Area Forecast Discussion
Issued by NWS Rapid City, SD

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000
FXUS63 KUNR 250338
AFDUNR

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

.UPDATE...
ISSUED AT 830 PM MST TUE FEB 24 2015

03Z SURFACE ANALYSIS HAD LOW OVER BELLE FOURCHE SD...RIDING ALONG
FRONTAL BOUNDARY FROM NORTHEAST MT INTO CENTRAL NE. LIFT AHEAD OF
LOW UNDER RIGHT ENTRANCE REGION OF 110KT JET PRODUCING BAND OF
PRECIPITATION FROM ABOUT LEMMON TO NEAR WINNER...MAINLY TURNING TO
SNOW BY MIDNIGHT. FURTHER WEST...SHORTWAVE ENERGY DROPPING DOWN
INTO MT...WHICH WILL PROVIDE FORCING FOR SECOND ROUND OF
PRECIPITATION MOVING ACROSS THE CWA FROM NORTH TO SOUTH LATER
TONIGHT THROUGH WEDNESDAY AFTERNOON. MIGHT START OUT AS SOME
RAIN...BUT AS SURFACE LOW SHIFTS SOUTHEAST...ARCTIC AIR WILL
BEGIN TO POUR INTO THE CWA LATE TONIGHT/EARLY WEDNESDAY MORNING
CHANGING PRECIPITATION TO ALL SNOW. UPSLOPE ENHANCEMENT LIKELY
OVER THE NORTHERN BLACK HILLS FROM 12Z WEDNESDAY UNTIL 06Z
THURSDAY.

CURRENT FORECAST HAS GOOD HANDLE ON THESE FEATURES...SO WILL ONLY
TWEAK FOR LATEST TRENDS.

&&

.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 BEGINNING OF NEXT WEEK AS MORE AGGRESSIVE/AMPLIFIED
NW FLOW BECOMES ESTABLISHED.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z WEDNESDAY NIGHT)
ISSUED AT 830 PM MST TUE FEB 24 2015

ARCTIC BOUNDARY WILL SHIFT THROUGH THE AREA LATE TONIGHT/EARLY
WEDNESDAY BRINGING WIDESPREAD MVFR/IFR CIGS AND GUSTY NORTHERLY
WINDS THROUGH WEDNESDAY. AREAS -SN WILL DEVELOP WITH LIFR
VSBYS/CIGS AT TIMES.

&&

.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.

&&

$$

UPDATE...HELGESON
SHORT TERM...13
LONG TERM...JC
AVIATION...HELGESON





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