Area Forecast Discussion
Issued by NWS Rapid City, SD

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000
FXUS63 KUNR 152335
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
435 PM MST MON DEC 15 2014

.SHORT TERM...THIS EVENING THROUGH TUESDAY NIGHT
ISSUED AT 213 PM MST MON DEC 15 2014

UPPER LEVEL ANALYSIS HAS LOW CENTER OVER IOWA SLIDING NORTHEAST.
UPPER RIDGE IS SLOWLY BUILDING ACROSS THE ROCKIES AS EAST PACIFIC
TROF APPROACHES THE WEST COAST. SKIES ACROSS THE NORTHERN PLAINS
RANGE FROM MOSTLY SUNNY OVER WESTERN AREAS...TO CLOUDY WITH LIGHT
SNOW FROM THE CENTRAL DAKOTAS EAST. AT THE SURFACE...CANADIAN
HIGH PRESSURE CONTINUES TO SLIDE SOUTH INTO THE AREA. NORTHWEST
WINDS CONTINUE TO BE QUITE BREEZY...WITH WINDS JUST BEGINNING TO
SLACKEN ACROSS NORTHEAST WYOMING. TEMPERATURES AT 2 PM ARE IN THE
20S.

TONIGHT...DRY AIR MOVES IN QUICKLY TONIGHT BEHIND THE EXITING
SYSTEM...AND PRECIP WILL END ACROSS SOUTH CENTRAL SOUTH DAKOTA BY
EARLY EVENING. HOWEVER...SOME AREAS OF CLOUDS AND SOME PATCHY FOG
WILL STICK AROUND THROUGH THE NIGHT. WITH MAINLY PARTLY CLOUDY
CONDITIONS OVERNIGHT...LOW TEMPERATURES WILL FALL INTO THE SINGLE
DIGITS AND TEENS.

TUESDAY...WESTERN UPPER RIDGE WILL CROSS THE NORTHERN PLAINS AS
THE CANADIAN SURFACE HIGH SHIFTS INTO THE EASTERN DAKOTAS. NORTH
WINDS WILL BE LIGHT...AND SLOWLY SHIFT AROUND OUT OF THE SOUTH BY
LATE AFTERNOON. HIGHS WILL BE IN THE 20S TO LOWER 30S...WITH LOWS
TUESDAY NIGHT AROUND 10 TO 20. SKIES WILL BECOME CLOUDIER
OVERNIGHT AHEAD OF AN APPROACHING UPPER TROUGH.

.LONG TERM...WEDNESDAY THROUGH MONDAY
ISSUED AT 213 PM MST MON DEC 15 2014

PROGRESSIVE SPLIT FLOW PATTERN TO PERSIST THROUGH THE LONG TERM
PERIOD. MAINLY DRY WX EXPECTED THROUGH THE PERIOD GIVEN TROUGH RE-
LOADING IN THE WESTERN CONUS. HOWEVER...ANOTHER STRONG SOUTHERN
PERIPHERY UPPER TROUGH WILL EJECT OUT OF THE SW CONUS IN THE THU-
FRI PERIOD. FORECAST MODELS ARE NOW LATCHING ONTO THE EJECTION OF
A PRIMARY FRONT SIDE IMPULSE. THIS SYSTEM WOULD BRING A SMALL
CHANCE FOR LIGHT SNOW ACROSS THE FAR NW FA WED AS IT INTERACTS
WITH THE LL BAROCLINIC ZONE IN PLACE. THIS SYSTEM IS PRESENT IN
ALL FORECAST MODELS ALTHOUGH THE TRACK IS STILL IN QUESTION.
INCLUDED A LOW POP ACROSS THE NW WED FOR THIS. THE MAIN SW CONUS
UPPER TROUGH CONTINUES TO BE ADVERTISED TO TRACK JUST SOUTH OF THE
FA TOWARD THE END OF THE WEEK. IF ANY NORTHERN STREAM IMPULSES
TEND TO PHASE WITH THIS SYSTEM...A TRACK FARTHER NW COULD STILL BE
POSSIBLE...WHICH COULD BRING SOME CHANCES FOR SNOW TO SCENTRAL
AREAS ONCE AGAIN TOWARD FRIDAY-SAT. TENDENCIES FOR ANOTHER STRONG
WESTERN NOAM RIDGE REMAIN PRESENT IN MEAN ENSEMBLES AND
DETERMINISTIC SOLUTIONS PER ANOTHER EXTENSION OF THE EAST ASIAN
UPPER JET. THIS COULD SPELL MUCH WARMER CONDITIONS FOR THE
FOLLOWING WEEK IF THE RIDGE BIASES EAST AS IT HAS IN THIS PATTERN.
HOWEVER...CURRENT LONG RANGE ECMWF/GFS RUNS STILL SUPPORT A CLOSED
LOW IN THE PACIFIC NEAR HAWAII WITH A DOMINATE NORTHERN
STREAM...UNCHARACTERISTIC OF THE CURRENT REGIME. THE 12Z ECMWF HAS
NOW SHIFTED THE RIDGE SLIGHTLY NE WITH THE BAROCLINIC ZONE RIGHT
ON TOP OF THE FA. THIS HEIGHT PATTERN LOOKS VERY SIMILAR TO THE
THANKSGIVING DAY PATTERN 7-10 DAYS OUT WITH A LARGE RANGE IN TEMPS
AMONG DETERMINISTIC SOLUTIONS MID NEXT WEEK.

GIVEN STRONGER PROGRESSIVE TENDENCIES...FORECAST MODELS SUPPORT
WARMER WESTERLY FLOW INTO THE REGION A LITTLE EARLIER THAN BEFORE.
HENCE...HAVE WARMED TEMPS SOME IN THE LATTER PORTION OF THE PERIOD.
OTHERWISE...NO OTHER SIG CHANGES TO THE FORECAST.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z TUESDAY EVENING)
ISSUED AT 426 PM MST MON DEC 15 2014

UPPER LOW AND ASSOCIATED SNOWS WILL END ACROSS THE AREA THIS
EVENING. IFR CIGS ON THE SD PLAINS WILL TREND TO MVFR AND LIKELY
REMAIN THROUGH MUCH OF THE PERIOD. FURTHER WEST...CLEAR SKIES
WILL LIKELY REMAIN OVER THE BLACK HILLS AND ADJACENT PLAINS.
HOWEVER...MVFR CIGS ARE EXPECTED TO STRADDLE THE RAP
TERMINAL GIVEN MOIST NW FLOW...CONFIRMED IN HIRES GUIDANCE. THERE
IS THE POTENTIAL FOR CLEARING AT THE RAP TERMINAL.
HOWEVER...HIGHEST CONFIDENCE IS IN CONTINUED MVFR CIGS. LOW CIGS
OVER THE WY PLAINS MAY LINGER INTO LATE TUE MORNING UNTIL DRY LL
SW FLOW CAN BECOME ESTABLISHED. RAP MODEL INDICATES POTENTIAL
CLEARING EARLIER...HOWEVER CONFIDENCE IN THIS REMAINS LOW GIVEN
HIRES GUIDANCE. WILL KEEP WITH IFR CIGS ATTM MONITORING TRENDS FOR
POTENTIAL AMENDMENTS. CIGS WILL BE DIFFICULT LATE IN THE PERIOD
TUE AFTERNOON AS THE SFC RIDGE AXIS WILL BE OVER THE FA. THIS WILL
LIKELY HINDER STRATUS MIX OUT WITH MANY PLACES LIKELY SEEING MVFR
CIGS.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...WINTER WEATHER ADVISORY UNTIL 6 PM CST THIS EVENING FOR SDZ046-
     047-049.

WY...NONE.
&&

$$

SHORT TERM...15
LONG TERM...JC
AVIATION...JC






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