 318 AM MDT SAT AUG 23 2014


ON MONDAY MORNING THE WRN CONUS TROUGH WILL BEGIN TO MOVE EASTWARD
TOWARD THE FORECAST AREA. GIVEN THE RESIDUAL MOISTURE AND
INSTABILITY THERE WILL BE A CHANCE OF SHOWERS AND THUNDERSTORMS FROM
MONDAY INTO WEDNESDAY MORNING. TEMPERATURES 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. ZONAL FLOW WITH ADDITIONAL SHORTWAVE
TROUGHS WILL BE 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 12Z TAFS THROUGH 12Z SUNDAY MORNING
ISSUED AT 318 AM MDT SAT AUG 23 2014


A STRONG LOW PRESSURE SYSTEM WILL BRING WIDESPREAD SHRA/TSRA TO THE
FORECAST AREA THIS MORNING WITH THE AREA OF PRECIP MOVING NORTH IN
THE AFTERNOON. WIDESPREAD MVFR/IFR CIGS/VSBYS WITH STRATUS AND SOME
FOG WILL OCCUR WITH THE PRECIPITATION ACROSS MUCH OF NERN WY AND WRN
AND CNTRL SD...PERSISTING THROUGH MOST OF THIS MORNING. CONDITIONS
WILL BEGIN TO IMPROVE FROM SOUTH TO NORTH LATE THIS
MORNING...ALTHOUGH MVFR CIGS ARE EXPECTED TO PERSIST OVER PARTS OF
NERN WYOMING AND NWRN SOUTH DAKOTA THROUGH THE AFTERNOON AND
OVERNIGHT.

&&

.HYDROLOGY...
ISSUED AT 318 AM MDT SAT AUG 23 2014

FLOOD WATCH CONTINUES ACROSS THE ENTIRE AREA AS A POTENT
SHORTWAVE TRACKS THROUGH THE REGION. GIVEN THE VIGOROUS UPPER LEVEL
DYNAMICS AND THE AMPLE MOISTURE AND EASTERLY LOW LEVEL
FLOW...EXPECT A LONG DURATION EVENT WITH MODERATE TO HEAVY RAIN
THROUGH THE AFTERNOON HOURS.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...FLOOD WATCH THROUGH THIS AFTERNOON FOR SDZ001-002-012>014-
     024>032-041>044-046-047-049-072>074.

WY...FLOOD WATCH THROUGH THIS AFTERNOON FOR WYZ054>058-071.

&&

$$

SHORT TERM...MLS
LONG TERM...10
AVIATION...10
HYDROLOGY...MLS





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