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000
FXUS63 KUNR 021717
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
1017 AM MST MON DEC 2 2013

.UPDATE...
ISSUED AT 1014 AM MST MON DEC 2 2013

NW-SE BAND OF MID-LEVEL INSTABILITY EXITS FROM SOUTHEASTERN MT
INTO FAR NERN WY AND PARTS OF WRN SD. ISOLATED -SHRA WILL BE POSSIBLE
IN THOSE AREAS THROUGH THE AFTERNOON.

&&

.SHORT TERM...TODAY THROUGH TUESDAY NIGHT
ISSUED AT 428 AM MST MON DEC 2 2013

CURRENT SURFACE ANALYSIS SHOWS FRONTAL BOUNDARY/WARM FRONT FROM
WESTERN ND THROUGH CENTRAL SD. ARCTIC FRONT IS APPROACHING THE
CANADIAN/MT BORDER. UPPER LEVEL ANALYSIS SHOWS STRONG WEST-
NORTHWEST FLOW ALOFT OVER THE REGION...WITH A SERIES OF WEAK
DISTURBANCES CROSSING THE NORTHERN ROCKIES AND PLAINS. AN UPPER
LOW IS LOCATED OVER SOUTHERN BC...SLIDING SLOWLY SOUTH AND EAST.
SKIES ARE VARIABLY CLOUDY ACROSS THE AREA...WITH THE MOST CLOUDS
ACROSS NORTHERN AND WESTERN PORTIONS OF THE CWA AT THIS TIME.
REGIONAL RADARS SHOW PCPN WITH ONE DISTURBANCE NOW EAST OF THE
CWA...WHILE SOME PCPN...MOSTLY LIGHT RAIN...IS MOVING ACROSS
CENTRAL MT AND NORTH CENTRAL WY. TEMPS ARE IN THE 30S AND LOWER
40S AT MOST LOCATIONS. WINDS ARE FROM THE WEST-SOUTHWEST...LOCALLY
BREEZY ACROSS WESTERN AREAS.

ONE MORE MILD DAY IS ON TAP...WITH HIGHS IN THE UPPER 40S AND 50S...
BEFORE THE ARCTIC AIR ARRIVES TONIGHT AND REMAINS ENTRENCHED ACROSS
THE REGION FOR AT LEAST THE NEXT WEEK. UNSETTLED WEATHER CAN ALSO BE
EXPECTED WITH THE ARRIVAL OF THE ARCTIC AIR AS UPPER LOW/TROF OVER
THE PACIFIC NW SLIDES EAST ACROSS THE NORTHERN ROCKIES AND PLAINS
THROUGH MIDWEEK. IT IS A RATHER DIFFICULT FORECAST FOR THE NEXT
COUPLE OF DAYS...COMPLICATED BY THE CONSISTENT INCONSISTENCY OF THE
MODELS. LATEST MODEL RUNS CONTINUE TO DIVERGE TOO MUCH WITH REGARD
TO THE TRACK AND EVOLVEMENT OF THIS SYSTEM OVER THE NEXT COUPLE OF
DAYS. ECMWF WAS GENERALLY THE MOST CONSISTENT OF THE MODELS OVER THE
LAST FEW DAYS...BUT THE LATEST RUN HAS DIVERGED SIGNIFICANTLY FROM
ITS PREVIOUS RUNS AS WELL AS THE OTHER MODELS. HOWEVER...LOCAL WRF
MODELS ARE IN DECENT AGREEMENT WITH THE LATEST NAM AND GFS FOR THE
NEXT 24 TO 36 HRS...SO HAVE DECIDED TO FOLLOW A GENERAL BLEND OF
THESE FOR THIS FORECAST. THIS IS NOT A WHOLE LOT DIFFERENT THAN
PREVIOUS FORECASTS HAVE DEPICTED...BUT GIVES A BIT MORE CONFIDENCE
ON MORE SIGNIFICANT ACCUMULATIONS OF SNOW FALLING ACROSS NORTHERN
PORTIONS OF THE CWA TONIGHT INTO TUESDAY BEHIND THE ARCTIC FRONT.

WITH THE INCREASED CONFIDENCE OF 2 TO 6 INCHES OF SNOW FALLING
ACROSS FAR NORTHEASTERN WY...THE NORTHERN BLACK HILLS...AND
NORTHWESTERN SD...HAVE DECIDED TO ISSUE A WINTER STORM WATCH FOR
SNOW AND BLOWING SNOW FOR THESE AREAS FROM LATER THIS EVENING INTO
WEDNESDAY. MOST OF THE SNOW WILL FALL TONIGHT INTO TUESDAY IN THESE
AREAS...BUT THE PROLONGED PERIOD OF THE WATCH ACCOUNTS FOR THE WINDY
CONDITIONS AND BLOWING SNOW THAT WOULD BE EXPECTED INTO WEDNESDAY.
FURTHER SOUTH...ESPECIALLY ACROSS SOUTHWEST AND SOUTH CENTRAL
SD...ANY SNOWFALL AMOUNTS LOOK TO BE LIGHT THROUGH AT LEAST MUCH OF
TUESDAY. THERE IS STILL PLENTY OF UNCERTAINTY REGARDING A SECONDARY
WAVE THAT IS PROGGED BY MOST MODELS TO SLIDE SOUTHEAST ACROSS THE
CENTRAL ROCKIES AND PLAINS LATER TUESDAY INTO WEDNESDAY. THE
NORTHERN EDGE OF THIS SYSTEM COULD IMPACT SOUTHERN PORTIONS OF THE
CWA WITH AT LEAST SOME LIGHT SNOW TUESDAY NIGHT INTO WEDNESDAY.

ARCTIC AIR WILL CONTINUE TO PUSH INTO THE AREA THROUGH WEDNESDAY
ONCE THE FRONT PASSES...ACCOMPANIED BY GUSTY NORTH-NORTHWEST WINDS.
TEMPS WILL FALL TO THE TEENS AND 20S BY TUESDAY MORNING...WITH TEMPS
CONTINUING TO SLOWLY FALL THROUGH THE DAY TUESDAY AND TUESDAY NIGHT.
LOWS BY WEDNESDAY MORNING WILL BE IN THE SINGLE DIGITS ABOVE AND
BELOW ZERO...WITH WIND CHILLS WELL BELOW ZERO. WILL LIKELY NEED
WINTER WX...WIND...AND/OR WIND CHILL HEADLINES FOR THE REST OF THE
AREA AT SOME POINT OVER THE NEXT FEW DAYS.

&&

.LONG TERM...WEDNESDAY THROUGH SUNDAY
ISSUED AT 428 AM MST MON DEC 2 2013

CYCLONIC FLOW WILL CONTINUE WEDNESDAY WITH CONTINUED COLD AIR
ADVECTION AND A REASONABLY TIGHT PRESSURE GRADIENT. LEFTOVER -SN
CHANCES WILL CONTINUE...ESPECIALLY IN NORTHEAST WY/NORTHWEST SD
WHERE SOME BLSN WILL CONTINUE THROUGH WEDNESDAY AFTERNOON. ARCTIC
HIGH PRESSURE WILL THEN BUILD INTO THE AREA WEDNESDAY NIGHT WITH
VERY COLD TEMPERATURES.

THURSDAY THROUGH SUNDAY...ARCTIC AIR WILL REMAIN ENTRENCHED ACROSS
THE CWA WITH MASSIVE UPPER TROUGH OVER CENTRAL NORTH AMERICA.
SURFACE HIGH WILL BE CENTERED OVER THE NORTHERN PLAINS. WEAK WARM
AIR ADVECTION OVER THE SURFACE HIGH MAY BRING SOME -SN TO THE AREA
FRIDAY NIGHT INTO THE WEEKEND.

&&

.AVIATION...FOR THE 12Z TAFS THROUGH 12Z TUESDAY MORNING
ISSUED AT 428 AM MST MON DEC 2 2013

ISOLATED RAIN SHOWERS ARE EXPECTED THROUGH THE AFTERNOON OVER
PARTS OF FAR NERN WY AND WRN SD. LCL MVFR CIGS ARE POSSIBLE IN ANY
-SHRA...OTHERWISE VFR CONDITIONS WILL PREVAIL INTO THE EVENING.
A STRONG ARCTIC COLD FRONT WILL RACE ACROSS THE AREA TONIGHT
BRINGING STRONG NORTHWEST WINDS...WIDESPREAD IFR/LIFR ST AND IFR
VSBYS DUE TO -SN AND BLSN.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...WINTER STORM WATCH FROM THIS EVENING THROUGH WEDNESDAY AFTERNOON
     FOR SDZ002-013-014-072-073.

     WINTER STORM WATCH FROM 8 PM MST THIS EVENING THROUGH WEDNESDAY
     AFTERNOON FOR SDZ001-012-024-025.

WY...WINTER STORM WATCH FROM 8 PM MST THIS EVENING THROUGH WEDNESDAY
     MORNING FOR WYZ054>057-071.

&&

$$

UPDATE...10
SHORT TERM...26
LONG TERM...HELGESON
AVIATION...HELGESON