FXUS65 KRIW 240954
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
254 AM MST THU DEC 24 2009

.SHORT TERM...TODAY THROUGH SATURDAY NIGHT

GFS AND NAM IN FAIRLY GOOD AGREEMENT THROUGH THE SHORT TERM FORECAST 
PERIOD. DEEP UPPER LOW WILL MOVE SOUTHEASTWARD TODAY FROM EASTERN MT 
INTO WESTERN SD. NORTHWEST CYCLONIC FLOW AROUND THE UPPER LOW WILL 
PREDOMINATE ACROSS WESTERN AND CENTRAL WY TODAY. THERE WILL BE 
ENOUGH LOW AND MID LEVEL MOISTURE EAST OF THE DIVIDE TODAY TO 
DEVELOP ISOLATED BANDS OF LIGHT SNOW WITH LITTLE TO ONLY MINOR 
ACCUMULATIONS. AS THE UPPER LOW CONTINUES TO MOVE SOUTHEASTWARD 
TONIGHT AND FRIDAY...IT WILL MERGE WITH THE UPPER LOW OVER THE 
SOUTHERN PLAINS AND FORM A MASSIVE UPPER LOW OVER CENTRAL MO BY 00Z 
SATURDAY. NAM...GFS AND GEFS PROJECT THAT MOISTURE ROTATING AROUND 
UPPER LOW CIRCULATION IN THE PLAINS WILL BRING INCREASING MID LEVEL 
MOISTURE AND AN AXIS OF MID LEVEL UPWARD VERTICAL MOTION ACROSS 
EASTERN CENTRAL WY LATE TONIGHT AND FRIDAY. LIGHT SNOW WITH MINOR 
ACCUMULATIONS IS EXPECTED ACROSS JOHNSON AND NATRONA COUNTIES 
TONIGHT THROUGH FRIDAY EVENING. THE BEST CHANCE FOR STEADY SNOWFALL 
ACROSS THESE AREAS WILL BE FROM 06Z FRIDAY THROUGH 18Z FRIDAY. 
UPSLOPE ENHANCEMENT OF LIGHT SNOW COULD PRODUCE A FEW INCHES OF SNOW 
ON CASPER MOUNTAIN TONIGHT THROUGH FRIDAY AFTERNOON...BUT LOWER 
ELEVATIONS OF JOHNSON AND NATRONA COUNTIES WILL LIKELY RECEIVE LESS 
THAN ONE INCH OF SNOW. AS THE UPPER LOW LIFTS NORTHEASTWARD ACROSS 
THE UPPER MIDWEST FRIDAY NIGHT THROUGH SATURDAY NIGHT...DRIER AIR 
FROM THE WEST WILL MOVE ACROSS WY. TEMPERATURES THROUGH THE PERIOD 
FROM TODAY THROUGH SATURDAY NIGHT WILL BE BELOW NORMAL WITH DAYTIME 
HIGHS 10 TO 15 F BELOW NORMAL. 

.LONG TERM...SUNDAY THROUGH THURSDAY
MODELS BEGINNING TO CONVERGE ON A SOLUTION THAT MAY ACTUALLY
WORK OUT IN THE MEDIUM RANGE PERIOD. THE DETAILS STILL VARY WIDELY
BUT AT LEAST THE SOLUTIONS ARE MUCH CLOSER THAN LAST NIGHT. AT THE 
BEGINNING OF THE PERIOD...IT APPEARS WE WILL SEE THE HIGH OVER LOW
SCENARIO AS CLOSED UPPER HIGH SITS OVER SRN CANADA AND A NEW LOW 
DIGS INTO THE DESERT SW EARLY NEXT WEEK. IT APPEARS THIS SYSTEM 
WILL BE TOO FAR SOUTH FOR ANY SNOW THIS FAR NORTH. BY THE MIDDLE
OF NEXT WEEK...THE MODELS ARE CONSOLIDATING THE FLOW SOME AND 
BRINGING A DISTURBANCE INTO THE STATE FOR WEDNESDAY. THE GFS SHOWS 
MORE OF A SMALL CLOSED LOW DIGGING INTO THE AREA WHILE THE ECMWF HAS 
A MOIST NW FLOW WITH AN EMBEDDED DISTURBANCE. THE GEM AT 144 HOURS 
FAVORS THE ECMWF. LEANED TOWARDS THE ECMWF TONIGHT AND BEGAN 
INTRODUCING CHANCE POPS IN THE WEST WEDNESDAY AND A SLIGHT
CHANCE EAST OF THE DIVIDE WEDNESDAY NIGHT. FORECAST LOOKS DRY AND
SEASONABLY COLD SUNDAY AND MONDAY WITH SOME MOUNTAIN FLURRIES OR
LIGHT SNOW POSSIBLE AS EARLY AS TUESDAY IN THE NW MTNS.

&&

.AVIATION...

LOW PRESSURE WILL MOVE TO THE EAST OF WYOMING EARLY THIS MORNING 
THROUGH THIS EVENING. SKIES WILL BECOME PARTLY CLOUDY ACROSS WESTERN 
AND CENTRAL WYOMING BEFORE DAWN TODAY WITH MVFR VISIBILITY IN FOG 
POSSIBLE AT KJAC AFTER 12Z AND IFR VISIBILITY AT KRIW. AS LOW 
PRESSURE STRENGTHENS IN THE WEST CENTRAL PLAINS TODAY...WEST 
SOUTHWEST WIND AT KCPR WILL GUST TO AROUND 25 KT AND WEST WIND AT 
KRKS WILL GUST TO NEAR 35 KT AT KRKS THIS AFTERNOON. VFR CONDITIONS 
WILL PREVAIL TODAY...AS HIGH PRESSURE BUILDS INTO THE REGION FROM 
THE NORTHWEST. 

&&

.FIRE WEATHER...

NORTHWEST FLOW ALOFT AND WEST TO NORTHWEST FLOW IN THE LOWER LEVELS 
OF THE ATMOSPHERE WILL BRING DRIER AIRMASS INTO WYOMING TODAY 
THROUGH FRIDAY. TEMPERATURES TODAY AND FRIDAY WILL BE 10 TO 15 F 
BELOW NORMAL WITH AN ABSENCE OF LATE NIGHT AND EARLY MORNING 
INVERSIONS. WEST TO SOUTHWEST WIND WITH GUSTS TO BETWEEN 25 AND 35 
MPH TODAY ARE EXPECTED IN THE WIND CORRIDOR FROM WESTERN SWEETWATER 
COUNTY EAST NORTHEASTWARD ACROSS NATRONA COUNTY.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$

SHORT TERM...SMITH
LONG TERM...SKRBAC
AVIATION...SMITH
FIRE WEATHER...SMITH