Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 251628
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
928 AM MST THU DEC 25 2014

.UPDATE...
ISSUED AT 913 AM MST THU DEC 25 2014

UPPER TROUGH CONTINUES TO SHIFT EASTWARD OVER THE ROCKIES...AND
SURFACE LOW IS OVER NORTHEASTERN CO. RADAR SHOWS SNOW OVER MUCH OF
WESTERN SD...GRADUALLY MOVING SOUTHEASTWARD. OBS INDICATE SNOW
OVER NORTHEASTERN WY AS WELL. HAVE RECEIVED A REPORT FROM BUTTE
COUNTY OF AN INCH OF SNOW SO FAR...WITH LESS THAN AN INCH IN THE
RAPID CITY AREA AT THIS TIME. APPEARS THAT RADAR IS GREATLY
OVERESTIMATING SNOWFALL AMOUNTS. TEMPS ARE IN THE UPPER 20S TO
LOWER 30S...AND ARE EXPECTED TO DECREASE THROUGH THE DAY. OTHER
THAN MAKING SOME MINOR TWEAKS TO THE POPS TO MATCH CURRENT RADAR
THIS MORNING...NO OTHER UPDATES TO THE FORECAST ARE NECESSARY.

&&

.SHORT TERM...TODAY THROUGH FRIDAY NIGHT
ISSUED AT 328 AM MST THU DEC 25 2014

WATER VAPOR IMAGERY SHOWS A DEEP TROUGH STRENGTHENING ACROSS THE
WESTERN CONUS WITH THE AXIS/DEVELOPING CUTOFF LOW NOW CROSSING THE
GREAT BASIN. SURFACE ANALYSIS SHOW LOW PRESSURE STRENGTHENING ACROSS
THE CNTRL TO NRN HIGH PLAINS. KUDX RADAR SHOWS SNOW HAS DEVELOPED
MAINLY NORTH OF INTERSTATE 90 AND IT GRADUALLY EXPANDING IN
COVERAGE.

UPPER TROUGH WILL CONTINUE TO DEVELOP TODAY INTO A CUT OFF LOW OVER
THE GREAT BASIN WITH STRONG FORCING OVER WY INTO WRN SD/NEB. BAND OF
SNOW WILL SLIDE SOUTH THROUGH THE DAY...AT A FASTER PACE THAN MODELS
HAD BEEN SHOWING PREVIOUSLY. NOW IT APPEARS SNOW WILL CLEAR NW SD
QUITE EARLY THIS MORNING IF NOT ALREADY...AND BE MORE FOCUSED ON THE
BLKHLS TO SCNTRL SD BY THE AFTN HOURS. SNOW WILL THEN CONTINUE TO
WORK THROUGH THE SRN CWA THIS EVNG AND TAPER OFF OVER SCNTRL LATE
TONIGHT. SNOW AMOUNTS STILL APPEAR TO BE IN LINE WITH 3 TO 6 INCHES
OF ACCUMULATION...WITH A FEW AREAS POSSIBLE GETTING SLIGHTLY HIGHER
AMOUNTS. ONE OF THOSE AREAS MAY BE THE NORTHERN BLACK HILLS. A COLD
FRONT WILL CROSS THE AREA TODAY WITH NW WINDS 15-20KT BEHIND THE
FRONT. AS A RESULT...UPSLOPE CONDITIONS WILL DEVELOP OVER THE NRN
HILLS. HOWEVER...UPSLOPING WILL BE RELATIVELY WEAK...BUT IT MAY BE
ENOUGH TO PRODUCE AN ADDITIONAL INCH OR TWO OVER THE NRN HILLS.
THERE WILL BE SOME BLOWING SNOW...BUT IT ISNT EXPECTED TO BE
SIGNIFICANT.

THE UPPER LOW WILL PUSH ACROSS THE FOUR CORNERS FRIDAY WITH THE BEST
LIFT STAYING S/SE OF THE CWA. SURFACE HIGH PRESSURE WILL BUILD OVER
THE NRN PLAINS WITH COLDER TEMPS OVER THE REGION. HIGHS WILL REACH
THE UPPER TEENS TO MID 20S...WITH SOME MIX OF SUN AND CLOUDS
EXPECTED.

.LONG TERM...SATURDAY THROUGH WEDNESDAY
ISSUED AT 328 AM MST THU DEC 25 2014

PERSISTENT NORTHWEST FLOW WILL BE FOUND ACROSS THE AREA FOR
EXTENDED PERIOD AS RIDGE BUILDS ACROSS THE NORTHEAST PACIFIC INTO
ALASKA. THIS WILL FAVOR INTRUSIONS OF ARCTIC AIR INTO THE NORTHERN
PLAINS...WITH BELOW AVERAGE TEMPERATURES. SATURDAY WILL FEATURE
INCREASING CLOUDS WITH WEAK MID LEVEL WAA. SHORTWAVE DIGS INTO THE
NORTHERN ROCKIES/GREAT BASIN SUNDAY INTO MONDAY. BROAD AREA OF
ISENTROPIC LIFT SETS UP ACROSS THE AREA LATE SUNDAY INTO SUNDAY
NIGHT. MEANWHILE...ARCTIC AIR SPILLS THROUGH SOUTHERN
CANADA...REACHING WESTERN SOUTH DAKOTA SUNDAY NIGHT. BLUSTERY AND
MUCH COLDER ON MONDAY. A FEW INCHES OF SNOW POSSIBLE SUNDAY
NIGHT/MONDAY. 1050+ MB ARCTIC HIGH SETTLES IN OVER AREA FOR
TUESDAY...WITH HIGHS 20-30F BELOW AVERAGE. SOME MODERATION IN
TEMPERATURES FOR WEDNESDAY/THURSDAY.

&&

.AVIATION...FOR THE 12Z TAFS THROUGH 12Z FRIDAY MORNING
ISSUED AT 328 AM MST THU DEC 25 2014

WIDESPREAD IFR CIGS/VSBYS EXPECTED FOR MUCH OF THE DAY WITH
SNOWFALL...ESPECIALLY ALONG AND SOUTH OF INTERSTATE 90. THE SNOW
WILL END FROM NORTH TO SOUTH LATE THIS AFTERNOON/EVENING.
HOWEVER...MVFR/IFR CIGS WILL PERSIST THROUGH TONIGHT.


&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...WINTER WEATHER ADVISORY UNTIL 11 PM MST THIS EVENING FOR SDZ012-
     013-024>032-041-072>074.

     WINTER WEATHER ADVISORY UNTIL 5 AM MST /6 AM CST/ FRIDAY FOR
     SDZ042>044-046-047-049.

WY...WINTER WEATHER ADVISORY UNTIL 11 PM MST THIS EVENING FOR
     WYZ054>058-071.

&&

$$

UPDATE...POJORLIE
SHORT TERM...13
LONG TERM...7
AVIATION...7






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