FXUS63 KUNR 111741
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
1030 AM MST FRI DEC 11 2009

.DISCUSSION...HAVE PUSHED TEMPERATURES UP OVER THE BLACK HILLS INTO 
THE EASTERN/NORTHERN FOOTHILLS...AS WARMER AIR ALOFT COMBINED WITH 
LIGHT DOWNSLOPE WINDS HAVE QUICKLY PUSHED TEMPERATURES INTO THE 
MID/UPPER 20S IN SOME LOCATIONS. HAVE ALSO BACKED OFF ON CLOUD COVER 
SINCE MOST LOCATIONS REMAIN CLEAR. UPDATE WILL BE OUT SHORTLY. 

PREVIOUS DISCUSSION...09Z SURFACE ANALYSIS HAS ARCTIC HIGH PRESSURE 
OVER THE GREAT PLAINS WITH WEAK LEE TROF FROM THE CANADIAN ROCKIES 
TO THE FRONT RANGE OF COLORADO. TEMPERATURES AROUND ZERO TO 15 ABOVE 
WITH LIGHT WEST TO SOUTHWEST WINDS. UPPER LEVEL ANALYSIS HAS 
CYCLONIC FLOW OVER THE NORTHERN CONUS WITH RIDGE OVER THE EASTERN 
PACIFIC. 

MODELS CONTINUE TO SHOW THE CYCLONIC FLOW ALOFT TRANSITIONING
INTO A MORE ZONAL FLOW HEADING INTO THE WEEKEND. BOUNDARY LAYER
FLOW TURNS MORE SOUTHWESTERLY TODAY...ALLOWING SOME WARMER AIR TO
WORK INTO WESTERN PORTIONS OF THE AREA. LOCATIONS ACROSS THE
PLAINS WILL ONLY SEE SLIGHTLY WARMER TEMPERATURES TODAY AS ARCTIC
AIR WILL BE HARD TO COMPLETELY SCOUR OUT. HIGHS ARE EXPECTED TO BE
IN THE LOWER 20S ACROSS NORTHWEST AND CENTRAL SOUTH DAKOTA...AND
UPPER 20S TO AROUND 30 ACROSS SOUTHWEST SOUTH DAKOTA THROUGH THE
BLACK HILLS INTO NORTHEAST WYOMING.

ANOTHER QUIET DAY IS EXPECTED ON SATURDAY. A WEAK SHORTWAVE WILL
TRACK TO THE NORTH OF THE AREA...BUT A BACK DOOR COLD FRONT WILL
SLIDE INTO THE NORTHWESTERN PART OF SOUTH DAKOTA...KEEPING
TEMPERATURES IN THE TEEN TO LOWER 20S THERE. WESTERN AREAS WILL
WARM WELL INTO THE 20S AND 30S.

ANOTHER STRONG UPPER LEVEL TROF WILL SLIDE SOUTH OUT OF CANADA ON
SUNDAY. SURFACE LOW DEVELOPS ACROSS SOUTHEAST WYOMING AS STRONG
COLD FRONT DROPS THROUGH THE NORTHERN PLAINS. MODELS SHOW A MID
LEVEL SHORTWAVE SLIDE ACROSS THE AREA AHEAD OF THE MAIN UPPER
TROF. THIS WAVE COULD POSSIBLY BRING SOME ACCUMULATING SNOW TO
PARTS OF NORTHEASTERN WYOMING AND WESTERN SOUTH DAKOTA ON SUNDAY.

EXTENDED...GOOD AGREEMENT WITH MODELS ON NEXT SHOT OF ARCTIC AIR FOR 
MONDAY/MONDAY NIGHT. GEM/ECMWF/GFS/GFS ENSEMBLE MEMBERS SHOW 
1035-1045MB HIGH DROPPING THROUGH THE DAKOTAS MONDAY NIGHT. LITTLE 
RECOVERY IN TEMPERATURES MONDAY GIVEN STRONG CAA. LIGHT 
SNOW/FLURRIES EXPECTED THROUGH THE DAY. GIVEN CURRENT TEMPERATURES 
IN SOURCE REGION OF THE HIGH...SHOULD SEE LOWS TUESDAY MORNING FROM 
-10F TO -20F. THIS SHOT OF COLD AIR SHOULD BE SHORT LIVED AS UPPER 
RIDGE WILL BE QUICK TO BUILD ACROSS THE NORTHERN ROCKIES. TEMPS 
SHOULD WARM TO ABOVE AVERAGE READINGS TOWARDS THE END OF NEXT WEEK.

&&

.AVIATION...VFR CONDITIONS THROUGH TODAY.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...NONE.
WY...NONE.
&&

$$