Area Forecast Discussion
Issued by NWS Rapid City, SD

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000
FXUS63 KUNR 311556
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
856 AM MST SAT JAN 31 2015

.UPDATE...
ISSUED AT 823 AM MST SAT JAN 31 2015

POTENT WINTER STORM TAKING SHAPE ACROSS THE MID COUNS THIS
MORNING. PHASING NORTHERN AND SOUTHERN STREAM UPPER TROUGHS WILL
SUPPORT CYCLOGENESIS ACROSS THE CENTRAL PLAINS THIS
AFTERNOON...WITH A DEVELOPING DEFORMATION ZONE NW OF THE LOW. THIS
DEFORMATION ZONE IS PROGGED TO AFFECT SOUTH CENTRAL SD LATE THIS
AFTERNOON INTO TONIGHT. ABUNDANT MOISTURE WILL AVAILABLE WITH THIS
SYSTEM SUPPORTING A PERIOD OF DECENT SNOWS AS LIFT EXPANDS ACROSS
THE REGION TONIGHT. CURRENT EXPECTATION IS FOR 3-4 INCHES ACROSS
MUCH OF TRIPP COUNTY...WITH LOCALLY HIGHER AMOUNTS POSSIBLE ACROSS
THE SOUTHEAST PORTION OF THE COUNTY. HAVE ISSUED A WW ADV FOR
THIS.

&&

.SHORT TERM...TODAY THROUGH SUNDAY NIGHT
ISSUED AT 349 AM MST SAT JAN 31 2015

UPPER LEVEL ANALYSIS HAS UPPER LOW ACROSS THE SOUTHWEST CONUS WITH
NORTHWEST FLOW ACROSS THE NORTHERN CONUS. SKIES ARE CLOUDY ACROSS
THE NORTHERN PLAINS WITH LOW STRATUS DECK SLIDING SOUTH ACROSS THE
DAKOTAS. AT THE SURFACE...BACK-DOOR COLD FRONT IS CURRENTLY
DROPPING SOUTH ACROSS SOUTH DAKOTA...WITH WINDS TURNING NORTHEAST
BEHIND THE FRONT. TEMPERATURES ARE MAINLY IN THE 20S.

TODAY...UPPER RIDGE SHIFTS SOUTHEAST AS CUT-OFF LOW DEVELOPS
ACROSS THE SOUTHWEST CONUS. SURFACE COLD FRONT AND STRATUS DECK
WILL CONTINUE TO DROP SOUTHWEST ACROSS THE WESTERN SOUTH DAKOTA
PLAINS. COOLER AIR WILL FILTER INTO THE AREA BEHIND THE
FRONT...AND ALONG WITH THE CLOUD COVER...AREAS ACROSS THE SOUTH
DAKOTA PLAINS WILL REMAIN IN THE 20S FOR TODAY. FURTHER WEST IN
WYOMING...HIGH TEMPERATURES WILL BE MILDER...IN THE LOWER 40S.
STRONG NORTHERN STREAM IMPULSE WILL SLIDE THROUGH THE NORTHERN
PLAINS LATE TODAY INTO TONIGHT. THIS FEATURE WITH AN ASSOCIATED
STRONG JET STREAK WILL FORCE A PERIOD OF LIGHT SNOW OVER THE AREA
TONIGHT. IN ADDITION...A DEVELOPING SURFACE LOW WILL SKIRT SOUTH
CENTRAL SOUTH DAKOTA...SUPPORTING A SEPARATE AREA OF SNOW.
OVERALL...SNOW TOTALS WILL BE LIGHT...IN THE 1-3 INCH
RANGE...HIGHEST ACROSS THE NORTHERN BLACK HILLS AND ACROSS TRIPP
COUNTY.

SUNDAY...UPPER SHORTWAVE SHIFTS QUICKLY EAST...WITH SOME LIGHT
SNOW POSSIBLY LINGERING ACROSS THE NORTHERN BLACK HILLS AND FAR
SOUTH CENTRAL SOUTH DAKOTA DURING THE MORNING. WEAK UPPER RIDGE
BUILDS ACROSS THE ROCKIES WITH SKIES BECOMING MOSTLY SUNNY LATE
IN THE DAY. ARCTIC HIGH REMAINS ACROSS THE AREA WITH HIGH
TEMPERATURES ONLY IN THE TEENS ACROSS THE SOUTH DAKOTA
PLAINS...AND IN THE 20S ACROSS NORTHEAST WYOMING. LOWS SUNDAY
NIGHT WILL FALL INTO THE 5 TO 20 DEGREE RANGE.

.LONG TERM...MONDAY THROUGH FRIDAY
ISSUED AT 349 AM MST SAT JAN 31 2015

NW FLOW ALOFT WILL CONTINUE OVER THE FORECAST AREA THROUGH THE
EXTENDED FORECAST PERIOD...BECOMING MORE ZONAL TOWARD THE END OF
THE WEEK. A RELATIVELY WEAK SHORTWAVE WILL BRING A SLIGHT CHANCE
OF SNOW OR RAIN TO THE FORECAST AREA ON MONDAY AND TUESDAY. A
BETTER DEFINED UPPER TROUGH WILL AFFECT THE AREA ON TUESDAY NIGHT
AS A COLD FRONT MOVES THROUGH AT THE SURFACE...BRINGING A CHANCE
OF SNOW TO THE AREA. AT THIS TIME IT LOOKS LIKE THE BEST AREA FOR
MEASURABLE SNOW ACCUMULATION WOULD BE OVER PARTS OF NORTHEASTERN
WYOMING AND SOUTHWESTERN SOUTH DAKOTA. DRY WEATHER IS THEN
EXPECTED THROUGH THE REST OF THE WEEK.

THE TEMPERATURE FORECAST REMAINS TRICKY AS A SURFACE FRONTAL
BOUNDARY FLUCTUATES ACROSS THE FORECAST AREA WITH A WIDE VARIATION
IN TEMPERATURES ON EITHER SIDE OF THE BOUNDARY. AT THIS TIME IT LOOKS
LIKE HIGH TEMPERATURES WILL MAINLY BE SLIGHTLY WARMER THAN AVERAGE
ON MONDAY AND TUESDAY...THEN BECOMING COLDER THAN AVERAGE BEHIND THE
COLD FRONT ON WEDNESDAY. THE BOUNDARY WILL THEN SHIFT NORTHEASTWARD
AGAIN WITH MUCH WARMER THAN AVERAGE TEMPERATURES EXPECTED ON FRIDAY.

&&

.AVIATION...FOR THE 12Z TAFS THROUGH 12Z SUNDAY MORNING
ISSUED AT 349 AM MST SAT JAN 31 2015

AREA OF IFR/MVFR STRATUS OVER NERN AND NCNTRL SD WILL SINK INTO
WESTERN SOUTH DAKOTA THIS MORNING...REACHING THE BLACK HILLS
AROUND 15Z THEN CONTINUING TO SINK SOUTHWEST THROUGH THIS EVENING.
LIGHT SNOW WILL SPREAD ACROSS MUCH OF THE AREA FROM LATE THIS
AFTERNOON THROUGH TONIGHT...RESULTING IN WIDESPREAD IFR
CONDITIONS.


&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...WINTER WEATHER ADVISORY FROM 4 PM THIS AFTERNOON TO 6 AM CST
     SUNDAY FOR SDZ049.

WY...NONE.
&&

$$

UPDATE...JC
SHORT TERM...15
LONG TERM...10
AVIATION...10






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