Area Forecast Discussion
Issued by NWS Rapid City, SD

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000
FXUS63 KUNR 312050
AFDUNR

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

.SHORT TERM...THIS EVENING THROUGH SUNDAY NIGHT
ISSUED AT 148 PM MST SAT JAN 31 2015

POTENT WINTER STORM TAKING SHAPE ACROSS THE MID CONUS.
PHASING NORTHERN AND SOUTHERN STREAM UPPER TROUGHS WILL SUPPORT
CYCLOGENESIS ACROSS THE CENTRAL PLAINS...WITH A DEVELOPING
DEFORMATION ZONE NW OF THE LOW. THE FA WILL SEE INFLUENCE FROM BOTH
OF THESE SYSTEMS WITH THE NORTHERN COUNTERPART AFFECTING MOST OF
THE FA...WHILE SCENTRAL SD WILL SEE AN INFLUENCE FROM BOTH. BACKDOOR
COLD FRONT HAS SPREAD SW ACROSS THE FA...WITH FG AND AREAS OF ZL IN
ITS WAKE. EXPECTING FG AND ZL TO TAPPER OFF LATE THIS AFTERNOON AND
EARLY EVENING AS THERMAL PROFILES COOL AND ICE NUCLEATION ENSUES.
IN ADDITION...SEEDER FEEDER FROM DEVELOPING SNOWS WILL ALSO SCOUR
AVAILABLE NUCLEI. MAIN STORY WILL BE SNOWS TONIGHT. STRONG UPPER
JET STREAK ASSOCIATED WITH THE NORTHERN STREAM SHORTWAVE WILL COMBINE
WITH AN ASSOCIATED ARCTIC FRONT TO SUPPORT SNOWS ACROSS MOST OF EH
FA TONIGHT...SPREADING QUICKLY SE FROM NW SD THIS EVENING. MUCH OF
WESTERN SD AND PORTIONS OF NE WY WILL SEE AROUND AN INCH TO 2 INCHES
OF SNOW...POSSIBLY NEAR 3 IN THE FAR NE NEAR LEMMON. THE NORTHERN
BLACK HILLS AND FOOTHILLS WILL ALSO SEE SOME UPSLOPE
ENHANCEMENT...WITH CLOSER TO 3 INCHES POSSIBLE THERE. MOST OF THE
SNOW WILL FALL THIS EVENING...WITH RESIDUAL LIGHT SNOW THE REMAINDER
OF THE NIGHT.

A LITTLE DIFFERENT PROCESS EXPECTED OVER SCENTRAL SD. MASSIVE SW
CONUS UPPER LOW WILL EJECT INTO THE CENTRAL PLAINS AND CONTINUE TO
SUPPORT VIGOROUS CYCLOGENESIS IN THE EASTERN CENTRAL PLAINS AND
MIDWEST. MOIST CONVEYOR BELT ASSOCIATED WITH THIS PROCESS WILL
SUPPORT A STRENGTHENING DEFORMATION ZONE ACROSS CENTRAL NE INTO
SCENTRAL SD TONIGHT...WHERE LOCALLY ENHANCED SNOW RATES CAN BE
EXPECTED. IN ADDITION...PHASING NORTHERN STREAM IMPULSE WILL SUPPORT
A BRIEF STALL/PIVOT OF THE MOISTURE CONVEYOR BELT AND ASSOCIATED
DEFORMATION ZONE/FGEN...SUPPORTING A 2-4 HOUR EXTENSION OF DECENT
SNOWFALL. BOTTOM LINE EXPECTING 2-5 INCHES ACROSS MELLETTE...TODD
AND ESP TRIPP COUNTIES. LOCALLY HIGHER AMOUNTS COULD BE POSSIBLE IF
THE ENTIRE PROCESS SHIFTS A BIT FARTHER NW AND PAUSES LONGER. SNOW
WILL WIND DOWN QUICKLY SUNDAY MORNING WITH CLEARING SUNDAY AFTERNOON
MOST IF NOT ALL PLACES. A BRIEF SKIRT OF ARCTIC AIR WILL SUPPORT
MUCH COLDER TEMPERATURES ACROSS THE FA THROUGH SUNDAY. ACTIVE NW FLOW
WILL PERSIST WITH A LL BAROCLINIC ZONE REMAINING ACROSS THE FA. THE
NEXT IN A SERIES OF IMPULSES WILL ARRIVE LATE SUNDAY NIGHT...AND MAY
SUPPORT SNOW TOWARD DAWN MONDAY ACROSS THE FAR NW.

.LONG TERM...MONDAY THROUGH SATURDAY
ISSUED AT 148 PM MST SAT JAN 31 2015

NW FLOW ALOFT WILL CONTINUE OVER THE FORECAST AREA
THROUGH THE EXTENDED FORECAST PERIOD. A RELATIVELY WEAK SHORTWAVE
WILL BRING A CHANCE OF SNOW OR RAIN TO THE FORECAST AREA ON MONDAY
AND TUESDAY. A BETTER DEFINED UPPER TROUGH/JET STREAK 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.
SNOW MAY LINGER INTO WEDNESDAY ACROSS THE SOUTHWESTERN CWA...BUT DRY
WEATHER IS THEN EXPECTED THROUGH THE REST OF THE WEEK AS A RIDGE
BUILDS OVER THE WESTERN CONUS.

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...ESPECIALLY ACROSS THE SOUTHWEST HALF OF THE
CWA. BELOW NORMAL TEMPS ARE EXPECTED ON WEDNESDAY AS THE BOUNDARY
SHIFTS SOUTH. WESTERLY WINDS WILL AID IN SIGNIFICANT WARMING FOR THE
END OF THE WEEK.

&&

.AVIATION...FOR THE 18Z TAFS THROUGH 18Z SUNDAY
ISSUED AT 148 PM MST SAT JAN 31 2015

FOG AND -FZDZ OVER MUCH OF WESTERN SD WILL CREATE
IFR/LIFR CIGS/VSBY THROUGH THE AFTERNOON. LIGHT SNOW WILL SPREAD
ACROSS THE AREA LATE THIS AFTERNOON THROUGH TONIGHT...RESULTING IN
WIDESPREAD IFR CONDITIONS. CIGS/VSBY WILL IMPROVE SUNDAY MORNING AS
SNOW TRANSITIONS EASTWARD.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...WINTER WEATHER ADVISORY UNTIL 6 AM CST SUNDAY FOR SDZ046-047-049.

WY...NONE.
&&

$$

SHORT TERM...JC
LONG TERM...POJORLIE
AVIATION...POJORLIE





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