FXUS65 KRIW 101039
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
339 AM MST THU DEC 10 2009

.SHORT TERM...TODAY THROUGH SATURDAY NIGHT
STRONG CYCLONIC NORTHWEST FLOW ALOFT WILL CONTINUE OVER WESTERN
AND CENTRAL WYOMING TODAY AND TONIGHT. WIND GUSTS AT THE RIVERTON
OFFICE MMTS ANEMOMETER REACHED 50KTS SEVERAL TIMES LATE WEDNESDAY
EVENING WITH WEST WIND IN THE 20-30KT RANGE CONTINUING EARLY THIS
MORNING. THE STRONG NORTHWEST FLOW WILL KEEP TEMPERATURES IN THE
WIND RIVER BASIN EASTWARD INTO NATRONA COUNTY UP ABOUT 15 TO 20
DEGREES FROM WEDNESDAY MORNING. RAISED HIGH TEMPERATURES FOR THESE
LOCATIONS THIS AFTERNOON AS A RESULT. ALSO INCREASED WEST
WIND...MAINLY FOR THE WIND RIVER BASIN...TODAY AND TONIGHT WITH
THE WIND MOMENTUM HAVING LITTLE TROUBLE REACHING THE BASIN FLOORS
DESPITE THE BITTER COLD. SIMILAR WIND SPEED AND DIRECTION ARE
EXPECTED THIS EVENING...FROM ABOUT CROWHEART TO RIVERTON WITH THE
GFS AND NAM BOTH PROGGING 35-40KTS OF WIND ONCE AGAIN AT H7. FLOW
BACKS TO DUE WESTERLY FRIDAY AFTERNOON...AND WITH A SOUTHWEST TO
NORTHEAST SFC PRESSURE GRADIENT...EXPECTING THE WIND WILL BEGIN TO
STRENGTHEN IN AREAS FAVORED BY SOUTHWEST FLOW...SUCH AS CODY AND
LANDER FOOTHILLS. MODELS CONTINUE TO TREND TO LESS IN THE WAY OF
ISENTROPIC UPGLIDE SNOWFALL OVER THE WEST-CENTRAL AND NORTHWEST
AREAS TODAY AND TONIGHT. LOWERED SNOW CHANCES AS A RESULT OF THE
LACK OF MID-LEVEL MOISTURE OVER CENTRAL AND SOUTHERN IDAHO.
INCREASED SNOW CHANCES FOR THE BIGHORN MTS THIS EVENING WITH
FAVORABLE NORTHWEST JET MOVING OVER THIS AREA. ALSO INTRODUCED
SLIGHT CHANCE POPS FOR THE NORTHERN BIG HORN BASIN WHERE THIS FLOW
TENDS TO PRODUCE MORE IN THE WAY OF JET INDUCED SNOW SHOWERS THAN
THE MODELS WOULD INDICATE.

SUBTROPICAL JET PROGGED TO UNDERCUT THE HIGH AMPLITUDE RIDGE OVER
THE EASTERN PACIFIC FRIDAY NIGHT. PACIFIC MOISTURE ASSOCIATED WITH
THIS JET AND SHORT-WAVE TROUGH BEGINS TO ADVECT INTO WESTERN
WYOMING FRIDAY AFTERNOON. AREAS OF LIGHT TO MODERATE SNOW EXPECTED
TO DEVELOP OVER THE FAR WEST DURING THE LATE EVENING. OCCASIONAL
LIGHT TO MODERATE SNOW WILL CONTINUE SATURDAY WITH WEAK TO
MODERATE ISENTROPIC UPLGLIDE CONTINUING OVER THE WEST. AS THE
SHORT-WAVE AND SUBTROPICAL JET STREAK MOVE INTO THE CENTRAL GREAT
BASIN SATURDAY NIGHT...SNOW COVERAGE AND INTENSITY WILL INCREASE
AS QG-FORCING AND LEFT FRONT QUAD JET DYNAMICS COMBINE WITH THE
PACIFIC MOISTURE. 

.LONG TERM...SUNDAY THROUGH THURSDAY
CHANCES OF SNOW CONTINUE ACROSS THE WEST AND SOUTH INTO SUNDAY AND
ACROSS THE WEST THROUGH THE REST OF THE PERIOD. OTHERWISE WARMING
TREND FORECAST TUESDAY THROUGH THURSDAY WITH DRY CONDITIONS ACROSS
THE CENTRAL AND SOUTH.

FORECAST CONTINUES TO REFLECT ECMWF OVERALL WITH BETTER SEPARATION
IN SPLIT FLOW EARLY IN THE PERIOD...KEEPING ARCTIC FRONT NORTH AND
EAST OF AREA BEHIND TROUGH PASSAGE SUNDAY NIGHT AND MONDAY.
LATEST GFS AND GEM SEEM TO BE TRENDING TOWARD ECMWF TONIGHT WITH
BETTER OVERALL AGREEMENT EARLY IN THE PERIOD. SECOND PACIFIC
TROUGH MOVES INTO THE GREAT BASIN SUNDAY WITH NORTHERN STREAM
STREAM SHORTWAVE ROUNDING BASE OF CENTRAL CANADIAN UPPER LOW
ACROSS MONTANA. WYOMING LARGELY CAUGHT IN BETWEEN THE TWO WITH
UNSTABLE NW FLOW KEEPING CHANCES OF SNOW SHOWERS ACROSS THE WEST
AND SOUTHERN WYOMING ON THE FRINGE OF PRECIPITATION FROM SOUTHERN
STREAM ENERGY. SPLIT TROUGHS MOVE INTO PLAINS MONDAY WITH FLAT
RIDGE TAKING SHAPE OVER WESTERN U.S. TUESDAY THROUGH THURSDAY.
PER ECMWF SOLUTION...GRADUAL AMPLIFICATION OF RIDGE THROUGH PERIOD
WILL RESULT IN OROGRAPHIC PRECIPITATION IN THE WEST LIFTING
NORTHWARD TO PRIMARILY YNP AND THE NW MOUNTAINS BY THURSDAY WITH
H7 TEMPERATURES NEAR 0C ACROSS THE AREA BY THURSDAY.
THUS...TEMPERATURES SHOULD RETURN TO ABOVE NORMAL TUESDAY THROUGH
THURSDAY WITH INVERSION PRONE WESTERN VALLEYS AND CENTRAL BASINS
FORECAST TO LAG 5F-10F BEHIND BETTER MIXED AREAS.  

&&

.AVIATION...
NORTHWEST WINDS OF 30G40KT WILL CONTINUE THROUGH 15Z AROUND KRIW 
THIS MORNING WITH SOME BLOWING SNOW.  SOUTHWEST TO WEST WINDS WILL 
INCREASE LATE THIS MORNING BETWEEN KRKS AND KCPR AS WELL AS AROUND 
KU25 PERSISTING THROUGH 00Z BEFORE DIMINISHING.  BKN MID CLOUDS ARE 
EXPECTED THROUGH 00Z OVER THE FAR WEST.  OTHERWISE NOT MUCH IN THE 
WAY OF CLOUD COVER EXPECTED OVER THE REMAINDER OF THE AREA.

&&

.FIRE WEATHER...
SEASONABLY VERY COLD TEMPERATURES AND MODERATE TO STRONG WEST
WIND WILL CONTINUE OVER MANY PORTIONS OF CENTRAL WYOMING TODAY AND
TONIGHT. THE WESTERLY FLOW WILL INCREASE TURBULENT MIXING AND THE
ASSOCIATED SMOKE DISPERSAL RATES IN THE MID AND HIGHER ELEVATIONS
THROUGH TONIGHT. THE FLOW WILL BECOME MORE SOUTHWESTERLY
FRIDAY...INCREASING WIND IN THE CODY AND LANDER FOOTHILLS AS WELL
AS THROUGH THE WIND CORRIDOR FROM JUST NORTHEAST OF ROCK SPRING TO
CASPER.

&&

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

$$

SHORT TERM...CHURCH
LONG TERM...AEM
AVIATION...TWB
FIRE WEATHER...CHURCH