FXUS63 KUNR 020926
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
226 AM MST WED DEC 2 2009

.DISCUSSION...WATER VAPOR IMAGERY CONTINUES TO SHOW A DEEP LONGWAVE 
TROUGH ACROSS THE NORTHERN PLAINS BRINGING VERY COLD AIR TO THE 
REGION. 09Z SURFACE ANALYSIS PLACE A STRONG 1030 MB HIGH PRESSURE 
RIDGE ACROSS NORTHWEST WYOMING THROUGH WESTERN MONTANA. NORTHWEST 
WINDS WILL CONTINUE TODAY...THOUGH PRESSURE GRADIENT IS MORE RELAXED 
THAN YESTERDAY...SO ADVISORY CRITERIA WINDS ARE NOT AGAIN EXPECTED. 
WINDS WILL STILL BE IN THE 15 TO 25 MPH RANGE ESPECIALLY ACROSS THE 
SOUTH DAKOTA PLAINS. A COLD AND MOIST AIRMASS OVER THE REGION WILL 
BRING MUCH COLDER TEMPERATURES TO THE REGION WITH HIGHS IN THE 20S. 
A MOIST AND UNSTABLE AIRMASS WILL BRING SNOW SHOWERS TO MUCH OF THE 
AREA TODAY. NOT MUCH QPF EXPECTED WITH THESE SHOWERS. THE EXCEPTION 
IS ACROSS THE NORTHERN BLACK HILLS WHERE UPSLOPING CONDITIONS ARE 
EXPECTED. SOME PARTS OF THE NORTHERN HILLS COULD SEE ONE TO THREE 
INCHES OF SNOW BY LATE TONIGHT. MODELS INDICATE THE BEST CHANCE FOR 
SNOW WILL BE LATE THIS AFTERNOON THROUGH THE EARLY EVENING AS AN 
EMBEDDED WAVE CROSSES THE AREA. SNOW SHOWERS WILL CONTINUE THURSDAY 
ACROSS THE AREA...BUT GRADUALLY DECREASE THROUGH THE DAY. THE PRECIP 
WILL BE OVER BY THURSDAY EVENING WITH MAYBE ANOTHER INCH POSSIBLE 
OVER THE NORTHERN HILLS. HIGHS THURSDAY WILL STRUGGLE TO REACH THE 
20 DEGREE MARK ACROSS THE CWA...WITH SOME PARTS ACROSS NORTHEAST 
WYOMING...NORTHWEST SOUTH DAKOTA...AND THE BLACK HILLS ONLY SEEING 
HIGHS IN THE MID TO UPPER TEENS. WEAK UPPER RIDGING WILL BUILD 
ACROSS THE REGION FRIDAY AS DRIER AIR MOVES INTO THE AREA. WARMER 
AIR WILL BEGIN ADVECTING IN FROM THE WEST...SO MAX TEMPS WILL BE 
WARMER. HIGHS IN THE MID 20S TO LOWER 30S ARE EXPECTED FRIDAY.

EXTENDED...GFS/ECMWF/GEM REMAIN IN AGREEMENT OVER THE WEEKEND INTO 
EARLY NEXT WEEK WITH UPPER TROF DIGGING ACROSS THE NRN ROCKIES. EVEN 
WITH SOME SPREAD BETWEEN THE MODELS IN 850/700MB TEMPS...ALL THREE 
MODELS ARE SHOWING A 1030+MB HIGH DROPPING INTO THE NRN PLAINS BY 
MONDAY. DUE TO THE COLD HIGH PRESSURE COMBINED WITH EXPECTED CLOUD 
COVER...WILL TREND TOWARDS LOWER END OF GUIDANCE TEMPERATURES. WITH 
UPPER TROF DIGGING TO THE WEST OF THE AREA...THERE WILL BE A PERIOD 
OF WEST-SOUTHWEST FLOW FROM 700-500MB WHICH SHOULD RESULT IN SOME 
ISENTROPIC LIFT OVER ARCTIC AIR. WILL CONTINUE WITH LOW POPS FOR NOW 
AS MOISTURE APPEARS TO BE LACKING. 

&&

.AVIATION...MAINLY VFR CONDITIONS WITH ISOLD-SCT -SHSN EXPECTED 
TODAY WITH THE EXCEPTION OF NORTHWESTERN SOUTH DAKOTA AND OVER THE 
BLACK HILLS WHERE MVFR CIGS ARE EXPECTED.

&&

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

$$

CALDERON/RICHARDS