FXUS65 KRIW 262255
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
355 PM MST THU NOV 26 2009

.SHORT TERM...TONIGHT THROUGH SUNDAY
UPPER LEVEL RIDGE AXIS WILL SHIFT EAST OF CENTRAL WYOMING TONIGHT
WITH FLOW SWITCHING TO THE SOUTHWEST AND INCREASING THROUGH THE NIGHT.
LEE CLOUDS WAVE DEVELOPED OVER THE NORTH AND CENTRAL AREAS WITH
CONVECTIVE CLOUDS DEVELOPING IN EASTERN IDAHO MOVING TOWARDS THE
WESTERN MOUNTAINS, CLOUD COVER AND INCREASED WIND WILL MODERATE
LOW TEMPERATURES AND WARMING IN THE LEE OF THE MOUNTAINS WILL
CONTINUE. FRIDAY WILL SEE INCREASING CLOUDS THROUGH THE DAY FRIDAY.
THE CLOUD INCREASE WILL KEEP TEMPERATURES FROM MORE SIGNIFICANT IN
THE WEST. STRONG WINDS WILL BLOW IN AND NEAR THE EAST SLOPES OF
THE MOUNTAINS AND THROUGH THE WIND CORRIDOR FROM ROCK SPRINGS TO
CASPER. THE STRONGEST WINDS ARE EXPECTED IN THE CLARK AREA NORTH
OF CODY. SHOWERS WILL DEVELOP IN THE NORTHWEST LATE IN THE
AFTERNOON AND THE SPREAD SOUTH AND EAST THROUGH THE NIGHT FRIDAY.
THE TROUGH WILL BRING A COLD FRONT THROUGH THE WEST FRIDAY NIGHT
MOVING IN THE NORTH SATURDAY AND SPREADING SOUTH THROUGH THE DAY
EAST OF THE CONTINENTAL DIVIDE. MOISTURE WILL BE LIMITED IN THE
EAST WITH AREAS OF LIGHT SNOW DEVELOPING. THE WESTERN MOUNTAINS
SHOULD PICK UP 2 TO 4 INCHES OF SNOW WITH 1 TO 2 IN THE VALLEYS.
SATURDAY AND SATURDAY NIGHT LOCAL AREAS AROUND AN INCH ARE
EXPECTED IN JOHNSON AND NATRONA COUNTIES. HIGH PRESSURE WILL BUILD
BACK IN ON SUNDAY WITH COOLER TEMPERATURES BEHIND THE COLD FRONT
BUT MORE SUN AS CLOUDS DECREASE.

.LONG TERM...SUNDAY NIGHT 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...

LARGE RIDGE OVER THE ROCKY MOUNTAINS WILL SLOWLY SHIFT TO THE EAST 
TONIGHT AND FRIDAY. FEW TO SCATTERED HIGH CLOUD WILL SPILL EASTWARD 
THROUGH THE RIDGE AXIS TONIGHT AND FRIDAY WITH VFR CONDITIONS 
EXPECTED THROUGH THE PERIOD. STRONG WESTERLY FLOW ALONG THE CREST OF 
THE UPPER RIDGE TONIGHT AND FRIDAY WILL GENERATE A LEE SURFACE 
TROUGH ACROSS THE WESTERN PLAINS. THIS AREA OF LOW PRESSURE TO THE 
EAST WILL CAUSE WEST WINDS AROUND 10 KT TO DEVELOP AT KCOD AFTER 06Z 
TONIGHT THROUGH FRIDAY AND WIND GUSTS UP TO 25 KT TONIGHT AND UP TO 
35 KT FRIDAY AT KCPR. WINDS BE BE LIGHT AND VARIABLE ACROSS THE REST 
OF CENTRAL AND WESTERN WYOMING TONIGHT AND FRIDAY. 

&&

.FIRE WEATHER...

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. IN THE WEST CLOUDS WILL INCREASE AHEAD OF A PACIFIC
TROUGH WHICH WILL PRODUCE UP TO 2 TO 4 INCHES OF SNOWFALL FOR THE
WESTERN MOUNTAINS AND 1 TO 2 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...C.BAKER
LONG TERM...WM
AVIATION...SMITH
FIRE WEATHER...C.BAKER