FXUS65 KRIW 282211
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
311 PM MST SAT NOV 28 2009

.SHORT TERM...TONIGHT THROUGH TUESDAY
DEFORMATION AXIS CONTINUES TO SLIDE SOUTHEAST THROUGH THE REGION
THIS PM. JET ENERGY IS LEAVING THE AREA AS WELL...SO THE PRECIP
IS WINDING DOWN NOW. SOME ACCUMULATING SNOW...LESS THAN AN INCH...
DID OCCUR IN THE NORTH AND CENTRAL ZONES THIS MORNING AND AFTERNOON.
CLEARING SKY OVER THE NORTH...WEST AND SOUTH THIS PM WITH LOW
CLOUDS IN THE CENTRAL AND EAST CENTRAL ZONES. THE PRECIP SHOULD BE
ENDING BY 00Z IN MOST LOCATIONS WITH THE LOW CLOUDS BREAKING UP
BY 06Z IN THE CENTRAL ZONES. CONCERN ABOUT LOW CLOUDS AND FLURRIES
IN SWEETWATER COUNTY THIS EVENING AS LOW LEVEL MOISTURE PUSHES
INTO THAT AREA. WILL KEEP THE BULK OF THE CLOUDS THERE THROUGH
07Z. OTHERWISE HIGH CLOUDS WILL SPILL INTO THE AREA FROM NORTH TO
SOUTH LATE TONIGHT AS CLOUDS EVIDENT ON SATELLITE LOOPS UPSTREAM.
COLD NIGHT WITH GOOD RADIATIONAL COOLING IN THE BASINS AND
VALLEYS. UPPER LEVEL RIDGE OVER THE WESTERN U.S. FOR SUNDAY AND
MONDAY. DRY NW FLOW FOR THE MOST PART. THERE MAY BE A FEW MOUNTAIN
TOP SNOW SHOWERS SUNDAY OVER THE NW MTS AND NORTHERN BIGHORN MTS
WITH WEAK UPGLIDE HINTED AT IN THE MODELS. WILL LEAVE ISOLD
MOUNTAIN TOP SNOW IN THE FORECAST FOR NOW AND LET NEXT SHIFT
CONSIDER REMOVAL. OTHERWISE DRY FORECAST INTO MONDAY NIGHT WITH
LIGHT WIND IN THE BASINS AND VALLEYS WHICH WILL HAVE IMPACT FOR
TEMPS SUN AND MON. STILL A VARIETY OF MODEL SOLUTIONS FOR TUESDAY
WITH RESPECT TO A COLD FRONT PASSAGE AND PRECIP CHANCES ALONG AND
BEHIND IT. THE 12Z NAM IS FAST WITH THE FRONT AND HAS SOME ENERGY
MOVING INTO WY WHICH WOULD SUPPORT PRECIP. THE 18Z NAM IS EVEN
SHARPER WITH ITS TROUGH ON TUE AND IS STILL FAST. THE
GFS/EC/CANADIAN MODELS HAVE A SIMILAR SOLUTION WITH THE COLD FRONT
MOVING INTO THE NORTH TUE MORNING AND INTO THE CENTRAL TOWARD LATE
AFTERNOON. THE TROUGH IS NOT DIGGING BACK TO THE WEST AS MUCH AS
THE NAM SOLUTION BUT THEY DO SHOW SOME PRECIP TUE EVENING INTO TUE
NIGHT FOR THE EAST AND POSSIBLY THE CENTRAL ZONES. HAVE MADE
LITTLE ADJUSTMENT TO THE TUE FORECAST WITH THE CHANCE OF PRECIP IN
THE NORTH THROUGH 00Z WED. WILL SEE HOW THE NEXT MODEL RUNS LOOK
FOR TIMING AND STRENGTH. MONDAY AND TUESDAY WILL BE BREEZY TO
WINDY IN THE WIND CORRIDOR FROM NEAR KRKS TO KCPR. ALSO SOME GUSTY
WIND OVER AND NEAR THE ABSAROKA MTS MON AND TUE. HIGH TEMPS TO
GRADUALLY WARM SUNDAY AND MONDAY. TUE HIGHS WILL BE TRICKY THIS
FAR OUT DUE TO FRONTAL TIMING. EXPECT MILD HIGHS AHEAD OF FRONT
WITH COOLER HIGHS OVER THE NORTH AS FRONT EXPECTED THERE BY MIDDAY.

.LONG TERM...TUESDAY NIGHT THROUGH SATURDAY
CHALLENGING MEDIUM RANGE FORECAST WITH MODELS STRUGGLING AS TO HOW
TO HANDLE THE DEVELOPING WEST COAST RIDGE. GFS CRASHES A
SIGNIFICANT AMOUNT OF ENERGY THROUGH THE RIDGE THURSDAY ALLOWING A
SHARP COLD FRONT TO MOVE THROUGH ON FRIDAY. THE ECMWF MAINTAINS
THE RIDGE UNTIL LATER FRIDAY BEFORE A SHORTWAVE CRASHES THROUGH
AND DROPS INTO THE GREAT BASIN ON SATURDAY. BOTH MODELS HAVE THE
TUESDAY NIGHT SHORTWAVE AND CANADIAN FRONT BUT THE EURO IS FURTHER
WEST WITH A BETTER CHANCE OF SNOW EAST OF THE DIVIDE. THE GEM IS
NOW SIDING MUCH CLOSER TO THE GFS AND HAS BACKED OFF ITS HIGH
LATITUDE RIDGE TO OUR WEST. NCEP FAVORS THE ECMWF BUT ITS A TOUGH
CALL. I COULD SEE EITHER ONE WORKING HARD BASED ON ANALYSIS OF THE
NRN HEMISPHERIC AND HOW THE SERIES OF SHORTWAVES ROTATING OFF
SIBERIA INTERACT AS THEY GET INTO THE ERN PACIFIC. FORECAST IS
LEANING TOWARDS THE ECMWF AS THAT IS CLOSER TO OUR CURRENT
FORECAST. WE WILL NEED TO LOOK AT THIS AGAIN TONIGHT AND TRY TO
PINPOINT IT A LITTLE BETTER. CURRENT 00Z ECMWF WOULD GIVE US SOME
LIGHT SNOW TUESDAY NIGHT INTO WEDNESDAY MORNING BUT THAT'S IT FOR
THE PERIOD. LEFT IN SOME SLIGHT MTN CHANCES THROUGH MUCH OF THE
PERIOD IN NW FLOW. TEMPERATURES WILL BE TRICKY DEPENDING ON HOW
STRONG THIS INITIAL TUESDAY COLD FRONT IS AND IF IT LAYS DOWN ANY
SNOW EAST OF THE DIVIDE.

&&

.AVIATION...
EXPECT FREQUENT MTN OBSCURATIONS ALONG THE EAST SLOPES OF THE WIND 
RIVER AND SOUTHERN ABSAROKA MTS THROUGH 02Z SUNDAY WITH IMPROVING 
CONDITIONS THEREAFTER.  AREAS OF IFR/MVFR CLOUD DECKS MAY LINGER 
VCNTY AND SOUTH OF A KCPR-KLND-KRKS LINE OVERNIGHT...ESPECIALLY 
ALONG THE NORTH SLOPE OF CASPER MOUNTAIN. WEST OF THE DIVIDE...VFR 
CONDITIONS WILL PREVAIL WITH LOCAL FREEZING FOG POSSIBLE LATE 
TONIGHT AND SUNDAY MORNING.

&&

.FIRE WEATHER...
DRY WEATHER WILL PREVAIL THROUGH MONDAY NIGHT OVER THE REGION AS
HIGH PRESSURE MOVES INTO THE AREA. BASIN AND VALLEY INVERSIONS
WILL OCCUR THE NEXT TWO DAYS DUE TO THE HIGH PRESSURE AND THUS 
LITTLE OR NO MIXING. SMOKE DISPERSION WILL BE POOR IN THE VALLEYS
AND BASINS SUNDAY AND MONDAY. BREEZY TO WINDY AREAS WILL OCCUR
MONDAY AFTERNOON IN SOUTH AND EAST CENTRAL ZONES WITH A LEE SIDE
TROUGH DEVELOPING. 

&&

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

&&

$$

SHORT TERM...AR
LONG TERM...SKRBAC
AVIATION...CHURCH
FIRE WEATHER...AR