Area Forecast Discussion
Issued by NWS Rapid City, SD

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000
FXUS63 KUNR 292111
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
311 PM MDT MON SEP 29 2014

.SHORT TERM...THIS EVENING THROUGH TUESDAY NIGHT
ISSUED AT 240 PM MDT MON SEP 29 2014

LATEST SFC ANALYSIS SHOWS A LEE SIDE TROUGH DEEPENING AS AN UPPER
LOW...CURRENTLY OVER IDAHO/WRN WYOMING MOVES EASTWARD. EASTERLY
UPSLOPE COMPONENT TO THE SFC WINDS IS KEEPING LOW CLOUDS AND AREAS
OF FOG OVER MUCH OF WESTERN SOUTH DAKOTA THIS AFTERNOON. THE
INITIAL BAND OF RAIN AND THUNDERSTORMS CONTINUES TO MOVE SLOWLY
EASTWARD TOWARD CENTRAL SOUTH DAKOTA WHERE SOME STRONGER
THUNDERSTORMS ARE POSSIBLE DURING THE LATE AFTERNOON/EARLY EVENING.

TONIGHT THROUGH TUESDAY AFTERNOON...THE UPPER LOW WILL CONTINUE TO
SPIN EASTWARD...BECOMING TIGHTLY WRAPPED OVER THE CWA BY 12Z
TUESDAY...THEN MOVING QUICKLY TO THE NORTHEAST TUESDAY EVE. FORCING
AHEAD OF THE UPPER LOW WILL BE RELATIVELY STRONG WITH A SUSTAINED
PERIOD OF UPPER LEVEL DIVERGENCE. THE LOW LEVEL FLOW OF MOISTURE
WILL BECOME INCREASINGLY STRONG AS THE SURFACE LOW OVER EASTERN CO
DEEPENS AND HEADS NORTH TONIGHT. SUSTAINED 850-700MB THETA-E
ADVECTION...AS WELL AS STRONG ISENTROPIC LIFT WILL GENERATE WAVES
OF SHRA/TSRA OVER THE AREA TONIGHT INTO TUESDAY. THE HEAVIEST RAIN
IS EXPECTED TO FALL TONIGHT/EARLY TUESDAY WHEN DEEP LAYER LIFT IF
AT A MAXIMUM. 1 TO 2.5 ADDITIONAL INCHES OF RAIN ARE EXPECTED TO
FALL...ESP OVER PARTS OF NORTHEASTERN WYOMING AND WESTERN SOUTH
DAKOTA. DUE TO THE SOAKING RAIN THAT FELL OVERNIGHT AND THIS
MORNING...ESP OVER SOUTHWESTERN SOUTH DAKOTA AND THE BLACK HILLS
AREA...COMBINED WITH THE EXPECTED ADDITIONAL RAINFALL TONIGHT AND
TUESDAY...HAVE ISSUED A FLOOD WATCH FOR NORTHEASTERN WYOMING AND
WESTERN SOUTH DAKOTA WHERE FLOODING OF SMALL CREEKS AND STREAMS
WILL BE POSSIBLE.

TUESDAY NIGHT...THE SYSTEM QUICKLY MOVES AWAY BUT IT WILL LEAVE
CYCLONIC FLOW/MOISTURE IN IT/S WAKE. LEFTOVER -SHRA EXPECTED.

&&

.LONG TERM...WEDNESDAY THROUGH MONDAY
ISSUED AT 240 PM MDT MON SEP 29 2014

CYCLONIC FLOW WILL CONTINUE OVER THE REGION WEDNESDAY
WITH SOME SHOWERS POSSIBLE AS A SECONDARY UPPER WAVE ROUNDS THE BASE
OF THE BROAD TROUGH. A COOLER AIR MASS WILL ADVECT IN AS THE BACKSIDE
OF THE TROUGH PUSHES INTO THE UPPER MIDWEST. BREEZY NORTHWEST WINDS
ARE EXPECTED WEDNESDAY AS THE PRESSURE GRADIENT TIGHTENS BETWEEN THE
EXITING LOW AND THE INCOMING HIGH...AND AGAIN ON THURSDAY AS A
120-KT UPPER LEVEL JET MOVES OVER THE AREA. THE ECM IS HINTING AT A
FEW SHOWERS ACROSS THE WESTERN CWA THURSDAY AS ANOTHER WAVE SWEEPS
THROUGH THE REGION...ALTHOUGH THE GFS IS DRY. UPPER RIDGING WILL
BUILD ACROSS THE WESTERN CONUS FOR THE LATTER PART OF THE
WEEK...WITH NORTHWEST FLOW REMAINING OVER THE NORTHERN PLAINS INTO
NEXT WEEK. THIS WILL KEEP DRIER WEATHER ACROSS THE AREA ALONG WITH
TEMPERATURES NEAR TO BELOW SEASONAL AVERAGES.

&&

.AVIATION...FOR THE 18Z TAFS THROUGH 18Z TUESDAY
ISSUED AT 240 PM MDT MON SEP 29 2014

MVFR/IFR CONDITIONS WILL CONTINUE THROUGH TONIGHT AND
INTO TUESDAY MORNING AS A STRONG STORM SYSTEM SLOWLY CROSSES THE
REGION. THIS SYSTEM WILL CONTINUE TO BRING WIDESPREAD
SHOWERS/ISOLATED STORMS TO THE AREA. IFR VSBY IS EXPECTED WITH THE
HEAVIER PRECIP.

&&

.HYDROLOGY...
ISSUED AT 240 PM MDT MON SEP 29 2014

A LARGE LOW PRESSURE SYSTEM WILL BRING WIDESPREAD RAIN TO PARTS
OF NORTHEASTERN WYOMING AND WESTERN SOUTH DAKOTA TONIGHT THROUGH TUESDAY
MORNING. THERE MAY BE A BREAK IN THE RAIN OVER SOME AREAS INTO THE
EARLY EVENING HOURS...BUT WIDESPREAD RAIN IS EXPECTED TO REDEVELOP
THIS EVENING...AND CONTINUE THROUGH TUESDAY MORNING.

SOME AREAS OF THE BLACK HILLS AND FAR SOUTHWESTERN SOUTH DAKOTA
HAVE ALREADY RECEIVED 1 TO 2 INCHES OF RAIN. ANOTHER 1 TO 2
INCHES OF RAIN...WITH LOCAL AMOUNTS AS HIGH AS 3 INCHES ARE
POSSIBLE OVER PARTS OF NORTHEASTERN WYOMING AND WESTERN SOUTH
DAKOTA TONIGHT THROUGH TUESDAY MORNING. THE EXCESSIVE RAINFALL MAY
CAUSE FLOODING OF SMALL CREEKS AND STREAMS. THE RAIN WILL TAPER
OFF FROM SOUTH TO NORTH LATER ON TUESDAY.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...FLOOD WATCH THROUGH TUESDAY MORNING FOR SDZ001-002-012-013-
     024>031-041-042-072>074.

WY...FLOOD WATCH THROUGH TUESDAY MORNING FOR WYZ056-057-071.

&&

$$

SHORT TERM...10
LONG TERM...POJORLIE
AVIATION...POJORLIE
HYDROLOGY...10





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