Area Forecast Discussion
Issued by NWS Rapid City, SD

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000
FXUS63 KUNR 201112
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
512 AM MDT SAT SEP 20 2014

.SHORT TERM...TODAY THROUGH SUNDAY NIGHT
ISSUED AT 158 AM MDT SAT SEP 20 2014

POTENT NORTHERN STREAM TROUGH AND ASSOCIATED LL COLD
FRONT WILL CONTINUE TO SHIFT SE ACROSS THE UPPER MIDWEST AND
NORTHERN PLAINS TODAY. SFC HIGH PRESSURE WILL BUILD INTO THE REGION
TODAY WITH DRY WEATHER EXPECTED THROUGH THE PERIOD...SAVE FOR SOME
EXITING MORNING SHRA OVER SCENTRAL SD. STRONG LL MOMENTUM FIELDS
ASSOCIATED WITH THE DEPARTING UPPER TROUGH WITH DIURNAL
MIXING/PRESSURE RISES/AND CAA WILL SUPPORT WINDY CONDITIONS NW SD
TODAY...THE MAIN FOCUS IN THE PERIOD. WESTERN NOAM RIDGE WILL AGAIN
SHIFT EAST SUNDAY...WITH WARMING CONDITIONS. MID LEVEL MOISTURE PLUME
ASSOCIATED WITH THE SW CONUS CLOSED UPPER TROUGH WILL BEGIN TO PUSH
INTO THE REGION SUNDAY NIGHT...POSSIBLY SUPPORTING A SHRA/TS LATE
SUNDAY NIGHT FAR SW.

TODAY/TONIGHT...LINGERING PRE-DAWN SHRA/TS OVER THE SOUTHERN HALF OF
THE FA WILL WANE AS THE LL THETA-E RIDGE SHIFTS SOUTH AND JET
STREAK FORCING WANES. DRY CONDITIONS WILL PREVAIL THE REMAINDER OF THE
DAY WITH WINDY CONDITIONS DEVELOPING OVER THE NW SD PLAINS. STRONG
ISOLATION WILL SUPPORT DOWNWARD MOMENTUM TRANSFER OF STRONG LL FLOW
GIVEN STEEP LL LAPSE RATES/CAA REGIME/AND SFC PRESSURE RISES. BUFR
DATA SUGGEST FREQUENT GUSTS OVER 35 KNOTS NW SD WITH SUSTAINED WINDS
AT TIMES OF 25 TO 30 KNOTS. HAVE ADJUSTED WINDS UP THERE...AND WILL
ISSUE A WIND ADV. GIVEN THERMAL FIELDS...HAVE LOWERED TEMPS A FEW
DEGREES...ESP NW SD AND NE WY. COOL CONDITIONS EXPECTED TONIGHT WITH
CLEAR SKIES/LIGHT WINDS/AND DRY AIR IN PLACE.

SUNDAY...SFC RIDGE WILL SHIFT SE OF THE REGION SUPPORTING INCREASING
SOUTHERLY FLOW OVER THE WESTERN HALF. WAA WILL BE ONGOING WITH
SLIGHTLY WARMER DAYTIME HIGHS. SW CONUS UPPER TROUGH WILL EJECT
TOWARD THE REGION UNDER THE WESTERN NOAM RIDGE...WITH MID AND UPPER
LEVEL SW FLOW INCREASING MOISTURE INTO THE REGION. LEADING EDGE OF
HIGH THETA-E AIR /INDICATED WELL AT H7/ WILL ENTER THE SW FA LATE
SUNDAY NIGHT...SUPPORTING AN INCREASE IN CLOUDS WITH THE POTENTIAL
FOR SHRA/TS FAR SW. LACK OF STRONG FORCING WITH OVERNIGHT TIMING
SUPPORT A CONTINUED LOW POP ATTM.

&&

.LONG TERM...MONDAY THROUGH FRIDAY
ISSUED AT 158 AM MDT SAT SEP 20 2014

MODELS ARE STILL IN AGREEMENT ABOUT A CUT-OFF LOW
CROSSING THE REGION THROUGH FIRST HALF OF NEXT WEEK. RETURN FLOW
WILL SET UP WITH MOISTURE ADVECTING IN THE DEEP SOUTHERLY FLOW. THIS
COMBINED WITH SOME MINIMAL INSTABILITY WILL ALLOW FOR SHOWERS AND
THUNDERSTORMS MONDAY AND TUESDAY. DRIER AIR WILL RETURN WEDNESDAY AS
A RIDGE BUILDS...HOWEVER INSTEAD OF THE LOW PHASING BACK INTO THE
MAIN FLOW LIKE THE ECMWF...THE GFS KEEPS THE LOW IN THE NORTHERN
PLAINS AND HAS IT RETROGRESSING LATE IN THE WEEK. WILL HAVE TO SEE
IF THIS FEATURE REMAINS IN LATER RUNS. UPPER RIDGING WILL BUILD WITH
STRONG SUBSIDENCE CLEARING OUT SKIES THROUGH THE END OF THE WORK
WEEK. HIGHS WILL BE NEAR TO SLIGHTLY ABOVE AVERAGE FOR THE SECOND
HALF OF THE WEEK. MODELS ARE HINTING AT A LARGE UPPER TROUGH OVER
THE WESTERN CONUS FOR NEXT WEEKEND...POSSIBLY BRINGING MORE WET
WEATHER TO THE REGION.

&&

.AVIATION...FOR THE 12Z TAFS THROUGH 12Z SUNDAY MORNING
ISSUED AT 511 AM MDT SAT SEP 20 2014

STRONG N/NW WINDS ARE EXPECTED ACROSS NORTHWESTERN SOUTH
DAKOTA TODAY...DIMINISHING IN THE LATE AFTERNOON AND EVENING. VFR
CONDITIONS WILL PREVAIL THROUGH SUNDAY MORNING.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...WIND ADVISORY FROM 9 AM THIS MORNING TO 5 PM MDT THIS AFTERNOON
     FOR SDZ001-002-012-013-025-026-031-072-073.

WY...NONE.
&&

$$

SHORT TERM...JC
LONG TERM...POJORLIE
AVIATION...POJORLIE





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