Area Forecast Discussion
Issued by NWS Rapid City, SD

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000
FXUS63 KUNR 242139
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
239 PM MST TUE FEB 24 2015

.SHORT TERM...THIS EVENING THROUGH WEDNESDAY NIGHT
ISSUED AT 238 PM MST TUE FEB 24 2015

UPPER AIR ANALYSIS SHOWS DEEP UPPER LOW ACROSS THE DESERT SW...WITH
STRONG RIDGING ACROSS THE NW PACIFIC COAST. NW FLOW REMAINS ACROSS
THE NRN PLAINS BEHIND A SECOND UPPER LOW NEAR HUDSON BAY. SURFACE
ANALYSIS SHOWS STRONG HUDSON LOW WITH ARCTIC FRONT STRETCHING ACROSS
THE UPPER MIDWEST INTO CNTRL ND...AND BACK NW INTO THE CANADIAN HIGH
PLAINS.

AN UPPER WAVE NOW OVER BC CNDA WILL SLIDE SE INTO THE NRN
ROCKIES/NRN PLAINS. INITIAL BAND OF PRECIP WILL DEVELOP ACROSS NE
MT/WRN ND THIS EVNG AND SHORT RANGE MODELS NOW AGREE PRECIP WILL
SLIDE MAINLY INTO CNTRL SD TONIGHT CLIPPING PORTIONS OF NW SD. SNOW
WITH THIS BAND IS EXPECTED TO LEAVE AN INCH OR LESS OF ACCUMULATION
ACROSS PORTIONS OF PERKINS AND ZIEBACH COUNTIES. INITIAL WEAK FRONT
WILL CROSS THE CWA LATER TONIGHT WITH RAIN DEVELOPING ACROSS THE
CWA...CHANGING TO SNOW THROUGH THE NIGHT. UPSLOPING CONDITIONS WILL
DEVELOP LATE TONIGHT ENHANCING SNOWFALL THROUGH EARLY WED MORNING.

SNOW WILL CONTINUE ACROSS THE AREA WED MORNING WITH THE BEST CHANCES
CONTINUING ACROSS THE NRN BLKHLS. THE ARCTIC FRONT WILL CROSS THE
AREA MAINLY THROUGH THE AFTN HOURS WITH TEMPS FALLING THROUGH THE
DAY. AS DRIER AIR MOVES IN...PRECIP WILL GRADUALLY END ACROSS THE
WRN SD PLAINS THROUGH THE AFTN...AND ACROSS THE NE WY PLAINS AND
BLKHLS WED NIGHT. GENERALLY 1-2 INCHES OF ACCUMULATION ARE EXPECTED
ACROSS THE WRN SD PLAINS...WITH 1-3 INCHES OF THE NE WY
PLAINS...WITH SOME SLIGHTLY HIGHER AMOUNTS POSSIBLE. STILL LOOKS
LIKE THE NRN HILLS AREA COULD SEE 3 TO 7 INCHES BY LATE WED EVNG.
GUSTY NRLY WINDS WILL DEVELOP THROUGH THE DAY WITH AREAS OF BLOWING
SNOW EXPECTED MAINLY ACROSS NW SD TO THE PLAINS EAST OF THE BLKHLS.
12Z MODEL RUNS HAVE SLIGHTLY BACKED OFF WITH WIND SPEEDS TOMORROW
WHICH TAKES IT TO A VERY MARGINAL WIND ADVISORY THRESHOLD. AT THIS
POINT DONT THINK ANY NPW HEADLINES WILL BE NEEDED...BUT WILL LET
MIDSHIFT SEE IF THAT TREND CONTINUES WITH THE 00Z MODEL RUN.

.LONG TERM...THURSDAY THROUGH TUESDAY
ISSUED AT 238 PM MST TUE FEB 24 2015

PERSISTENT NW FLOW WILL SUPPORT A COLD AND
SEMI-UNSETTLED EXTENDED PERIOD. MAIN LOBE OF ARCTIC AIR WILL BE OVER
THE REGION THU BEHIND A STRONG NW FLOW UPPER TROUGH. WESTERN NOAM
RIDGE THAT HAS BEEN POSITIONED JUST WEST OF THE REGION WILL
BREAKDOWN AND SHIFT WEST...WITH LARGE SCALE NORTHERLY FLOW REMAINING
IN PLACE INTO NEXT WEEK. MAINLY DRY WX EXPECTED THROUGH THE PERIOD
AFTER WED...AS DRY NORTHERLY FLOW PREVAILS. THE FA REMAINS ON THE
FAR NORTH EDGE OF THE EJECTING SW CONUS SYSTEM WITH LITTLE LOCAL
IMPACT EXPECTED...GIVEN STRONG TENDENCIES FOR PROGRESSIVE NW FLOW
AND AN AGGRESSIVE SFC RIDGE. OVERALL...SIDED MORE TOWARD THE COLDER
SIDE OF GUIDANCE WITH THE FIRST ARCTIC INTRUSION WED-FRI...WITH A
TREND TOWARD THE MIDDLE IF GUIDANCE INTO THE WEEKEND GIVEN FLOW
MODERATION AND LACK OF SIG TEMP ANOMALIES.

COLD AIR WILL SETTLE INTO THE REGION THUR...WITH TEMPS AVERAGING
20-30 DEGREES BELOW SEASONAL NORMS. SOME MODERATION IN TEMPS
EXPECTED FRI-SAT AND AGAIN MON WITH WEAK RIDGING AHEAD OF PROGGED NW
FLOW UPPER TROUGHS. FORECAST MODELS HAVE TRENDED MUCH WARMER MON
GIVEN A NOW PROGGED MORE PRONOUNCED NW PAC TROUGH AND ASSOCIATED
STRONG WAA SURGE. TRENDED POPS SOUTH IN THE SAT PERIOD...WITH MOST
AREAS NOT SEEING A WX MENTION...GIVEN A MORE AGGRESSIVE SFC RIDGE
BUILDING INTO THE REGION. POTENTIALLY BETTER PRECIP CHANCES MAY
ARRIVE TOWARD THE BEGINING OF NEXT WEEK AS MORE AGGRESSIVE/AMPLIFIED
NW FLOW BECOMES ESTABLISHED.

&&

.AVIATION...FOR THE 00Z TAFS THROUGH 00Z WEDNESDAY EVENING
ISSUED AT 238 PM MST TUE FEB 24 2015

MVFR CIGS WILL DEVELOP IN A BAND LOCATED FROM NORTHWESTERN INTO
SOUTH CENTRAL SOUTH DAKOTA LATE THIS AFTERNOON. THERE IS A CHANCE
OF RAIN OR SNOW SHOWERS OVER FAR NORTHWESTERN SOUTH DAKOTA THIS
AFTERNOON. VFR CONDITIONS ARE EXPECTED ACROSS THE REST OF THE AREA
TODAY. MVFR CIGS WILL COVER MOST OF NORTHEASTERN WYOMING AND THE
WESTERN HALF OF SOUTH DAKOTA TONIGHT WITH AREAS IFR /LOCAL VLIFR/
CONDITIONS IN -SN. MVFR/IFR CONDS WILL PERSIST THROUGH MOST OF
WEDNESDAY.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...WINTER WEATHER ADVISORY FROM MIDNIGHT TONIGHT TO MIDNIGHT MST
     WEDNESDAY NIGHT FOR SDZ024-025.

WY...WINTER WEATHER ADVISORY FROM MIDNIGHT TONIGHT TO MIDNIGHT MST
     WEDNESDAY NIGHT FOR WYZ057.

&&

$$

SHORT TERM...13
LONG TERM...JC
AVIATION...JC






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