FXUS65 KRIW 280917
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
217 AM MST SAT NOV 28 2009

.SHORT TERM...TODAY THROUGH MONDAY NIGHT
TROUGH SPLITTING AS EXPECTED WITH THE SOUTHERN PIECE DIGGING SOUTH 
THROUGH CALIFORNIA.  THE NORTHERN PORTION IS SWINGING ACROSS SOUTHERN 
CANADA.  A SECONDARY SHORTWAVE MOVING INTO THE WEST CENTRAL ALBERTA 
AS WELL.  COLD FRONT MOVING THROUGH NORTHERN WYOMING EARLY THIS 
MORNING WITH SOME PATCHY LIGHT RAIN/SNOW FALLING OVER SOUTH CENTRAL 
MONTANA. VERY LIGHT REFLECTIVITIES SHOWING UP OVER THE TETONS AND 
SOUTHWEST YELLOWSTONE PER KSFX RADAR.  

THE TROUGH WILL CONTINUE TO SPLIT TODAY WITH THE DEFORMATION AXIS 
SLIDING SOUTH AND EAST ACROSS WYOMING.  THE SURFACE COLD FRONT WILL 
PUSH SOUTH THROUGH WYOMING BY LATE THIS MORNING WITH A NORTH TO 
NORTHEAST UPSLOPE FLOW DEVELOPING.  SOME AREAS OF LIGHT SNOW WILL MOVE INTO 
THE NORTH AND CENTRAL THIS MORNING AS THE DEFORMATION AXIS MOVES 
THROUGH.  EXPECT TRACE AMOUNTS AT BEST MAINLY IN THE MOUNTAINS.  
OTHERWISE EXPECT LOW CLOUDS TO MOVE BE AROUND FOR MUCH OF THE 
DAY...BREAKING OUT LATE IN THE AFTERNOON/EVENING.  COLDER AIR MOVES 
IN BEHIND THE TROUGH WITH H7 TEMPS OF -10C TO BE FOUND ACROSS THE 
NORTH.  RIDGE BUILDS IN OVERNIGHT TONIGHT WITH DECENT CLEARING 
TAKING PLACE.  WEAK WARM AIR ADVECTION WILL BE OVER THE AREA AS 
WELL.  THIS WILL ALLOW FOR GOOD RADIATIONAL COOLING WITH SOME OF THE 
WESTERN BASINS APPROACHING ZERO FOR MIN TEMPS SUNDAY MORNING.  
NORTHWEST TO NORTH FLOW REMAINS OVER WYOMING SUNDAY WITH MINIMAL 
MOISTURE SPILLING OVER THE RIDGE.  SOME WEAK ISENTROPIC LIFT LOOKS 
TO BRING A SLIGHT CHANCE OF LIGHT SNOW OR FLURRIES TO THE ABSAROKAS 
AND BIGHORNS.  FLOW SLOWLY BACKS TOWARDS THE WEST MONDAY AS RIDGE 
FLATTENS AS THE NEXT TROUGH APPROACHES THE PACIFIC CANADIAN COAST.  
TEMPERATURES ALOFT WARM MONDAY AS WELL WITH TEMPERATURES REBOUNDING 
INTO THE 40S...30S WEST.  LEE TROUGH STRENGTHENS IN RESPONSE TO THE 
APPROACHING TROUGH.  WINDS WILL LIKELY GET QUITE WINDY MONDAY 
AFTERNOON AND NIGHT OVER THE CENTRAL WIND CORRIDOR AS WELL AS ALONG 
THE EAST SLOPES OF THE ABSAROKAS AND WIND RIVERS.  

.LONG TERM...TUESDAY 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...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...

A COLD FRONT WILL BRING SCT MVFR/IFR CIGS WITH PRIMARILY MVFR VSBY 
IN -SN ALONG AND EAST OF THE DIVIDE TODAY WITH THESE CONDITIONS MORE 
ISOLATED WEST OF THE DIVIDE.  EXPECT FQT MTN OBSCURATIONS ALONG THE 
EAST SLOPES OF THE WIND RIVER AND ABSAROKA MTS AS WELL AS OVER THE 
BIG HORN MOUNTAINS THROUGH 21Z WITH IMPROVING CONDITIONS 
AFTERWARDS.  AREAS OF IFR/MVFR CLOUD DECKS MAY LINGER VCNTY AND 
SOUTH OF A KCPR-KLND-KRKS LINE OVERNIGHT SATURDAY...ESPECIALLY OVER 
THE SOUTH PASS AREA.

&&

.FIRE WEATHER...

A TROUGH WILL MOVE ACROSS THE STATE TODAY BRINGING A COLD FRONT 
THROUGH THIS MORNING.  SOME LIGHT SNOW IS POSSIBLE OVER THE NORTHERN 
TWO THIRDS OF THE STATE...WITH LITTLE IF ANY ACCUMULATIONS 
EXPECTED.  IT WILL BE COOLER TODAY WITH MORE HUMIDITY AROUND EAST OF 
THE DIVIDE.  IT WILL DRY OUT SUNDAY AND MONDAY WITH THE NEXT TROUGH 
APPROACHING TUESDAY INTO WEDNESDAY.  WINDS WILL INCREASE IN THE 
USUAL SPOTS MONDAY AFTERNOON AND NIGHT.  SMOKE DISPERSAL WILL BE 
POOR MOST AREAS THROUGH MONDAY AFTERNOON...IMPROVING IN THE WINDY 
AREAS.

&&

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

&&

$$

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