Area Forecast Discussion
Issued by NWS Rapid City, SD

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000
FXUS63 KUNR 230407
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
907 PM MST SAT NOV 22 2014

.UPDATE...
ISSUED AT 903 PM MST SAT NOV 22 2014

04Z SURFACE ANALYSIS HAD LOW NEAR CYQR WITH COLD FRONT TO KRAP TO
SOUTH CENTRAL WY. COUPLE OF HOURS OF GUSTY WINDS ASSOCIATED WITH
COLD FRONT AS WELL AS SOME -SHRASN. 00Z KUNR SOUNDING SHOWS LIFT
AHEAD OF SHORTWAVE OVER SOUTHEAST MT BEING WASTED ON SATURATION
EARLIER THIS EVENING. LATEST RADAR/OBSERVATIONS DO SUGGEST LOWER
TROPOSPHERE MOISTENING ENOUGH FOR PRECIPITATION TO REACH THE
GROUND...ESPECIALLY OVER NORTHWEST SD SO HAVE RAISED POPS THERE.

00Z GUIDANCE STILL SHOWS VERY WINDY DAY FOR MUCH OF THE AREA
SUNDAY. BUFKIT MOMENTUM TRANSFER INDICATES HIGH WIND WARNING
CRITERIA WINDS FROM K2WX TO KRAP DURING PEAK MIXING LATER SUNDAY
MORNING THROUGH LATE SUNDAY AFTERNOON...IN CONTRAST TO LESSER MOS
GUIDANCE WINDS. 40-50KT 850MB WINDS NOTED WITH SLIGHTLY HIGHER
VALUES HIGHER UP. STRONG SUBSIDENCE NOTED BEHIND TONIGHT/S
SHORTWAVE ALONG WITH WEAK COLD AIR ADVECTION DURING PEAK HEATING.
WILL CONVERT WATCH TO WARNING AND EXPAND ALONG THE FOOTHILLS A BIT
WITH UPDATE.

&&

.SHORT TERM...THIS EVENING THROUGH SUNDAY NIGHT
ISSUED AT 426 PM MST SAT NOV 22 2014

DEEPENING NW CONUS UPPER TROUGH WILL ADVECT THROUGH THE REGION
THROUGH SUNDAY...SUPPORTING A COLD FRONT INTO THE AREA...WITH
CHANCES FOR SNOW AND INCREASING WINDS. THERMAL RIDGE HAS SUPPORTED
A MILD DAY ACROSS THE AREA...ESP WHERE ENHANCED LOCAL MIXING HAS
OCCURRED. HOWEVER...INCREASING LSA WITH A LL COLD FRONT WILL
SUPPORT A WEAK FGEN BAND OF PRECIP ACROSS THE AREA TONIGHT.
SECONDARY COLD FRONT WITH STEEP LL LAPSE RATES AND CYCLONIC FLOW
ALOFT WILL THEN SUPPORT INCREASING CHANCES FOR DIURNALLY DRIVEN
SNOW SHOWERS SUNDAY...WITH FAVORABLE UPSLOPE FORCING OVER THE
NORTHERN HILLS. ACTIVE NW FLOW WILL SUSTAIN THROUGH SUNDAY
NIGHT...WITH ANOTHER IMPULSE EXPECTED TO INFLUENCE THE WESTERN FA
LATE SUNDAY.

TONIGHT...SPLITTING NW CONUS UPPER TROUGH WILL SUPPORT A WEAK HIGH
CENTERED FGEN RESPONSE OVER THE REGION WITH INCREASING MID LEVEL
MOISTURE. STEEP MID LEVEL LAPSE RATES COMBINED WITH SUFFICIENT MID
LEVEL MOISTURE AND INCREASING UVM SHOULD BE ENOUGH TO SUPPORT SCT
RAIN/SNOW SHOWERS OVER THE REGION...ESP NE WY WHERE BETTER FORCING
FOR ACCENT WILL BE IN PLACE. ANY PRECIP WILL MAINLY BE IN THE FORM OF
RAIN THIS EVENING...QUICKLY TRANSITIONING TO SNOW OVERNIGHT GIVEN
COOLING THERMAL FIELDS. ANY SNOW AMOUNTS WILL GENERALLY BE LESS THAN
ONE INCH. LL FLOW WILL VEER NW TONIGHT AND INCREASE AFTER MIDNIGHT.
INITIAL CAA PUSH AND PRESSURE RISES MAY SUPPORT A PERIOD OF NEAR ADV
WINDS AROUND KRAP AFTER MIDNIGHT. HOWEVER...WINDS SHOULD GENERALLY
REMAIN TAME UNTIL LATER SUNDAY MORNING.

SUNDAY...SECONDARY CAA PUSH AND INCREASING LL FLOW WILL SUPPORT A
WINDY DAY ACROSS THE REGION. MEAN BL FLOW PROGS SUPPORT SUSTAINED
WINDS OF 30-35 KNOTS ESP ACROSS FAR NW SD. BUFR PROGS INDICATE THE
POTENTIAL FOR WINDS OF 50 KNOTS TO MIX DOWN...ESP WITH THE SECONDARY
PRESSURE RISE SURGE EARLY SUNDAY AFTERNOON ACROSS THE FAR NW. IN
ADDITION...COLD POCKET ALOFT COMBINED WITH DIURNAL HEATING WILL
SUPPORT THE DEVELOPMENT OF SNOW SHOWERS...WITH LOCAL ENHANCED
DOWNWARD MOMENTUM TRANSPORT POSSIBLE IN THE VICINITY OF ANY SHOWER.
HAVE DECIDED TO ISSUE A WIND ADV FOR MUCH OF THE SD
PLAINS...RETAINING A HIGH WIND WATCH ACROSS THE FAR NW WHERE THE
BEST POTENTIAL FOR DOWNWARD MOMENTUM TRANSPORT OF 50 KNOT FLOW WILL
RESIDE. MEAN MODEL TRENDS HAVE SUPPORTED SLIGHTLY WEAKER WINDS
ACROSS THE AREA...BUT WOULD LIKE TO HAVE ANOTHER FORECAST RUN OR TWO
TO SEE IF THIS TREND SUSTAINS. THERE IS ALSO THE POTENTIAL FOR
LOCALIZED STRONG WINDS ALONG THE PLAINS OF THE EASTERN BLACK
HILLS...INCLUDING RAPID CITY...WITH NEAR HIGH WIND WARNING POSSIBLE.
HOWEVER...GIVEN THE LOW POTENTIAL/SHORT DURATION/AND LOCALIZED
NATURE...FEEL A WIND ADV IS MORE PRUDENT. THE OTHER HIGHLIGHT WILL
BE INCREASINGLY FAVORABLE CONDITIONS FOR UPSLOPE SNOWS ACROSS THE
NORTHERN BLACK HILLS...MAINLY FROM THE BEAR LODGE MOUNTAINS TO
CHEYENNE CROSSING. INCREASING FROUDE/MOISTURE/AND FLOW WITH COOLING
THERMAL FIELDS IN STEEP LL LAPSE RATES WILL SUPPORT A DECENT PERIOD
OF UPSLOPE FORCING...EXTENDING INTO THE DGZ. 1 TO 3 INCHES WITH
LOCALLY HIGHER AMOUNTS WILL BE POSSIBLE IN THIS AREA. SNOW WILL WIND
DOWN SUNDAY EVENING AS THE BL DRIES. HOWEVER...AS SECONDARY IMPULSE
WILL LEAD TO RENEWED CHANCES FOR SNOW...MAINLY NE WY LATE SUNDAY
NIGHT.

&&

.LONG TERM...MONDAY THROUGH SATURDAY
ISSUED AT 426 PM MST SAT NOV 22 2014

AN ACTIVE PATTERN ASSOCIATED WITH DEEP CYCLONIC FLOW ALOFT WILL
CONTINUE ACROSS THE NORTHERN HIGH PLAINS EARLY NEXT WEEK. SEVERAL
WEAK DISTURBANCES WITHIN NORTHWEST FLOW WILL SLIDE THROUGH...BRINGING
A GOOD DEAL OF CLOUDINESS AND CHANCES FOR SNOW SHOWERS AT TIMES
THROUGH WEDNESDAY. THE BEST CHANCES FOR SNOW WILL GENERALLY BE
ACROSS NORTHEAST WY AND THE NORTHERN BLACK HILLS AREA.

FOR THE HOLIDAY PERIOD...THE LATEST RUNS OF THE GFS...ECMWF...AND
CANADIAN HAVE ALL FLIPPED BACK TO A COLDER REGIME FOR LATE IN THE
WEEK AS A CANADIAN COLD FRONT IS PROGGED TO SLIDE SOUTH THROUGH THE
AREA LATE WEDNESDAY/WEDNESDAY NIGHT. WILL TREND COLDER AGAIN FOR
THANKSGIVING DAY AND THE REST OF THE EXTENDED...BUT UNCERTAINTY
STILL EXISTS WITH REGARD TO TEMPS. IT DOES CONTINUE TO LOOK MAINLY
DRY DURING THE PERIOD THOUGH.

&&

.AVIATION...FOR THE 00Z TAFS THROUGH 00Z SUNDAY EVENING
ISSUED AT 426 PM MST SAT NOV 22 2014

A COLD FRONT WILL CROSS THE AREA TONIGHT...WITH GUSTY NORTHWEST
WINDS DEVELOPING BEHIND THE FRONT. A FEW RAIN SHOWERS ARE
EXPECTED THIS EVENING OVER MAINLY NORTHEAST WY AND FAR WESTERN
SD...CHANGING TO SNOW SHOWERS OVERNIGHT. SOME AREAS OF MVFR
CONDITIONS ARE EXPECTED...ESPECIALLY ACROSS FAR NORTHEAST WY AND
THE BLACK HILLS. STRONGER NORTHWEST WINDS WILL DEVELOP ACROSS THE
AREA SUNDAY MORNING.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...WIND ADVISORY FROM 8 AM MST /9 AM CST/ TO 8 PM MST /9 PM CST/
     SUNDAY FOR SDZ014-025-027-032-041-043-044-046-047-049.

     HIGH WIND WARNING FROM 8 AM TO 8 PM MST SUNDAY FOR SDZ001-002-
     012-013-026-031-072-073.

WY...NONE.
&&

$$

UPDATE...HELGESON
SHORT TERM...JC
LONG TERM...26
AVIATION...26




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