Area Forecast Discussion
Issued by NWS Rapid City, SD

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000
FXUS63 KUNR 231715
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
1115 AM MDT SAT AUG 23 2014

.UPDATE...
ISSUED AT 945 AM MDT SAT AUG 23 2014

MAIN SHORTWAVE AHEAD OF THE ID/WY UPPER LOW IS NOW CROSSING WRN
SD. SUBSIDENCE BEHIND THE WAVE HAS ENDED PRECIP ACROSS SW SD...THE
BLKHLS...MUCH OF NE WY...AND SCNTRL SD. NO FLOODING ISSUES HAVE
BEEN SEEN WITH AREA STREAMS...THUS HAVE CANCELLED THE FLOOD WATCH.
THE WATCH DOES REMAIN FOR NW SD AND PORTIONS OF NE WY WHERE
HEAVIER RAINFALL FELL LAST NIGHT. SHORT TERM MODELS SHOW
ADDITIONAL STORM DEVELOPMENT THIS AFTERNOON AND MIGRATING EASTWARD
TONIGHT. LARGE SCALE FLOODING IS NOT EXPECTED FROM THIS ADDITIONAL
PRECIP LATER TODAY. INSTABILITY WILL BE RELATIVELY WEAK ACROSS
MOST OF THE CWA...EXCEPT 1000 TO 2000 J/KG OVER SOUTH CENTRAL SD
LATER IN THE AFTN INTO THE EVNG. HRRR/NAM SUGGEST A LINE OF STORMS
PUSHING INTO SCNTRL SD THROUGH THIS TIME PERIOD. LL SHEAR IS
MARGINAL...BUT WITH INSTABILITY PRESENT...SOME OF THOSE STORMS
COULD END UP BEING STRONG OR EVEN SEVERE.

&&

.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 18Z TAFS THROUGH 18Z SUNDAY)
ISSUED AT 1111 AM MDT SAT AUG 23 2014

SCATTERED SHOWERS/THUNDERSTORMS WILL BE FOUND ACROSS THE AREA THIS
AFTERNOON AND EVENING...WITH BEST CHANCE ACROSS NORTHWEST SOUTH
DAKOTA. WIDESPREAD IFR VSBY WITH THE PRECIPITATION. MVFR/LCL IFR
CIGS WILL PERSIST ACROSS MUCH OF NORTHEAST WYOMING/WESTERN SOUTH
DAKOTA THROUGH TONIGHT.

&&

.HYDROLOGY...
ISSUED AT 945 AM MDT SAT AUG 23 2014

FLOOD WATCH CONTINUES ACROSS NORTHWEST SOUTH DAKOTA AS A POTENT
SHORTWAVE CONTINUES ACROSS THE WRN SD PLAINS. GIVEN THE VIGOROUS
UPPER LEVEL DYNAMICS AND THE AMPLE MOISTURE AND EASTERLY LOW LEVEL
FLOW...MODERATE TO HEAVY RAIN WILL CONTINUE THROUGH THE EARLY
AFTERNOON...THEN DECREASE IN THE LATE AFTERNOON HOURS.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...FLOOD WATCH UNTIL 6 PM MDT THIS EVENING FOR SDZ001-002-012>014-
     032-073.

WY...FLOOD WATCH UNTIL 6 PM MDT THIS EVENING FOR WYZ054-056-071.

&&

$$

UPDATE...13
SHORT TERM...MLS
LONG TERM...10
AVIATION...
HYDROLOGY...13






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