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000
FXUS63 KUNR 070529
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
1029 PM MST FRI DEC 6 2013

.SHORT TERM...THIS EVENING THROUGH SATURDAY NIGHT
ISSUED AT 246 PM MST FRI DEC 6 2013

UPPER AIR ANALYSIS SHOWS BROAD TROUGHING OVER MUCH OF
NORTH AMERICA...AND A SHORTWAVE DIGGING INTO THE NORTHWEST CONUS. WINDS
ARE LIGHT AND VARIABLE...WHILE MIDLEVEL STRATUS CONTINUES TO MOVE
INTO THE REGION. TEMPERATURES ARE STRUGGLING TO RISE ABOVE ZERO
TODAY...AND WIND CHILLS ARE STILL -20 TO -30.

LOWS TONIGHT WILL AGAIN REACH -10 TO -25...WITH WIND CHILLS OF -25
TO -35. LIGHT SNOW IS POSSIBLE TONIGHT...MAINLY ACROSS NORTHEASTERN
WYOMING...THE BLACK HILLS...AND SOUTHWESTERN SOUTH DAKOTA...AS WARM
AIR OVERRUNS FRIGID SURFACE AIR. MINIMAL ACCUMULATIONS ARE EXPECTED.

THE SHORTWAVE WILL PUSH INTO OUR REGION SATURDAY...PRODUCING LIGHT
SNOW SATURDAY INTO SUNDAY. ACCUMULATIONS OF 1 TO 2 INCHES ARE POSSIBLE.
HIGHS SATURDAY WILL RANGE FROM 10 ABOVE ZERO ACROSS SOUTHERN SOUTH
DAKOTA TO 10 BELOW ZERO ACROSS THE NORTH. SOME AREAS MAY CONTINUE TO
EXPERIENCE BITTER WIND CHILLS INTO SATURDAY NIGHT...ESPECIALLY
ACROSS NORTHWESTERN SOUTH DAKOTA. WILL LET LATER SHIFTS DECIDE ON
EXTENDING THE WIND CHILL ADVISORY.

&&

.LONG TERM...SUNDAY THROUGH FRIDAY
ISSUED AT 246 PM MST FRI DEC 6 2013

OMEGA BLOCKING PATTERN WILL BREAKDOWN IN THE
PERIOD...TRANSITIONING TO WNW FLOW. DEEP WESTERN CONUS UPPER TROUGH
WILL LIFT ENE INTO THE PLAINS SUNDAY...WITH ASSOCIATED LIFT AND
REFLECTED LL SOUTHERLY FLOW SUPPORTING CHANCES FOR LIGHT SNOW.
DISTURBED NW FLOW WILL REMAIN THROUGH THE REMAINDER OF THE
PERIOD...WITH SOME UPSLOPE SNOW POSSIBLE IN THE NORTHERN BLACK
HILLS. THE SHIFT TO WNW FLOW...WILL SUPPORT WARMER TEMPS AS
DOWNSLOPE FLOW FROM THE ROCKIES WILL SPREAD INTO THE REGION BEHIND
PERIODIC CLIPPERS...EVENTUALLY SCOURING OUT THE ARCTIC AIRMASS IN
PLACE. HOWEVER...A PORTION OF THE ARCTIC AIRMASS WILL REMAIN IN
PLACE ACROSS CENTRAL CANADA...WITH A QUASI-STATIONARY BAROCLINIC
ZONE JUST NORTH OF THE REGION...SUPPORTING THE POTENTIAL FOR FAIRLY
COLD AIR /NOT TO THE DEGREE OF THE CURRENT COLD AIRMASS IN PLACE/ TO
SPREAD BACK INTO THE REGION LATE IN THE PERIOD OR BEYOND.

SUN...WESTERN CONUS TROUGH WILL SHIFT EAST AND SUPPORT INCREASING
DEEP LAYER ASCENT WITH A LL WAA RESPONSE...SUPPORTING CHANCES FOR
SNOW. DRY AIRMASS IN PLACE WITH DISMAL MOISTURE ADVECTION WILL LIMIT
AVAILABLE MOISTURE. PROGGED LIFT GENERALLY REMAINS ON THE COLD SIDE
OF THE DGZ...LIKELY SUPPORTING SMALL CRYSTAL SIZE. HENCE...NOT
EXPECTING MUCH IN THE WAY OF ACCUMS...WITH MOST PLACES SEEING LESS
THAN ONE INCH OF LIGHT SNOW. SCENTRAL COULD SEE AN INCH OR 2 GIVEN
PROXIMITY TO BETTER LIFT AND MOISTURE. DID ADJUST POPS UP IN THE
PERIOD...WITH MAINLY A HIGH POP LOW QPF EVENT.

MON-TUE...A CLIPPER SYSTEM WILL ADVECT EAST...NORTH OF THE
REGION...GRAZING THE NORTHERN CWA. AS OF RIGHT NOW...FORECAST MODELS
ARE MAINLY SUPPORTING AN UPSLOPE SNOW RESPONSE IN THE FA...WITH THE
REMAINDER OF THE FA NOT SEEING MUCH IF ANY PRECIP...SAVE NW SD. HAVE
RETAINED POPS ACROSS FAR NW SD AND THE NORTHERN BLACK HILLS...WITH A
MARGINAL TO DECENT PERIOD OF UPSLOPE FORCING POSSIBLE...ALTHOUGH
MOISTURE WILL BE LIMITED. DID ADJUST TEMPS DOWN SOME TUE NIGHT GIVEN
A STRONGER SOUTHWARD PUSH OF COLD AIR BEHIND THE CLIPPER.

TUE NIGHT-FRI...HEIGHT RISES EXPECTED THROUGH THUR AS FLOW
TRANSITIONS TO WESTERLY AND ANOTHER CLIPPER SYSTEM ADVECTS THROUGH
THE REGION. DID ADD A LIGHT SNOW MENTION TO MOST OF THE FA TUE
NIGHT...AS A LL FRONTAL ZONE WILL BE IN PLACE...AND WILL SLOWLY
BEGIN TO LIFT NE. ROCKIES DOWNSLOPE AIR WILL ADVECT INTO THE
REGION...WITH WARMER TEMPS EXPECTED...ESP BY THUR. HAVE REMAINED
LEARY OF WARMING THINGS UP TO QUICKLY...WITH THE FORECAST MODELS
SEEMINGLY TOO AGGRESSIVE WITH SCOURING OUT LL COLD AIR...ESP ON THE
SD PLAINS. KEPT THE WARMEST READINGS MAINLY CONFINED TO THE HIGHER
TERRAIN /NE WY AND THE BLACK HILLS/ THUR. COLD FRONT WILL PUSH INTO
THE AREA FRI WITH SOME MODEL DISAGREEMENT PER THE THE DEGREE OF CAA.
00Z ECMWF SUPPORTED A STRONGER INTRUSION OF COLD AIR ALONG WITH THE
12Z AND 06Z GFS. HOWEVER...THE GENERALLY MORE RELIABLE ECMWF HAS
TRENDED WARMER FOR FRI...DELAYING MORE SUBSTANTIAL CAA UNTIL THE
WEEKEND. HAVE TRENDED IN THIS DIRECTION.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SATURDAY NIGHT)
ISSUED AT 1027 PM MST FRI DEC 6 2013

ARCTIC ST WILL CONTINUE TO DEVELOP OVER THE AREA THROUGH
SATURDAY OVER NORTHEAST WY/SOUTHWEST SD. MVFR CIGS WILL RESULT
WITH LOCAL IFR CIGS/VSBYS DUE TO -SN. CIGS OVER NORTHWEST SD WILL
BE SLOWER TO SHIFT FROM VFR TO MVFR...BUT SHOULD OCCUR BY MIDDAY
SATURDAY.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...WIND CHILL ADVISORY UNTIL NOON MST /1 PM CST/ SATURDAY FOR
     SDZ001-002-012>014-024>032-041>044-046-047-049-072>074.

WY...WIND CHILL ADVISORY UNTIL NOON MST SATURDAY FOR WYZ054>058-071.

&&

$$

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