FXUS63 KUNR 152104
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
200 PM MST TUE DEC 15 2009

.DISCUSSION...CURRENT SURFACE ANALYSIS PLACES LOW PRESSURE OVER 
SOUTHERN ALBERTA...WITH HIGH CENTERED OVER EASTERN NEBRASKA. STRONG 
TEMPERATURE GRADIENT REMAINS OVER THE CWFA...AS SHALLOW COLD AIRMASS 
OVER THE SOUTH DAKOTA PLAINS IS RELUCTANT TO GO ANYWHERE...WHILE THE 
HIGHER ELEVATIONS OF NORTHEAST WYOMING AND THE BLACK HILLS CONTINUE 
TO WARM UP. UPPER LEVEL ANALYSIS PLACES BROAD RIDGE OVER THE WESTERN 
CONUS.

FOR TONIGHT...UPPER RIDGE OVER THE REGION WILL KEEP QUIET WEATHER IN 
PLACE. STRONG TEMPERATURE INVERSION DUE TO SHALLOW COLD AIRMASS WILL 
REMAIN...WITH WARM OVER THE HILLS AND COLD OVER THE SODAK PLAINS.

ON WEDNESDAY...RIDGE AXIS SLIDES EAST AS SHALLOW COLD AIRMASS 
RETRACTS OUT OF THE AREA. NEAR TO ABOVE AVERAGE TEMPERATURES ARE 
EXPECTED...WITH THE WARMEST TEMPS OVER THE BLACK HILLS AREA AND NERN 
WYO.

FOR THURSDAY...SHORT WAVE PUSHES THROUGH AND FLATTENS OUT THE 
RIDGE...BRINGING SLIGHTLY COOLER TEMPERATURES ALONG WITH A CHANCE 
FOR PRECIPITATING. 

EXTENDED...BIG MODEL DIFFERENCES ARE NOTED FROM FRIDAY INTO TUESDAY. 
RMOP SHOWS LOW PREDICTABILITY OVER THE NORTHERN PLAINS WITH 
SIGNIFICANT DIFFERENCES EXISTING IN THE ENSEMBLE MEMBER SOLUTIONS. 
12Z OPERATIONAL GFS MODEL IS SHOWING SIGNIFICANT SNOWFALL FROM 
SATURDAY NIGHT THROUGH SUNDAY NIGHT...HOWEVER THAT SOLUTION IS NOT 
SUPPORTED BY THE MAJORITY OF THE GFS ENSEMBLE MEMBERS OR BY THE 
ECMWF. WILL WAIT AND SEE IF THE LATER MODEL RUNS CONTINUE TO POINT 
TO THAT SOLUTION BEFORE MAKING SIGNIFICANT CHANGES TO THE FORECAST

&&

.AVIATION...VFR CONDITIONS EXPECTED OVERNIGHT.

&&

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

&&

$$