FXUS63 KUNR 302034
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
134 PM MST MON NOV 30 2009

.DISCUSSION...CURRENT WATER VAPOR IMAGERY SHOWS NORTHWEST FLOW ALOFT 
ACROSS THE CWA WITH SHORTWAVE TROUGH MOVING INTO THE PACIFIC 
NORTHWEST. COLD FRONT WILL PUSH ACROSS THE CWA TUESDAY MORNING AS 
TROUGH HEADS FOR THE CWA. EXPECT A MODERATE PRESSURE GRADIENT TO SET 
UP ACROSS THE BLACK HILLS TONIGHT. THE PRESSURE DIFFERENCE WILL
BE AROUND 4 MB WITH BOUNDARY LAYER WINDS AROUND 30 KTS. THIS WILL
CREATE GUSTY SOUTHWEST WINDS ACROSS THE NORTHERN FOOTHILLS MAINLY
FROM CROW PEAK TO SPEARFISH TO STURGIS. EXPECT WINDS OF 15 TO 30
MPH TO DEVELOP ACROSS THESE AREAS WITH A FEW GUSTS TO AROUND 40
MPH. EXPECT THE SOUTHWEST WINDS TO STAY BELOW ADVISORY CRITERIA. A
PRESSURE GRADIENT WILL ALSO SET UP ACROSS NORTHEAST WYOMING
CREATING GUSTY SOUTHWEST WINDS THIS EVENING. EXPECT GRADIENT TO
WEAKEN AFTER MIDNIGHT BRINGING AN END TO THE SOUTHWEST WINDS.
WINDS WILL SWITCH TO THE NORTHWEST EARLY TUESDAY MORNING AS COLD
FRONT PUSHES ACROSS THE AREA.

ON TUESDAY...GUSTY NORTHWEST WINDS WILL DEVELOP BEHIND THE FRONT 
ACROSS THE SOUTH DAKOTA PLAINS. WITH STRONG COLD AIR ADVECTION AND A 
STRONG PRESSURE GRADIENT...EXPECT WINDS TO BE IN ADVISORY RANGE WITH 
NORTHWEST WINDS AROUND 20 TO 30 MPH WITH GUSTS AROUND 55 MPH. THE 
STRONGEST WINDS WILL BE FOUND FROM K2WX TO KRAP. GIVEN THE EXPECTED 
WINDS...WILL ISSUE A WIND ADVISORY FOR ALL OF NORTHWEST SOUTH DAKOTA 
AND THE WEST CENTRAL SOUTH DAKOTA PLAINS FROM 7 AM TO 5 PM
TUESDAY. WITH TROUGH SWINGING THROUGH THE AREA...EXPECT A FEW SNOW
SHOWERS TO DEVELOP ACROSS NORTHEAST WYOMING AND WESTERN SOUTH
DAKOTA. MOISTURE WILL BE VERY LIMITED WITH THIS SYSTEM BUT GIVEN
THE STEEP LAPSE RATES EXPECT SNOW SHOWERS TO DEVELOP.

ON WEDNESDAY...THE CHANCE FOR SNOW SHOWERS WILL CONTINUE AS CYCLONIC 
FLOW SETS UP ACROSS THE AREA AND COLD AIR FILTERS INTO THE REGION. SOME 
UPSLOPE ENHANCEMENT CAN BE EXPECTED ACROSS THE NORTHERN BLACK 
HILLS...BUT WITH LIMITED MOISTURE EXPECT SNOW ACCUMULATIONS TO BE ON 
THE LIGHT SIDE. EXPECT SNOW SHOWERS TO TAPER OFF WEDNESDAY NIGHT AS 
COLD SFC HIGH PRESSURE BUILDS INTO THE CWA. LOW TEMPS ON WEDNESDAY 
NIGHT ARE EXPECTED TO RANGE FROM THE SINGLE DIGITS TO LOWER TEENS 
ACROSS MUCH OF THE CWA. 

EXTENDED...UPPER TROF ACROSS THE NORTH CENTRAL U.S. ON THURSDAY WITH 
CORE OF COLD TEMPERATURES AFFECTING THE FORECAST AREA. 850/700MB 
TEMPERATURES RESULT IN HIGHS IN THE TEENS AND 20S. SOME SLIGHT 
WARMING ON FRIDAY AS COLDEST AIR PULLS EAST. TEMPERATURES BELOW 
AVERAGE FOR THE WEEKEND AS 1030+ MB ARCTIC HIGH SLIPS INTO THE 
NORTHERN PLAINS. GFS/ECMWF/GEM DIFFER ON PLACEMENT/TIMING/STRENGTH 
OF NEXT UPPER TROF DIGGING INTO THE WESTERN U.S. WILL ADDED SOME 
SMALL POPS FOR NOW AS POTENTIAL EXISTS FOR SOME LIGHT SNOW.

&&

.AVIATION...VFR CONDITIONS ARE EXPECTED THROUGH TONIGHT. COLD FRONT 
WILL BLAST THROUGH THE AREA TUESDAY MORNING...WITH GUSTY NORTHWEST 
WINDS.
 
&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...WIND ADVISORY FROM 7 AM TO 5 PM MST TUESDAY FOR BUTTE-CUSTER CO 
     PLAINS-HAAKON-HARDING-HERMOSA FOOT HILLS-JACKSON-NORTHERN 
     FOOT HILLS-NORTHERN MEADE CO PLAINS-PENNINGTON CO PLAINS-
     PERKINS-RAPID CITY-SOUTHERN MEADE CO PLAINS-
     STURGIS/PIEDMONT FOOT HILLS-ZIEBACH.

WY...NONE.
&&

$$

JW/KC