000
FXUS65 KRIW 200910
AFDRIW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
210 AM MST THU NOV 20 2008
.SHORT TERM...TODAY THROUGH SATURDAY NIGHT
SHALLOW NORTHEAST/EAST UPSLOPE FLOW CONTINUES IN CENTRAL WYOMING EARLY
THIS MORNING. SCATTERED LIGHT DRIZZLE/MIST (IN AREAS THAT APPARENTLY
INTERSECT WITH THE LOW LYING STRATUS CLOUDS THE RESULT OF
SUPERCOOLED WATER DROPLETS) AND LIGHT SNOW ASSOCIATED WITH THE
UPSLOPE FLOW WILL GRADUALLY DIMINISH THIS MORNING BEFORE
INCREASING SOUTHWEST FLOW ALOFT SCOURS OUT ANY STRATUS DURING THE
AFTERNOON. THE INCREASING SOUTHWEST FLOW ALOFT IS DUE TO A FAST
MOVING PACIFIC SHORT-WAVE TROUGH THAT WILL IMPACT THE NORTHERN
MOUNTAINS TONIGHT. AS SURFACE LOW PRESSURE RAPIDLY DEEPENS IN THE
LEE OF THE MONTANA ROCKIES TONIGHT...SOUTHWEST WIND WILL INCREASE.
BUMPED UP WIND SPEEDS IN THE HIGHER TERRAIN OF THE NORTHWEST
MOUNTAINS TONIGHT AND FRIDAY MORNING AS A RESULT. THE ISENTROPIC
UPGLIDE AHEAD OF THIS TROUGH IS EXPECTED TO BE WEAK AND SHORT-
LIVED AS THE ASSOCIATED COLD FRONT RAPIDLY MOVES INTO WESTERN
WYOMING AROUND MIDNIGHT. A QUICK SHOT OF MODERATE TO LOCALLY HEAVY
SNOW ALONG AND JUST BEHIND THE FRONT IS ANTICIPATED AFTER
MIDNIGHT. 2 TO 4 INCHES OF SNOW ACCUMULATION IN THE HIGHER
MOUNTAINS...MAINLY ALONG WEST FACING SLOPE IS EXPECTED BY MIDDAY
FRIDAY. THE UPPER LEVEL TROUGH WILL MOVE RAPIDLY EASTWARD FRIDAY
AS A AN UPPER LEVEL RIDGE TRANSITIONS OVER THE REGION IN THIS
PROGRESSIVE PATTERN. THE NEXT PACIFIC TROUGH IS PROGGED TO STAY
MAINLY NORTH OF THE AREA ALONG THE MT- ALBERTA BORDER BUT THE
RELATIVELY MOIST WEST- SOUTHWEST FLOW AT H7 AND ABOVE EXPECTED TO
PRODUCE ISOLATED LIGHT SHOWERS IN THE NORTHWEST MOUNTAINS SATURDAY
NIGHT.
.LONG TERM...SUNDAY THROUGH THURSDAY
A PROGRESSIVE PACIFIC TROUGH WILL MOVE EAST OF THE AREA ON SUNDAY
WITH NORTHWEST FLOW OVER THE AREA. HIGH PRESSURE WILL BUILD INTO
THE WEST THROUGH THE DAY WITH DRY CONDITIONS EXPECTED. A HIGH
PRESSURE RIDGE ALOFT WILL RETURN TO THE AREA SUNDAY NIGHT THROUGH
TUESDAY WITH DRY CONDITIONS EXPECTED. LOWS MAY BE COOLER WITH LESS
CLOUD COVER AT NIGHT BUT GENERALLY WITH RISING HEIGHTS...MILD
TEMPERATURES SHOULD CONTINUE WITH HIGHS ABOVE TO MUCH ABOVE NORMAL
IN THE EAST. SOUTHWEST FLOW AHEAD OF A PACIFIC TROUGH WILL BRING
SOME MOISTURE AND LIFT INTO THE WEST TUESDAY NIGHT AND WEDNESDAY
WITH SOME SHOWERS DEVELOPING IN THE WESTERN MOUNTAINS. BREEZY TO
WINDY CONDITIONS AND MILD TEMPERATURES ARE EXPECTED EAST OF THE
CONTINENTAL DIVIDE. MODELS IN FAIR AGREEMENT THROUGH THE EXTENDED
UP THROUGH WEDNESDAY THEN DIVERGE WITH THE HANDLING OF A PACIFIC
TROUGH OVER THE WEST WEDNESDAY NIGHT AND THURSDAY. ECMWF CUTS OFF
LOW AND BUILDS RIDGE OVER WYOMING WHILE GFS BRINGS A TROUGH
THROUGH AND SPREADS PRECIPITATION OVER THE AREA. HAVE KEPT THE
THREAT OF PRECIPITATION IN THE MOUNTAINS AND WEST AT THIS TIME.
&&
.AVIATION...
WIDESPREAD MVFR WITH LOCAL IFR CIGS WILL GRADUALLY ERODE ACROSS
SOUTH AND CENTRAL WYOMING LATE THIS MORNING THROUGH EARLY
AFTERNOON...16Z-20Z. THESE LOW CIGS WILL LINGER LASTLY AGAINST THE
EAST SLOPES OF THE WIND RIVER MOUNTAINS IN THE VCNTY OF KLND AND
ALONG AND WEST OF HIGHWAY 189 IN VCNTY OF KBPI 19Z-22Z.
A PACIFIC STORM SYSTEM WILL SPREAD AREAS OF MVFR AND LOCAL IFR
CONDITIONS INTO THE NORTHWEST MOUNTAINS INCLUDING VCNTY KJAC 02Z-06Z
FRIDAY. GUSTY DOWNSLOPE WINDS WILL DEVELOP FROM VCNTY KCOD-KLND
06Z-12Z FRIDAY WITH AREAS OF LLWS.
&&
.FIRE WEATHER...
SOUTHWEST WIND WILL BE ON THE INCREASE THIS AFTERNOON AS A FAST
MOVING PACIFIC TROUGH APPROACHES THE AREA. SCATTERED TO NUMEROUS
SHOWERS ARE EXPECTED OVER THE NORTHERN MOUNTAINS LATE TONIGHT
ALONG AND BEHIND THE ASSOCIATED COLD FRONT. THIS SYSTEM WILL
QUICKLY MOVE EAST OF THE AREA BY FRIDAY AFTERNOON. THE NEXT PACIFIC
TROUGH WILL MOVE THROUGH NORTHERN MONTANA AND BRING ANOTHER PACIFIC
FRONT ALONG WITH ISOLATED LIGHT SNOW SHOWERS TO THE NORTHWEST
MOUNTAINS SATURDAY NIGHT. DRY CONDITIONS ARE EXPECTED SUNDAY INTO
EARLY NEXT WEEK.
&&
.RIW WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SHORT TERM...CHURCH
LONG TERM...C.BAKER
AVIATION...AEM
FIRE WEATHER...CHURCH
