FXUS65 KRIW 261016
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
316 AM MST THU NOV 26 2009

.SHORT TERM...TODAY THROUGH SATURDAY NIGHT
THE RIDGE AXIS WILL BE SHIFTING EAST ACROSS WYOMING TODAY. SURFACE
HIGH PRESSURE WILL REMAIN IN PLACE IN SOUTHWEST WY. THIS SET UP
WILL RESULT IN STRONG VALLEY AND BASIN INVERSIONS ALTHOUGH HIGH
TEMPS WILL NOT BE ESPECIALLY COLD TODAY EXCEPT PERHAPS THE FAR
WESTERN VALLEYS WHERE THE LEAST AMOUNT OF MIXING AND INVERSION
SCOURING OCCURRED WITH THE ALBERTA CLIPPER LAST TUESDAY NIGHT.
ALSO...LOW STRATUS AND FOG INITIATED BY SNOW COVER THERE WILL
DELAY ANY HEATING THERE TODAY. THE BIG HORN BASIN...WIND RIVER
BASIN AND THE UPPER GREEN RIVER BASIN ALL HAD STRONG ENOUGH WINDS
LAST TUESDAY TO MIX OUT THE PREVIOUS INVERSION IN PLACE BEFORE THE
PASSAGE OF THE CLIPPER BUT YET WERE TOO FAR FROM THE BRUNT OF THE
COLD AIR ADVECTION DIRECTLY IN THE WAKE OF THE CLIPPER TO GET
SIGNIFICANTLY REPLENISHED WITH ADDITIONAL COLD AIR. AS A
RESULT...TEMPERATURES WILL BE THE TRICKIEST ELEMENT IN THE
FORECAST TODAY WITH H7 TEMPS INCREASING ALL THE WAY UP TO 5C THIS
AFTERNOON ALONG ALONG WITH ANY REMAINING INVERSIONS STILL IN
PLACE. TEMPS SHOULD PUSH 60 IN CPR TODAY WITH TEMPS WELL UP INTO
THE 60S EXPECTED TODAY IN JOHNSON COUNTY. CURRENTLY IN BOTH CPR
AND BYG...TEMPS ARE WARMER UNDER CLEAR SKIES THAN THEY WERE WITH
PRECIP FALLING THIS SAME TIME LAST NIGHT. 50S WILL BE COMMON IN
THE CENTRAL BASINS AS WELL AS THE UPPER GREEN RIVER BASIN TODAY.
WESTERN SWEETWATER COUNTY INCLUDING RKS WILL REMAIN ON THE
RELATIVELY COOL SIDE WITH THE CLOSE PROXIMITY TO THE SURFACE HIGH
SO EXPECT 40S THERE. EXPECT HIGH IN THE 30S IN THE WESTERN
VALLEYS. ONE MORE NIGHT OF BASIN AND VALLEY INVERSIONS IS EXPECTED
TONIGHT AND FRIDAY MORNING. THE SURFACE PRESSURE GRADIENT BETWEEN
THE SFC HIGH OVER SW WY AND THE LEE SIDE TROUGH OVER EASTERN WY
WILL CAUSE SOUTHWEST WINDS TO BLOW FROM EASTERN SWEETWATER COUNTY
TO CPR WHERE SUFFICIENT MIXING WILL OCCUR. JOHNSON COUNTY WILL NOT
BLOW PER SAY BUT THERE IS NO INVERSION THERE TO BEGIN WITH.

THE NEXT UPSTREAM SHORTWAVE NOW OFF THE PACIFIC COAST AT AROUND 140W 
WILL BE TRACKING EAST WITH THE TROUGH AXIS LIKELY REACHING WYOMING 
BY SATURDAY. THE NAM/ECMWF SPLITS THIS LONG WAVE TROUGH WITH THE 
NORTHERN STREAM ENERGY REACHING WY. THESE MODELS INDICATE AT LEAST 
TWO NORTHERN STREAM SHORTWAVES WITH THE SECOND ONE WASHING OUT AND 
THE FIRST ONE PHASING WITH THE SOUTHERN STREAM SHORTWAVE. THE GFS 
ALSO SPLITS THE ENERGY AND PHASES THE SECOND NORTHERN STREAM 
SHORTWAVE WITH THE SOUTHERN STREAM SHORTWAVE. IN ANY EVENT...IT IS A 
SPLITTING SYSTEM SO WILL KEEP PRECIP AMOUNTS RELATIVELY LIGHT FOR 
NOW IN SPITE OF THE FACT THAT THERE IS AN EVIDENT PINEAPPLE 
CONNECTION WITH THIS FEATURE. WINDS ACROSS THE EAST SLOPE OF THE 
WIND RIVER MOUNTAINS AND THE ABSAROKA MTNS WILL RESPOND TO THE 
INCREASING GRADIENT TONIGHT AHEAD OF THIS APPROACHING SYSTEM WITH 
WEST SOUTHWEST WINDS OF 30 TO 40 MPH GUSTING TO 45 MPH. GUSTS TO AT 
LEAST 50 MPH ARE LIKELY ACROSS THE NORTHERN ABSAROKA MTNS NEAR CLARK 
WHERE THE WRF INDICATES 50KT SURFACE WIND SPEEDS AND THE ARW4 40 
KNOT WINDS. WITH INCREASING WINDS ACROSS THE AREA 
FRIDAY...INVERSIONS WILL LIKELY COMPLETELY SCOUR OUT WITH BASINS AND 
VALLEYS EXPERIENCING THEIR WARMEST DAY OF THE WEEK. ON THE OTHER 
HAND...OTHER AREAS LIKE CPR AND BYG WILL COOL DOWN SOMEWHAT WITH 
COOL AIR ADVECTION BEGINNING TO TAKE PLACE FRIDAY ALONG WITH SOME 
INCREASE IN CLOUDS...ALTHOUGH THESE AREAS SHOULD STILL REMAIN THE 
WARMEST LOCATIONS FRIDAY. 

.LONG TERM...SUNDAY THROUGH THURSDAY
IN WAKE OF THE TROUGH ON SATURDAY...A RIDGE IS EXPECTED 
TO BUILD INTO THE AREA SUNDAY AND MONDAY...WITH DRY CONDITIONS AND A 
WARMING TREND...ESPECIALLY ON MONDAY.  HOWEVER...THIS WILL BE SHORT 
LIVED AS MEDIUM RANGE MODELS ARE IN GOOD AGREEMENT IN DIVING A 
TROUGH OUT OF THE GULF OF ALASKA SUNDAY...INTO THE NORTHERN ROCKIES 
MONDAY NIGHT AND TUESDAY.  THE ECMWF/GEM/UKMET CONTINUE TO SHOW MORE 
ENERGY ON THE BACKSIDE OF THIS TROUGH TUESDAY...THAN THE PAST 
SEVERAL RUNS OF THE GFS.  THIS WOULD RESULT IN COOLER CONDITIONS AND 
MORE INCLEMENT WEATHER THAN THE GFS/MEX MOS IS CURRENTLY 
INDICATING.  HAVE TRENDED COOLER TUESDAY THROUGH THURSDAY...AND 
BROAD BRUSHED MAINLY LOW POPS FOR NOW FOR THAT TIMEFRAME...WITH THE 
HIGHEST POPS TUESDAY/TUESDAY NIGHT WITH THE INITIAL TROUGH.  WILL 
NEED TO GO CONSIDERABLE COOLER WEDNESDAY AND THURSDAY IF THE ECMWF 
ENDS UP VERIFYING AS IT HAS 700MB TEMPS ABOUT 10 DEGREES CELSIUS 
COLDER THAN THE GFS. 

&&

.AVIATION...
KJAC TO REMAIN THE TROUBLE SPOT THROUGH AT LEAST MID MORNING 
THANKSGIVING DAY...IF NOT ABOUT 19Z/WED. LATE EVENING SATELLITE FOG 
IMAGE INDICATING SOME LOW CLOUDS FORMING AT THE NORTH END OF THE 
JACKSON VALLEY. EXPECT HIGH BOUNDARY LAYER MOISTURE TO AGAIN ALLOW 
FOR KJAC TO SEE IFR/MVFR CONDITIONS. WITH THIS SET-UP...TOUGH TO 
DETERMINE CEILING HEIGHT AND PERSISTENCE OF THESE CLOUDS DURING THE 
MORNING. EITHER WAY...WILL EXPECT VFR CONDITIONS BY 19Z/WED THROUGH 
THE FORECAST PERIOD. ELSEWHERE...VFR CONDITIONS WILL PREVAIL AT ALL 
OTHER TERMINALS. LEE TROUGH OVER EASTERN WYOMING WILL ALLOW FOR 
GUSTY SOUTHWEST SURFACE WIND OF 20 TO NEAR 35KTS AT KCPR THROUGHOUT 
THANKSGIVING. LESSER WEST-SOUTHWEST WIND OF 10-15KTS AT KRKS WHILE 
OTHER LOCATIONS WILL BE GENERALLY LESS THAN 8KTS.

&&

.FIRE WEATHER...
DRY WEATHER WITH BASIN AND VALLEY INVERSIONS WILL 
FEATURE THE WEATHER TODAY. UNSEASONABLY MILD WEATHER WILL OCCUR FROM 
EASTERN SWEETWATER COUNTY TO JOHNSON COUNTY THIS AFTERNOON. EXPECT 
INCREASING SOUTHWEST WINDS FROM THE RED DESERT TO CASPER TODAY. WEST 
WINDS WILL BLOW FROM 30 TO 40 MPH WITH GUSTS TO 50 MPH ACROSS THE 
EASTERN WIND RIVER AND ABSAROKA MOUNTAINS TONIGHT AS THE PRESSURE 
GRADIENT INCREASES AHEAD OF AN APPROACHING PACIFIC WEATHER SYSTEM. 
MILD WEATHER WILL CONTINUE FRIDAY WITH INVERSIONS SCOURING OUT. THE 
AFOREMENTIONED WEATHER FEATURE WILL PRODUCE UP TO 3 TO 6 INCHES OF 
SNOWFALL FOR THE WESTERN MOUNTAINS AND 1 TO 3 INCHES IS EXPECTED IN 
THE WESTERN VALLEYS...MAINLY ON SATURDAY. SOME OF THIS PRECIPITATION 
MAY SPILL OVER TO AREAS EAST OF THE DIVIDE SATURDAY AFTERNOON IN THE 
FORM OF LIGHT RAIN AND SNOW. EXPECT PARTIAL CLEARING SATURDAY NIGHT.

&&

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

$$

SHORT TERM...LIPSON
LONG TERM...WM
AVIATION...CNJ
FIRE WEATHER...LIPSON