FXUS65 KRIW 292301
AFDRIW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
401 PM MST SUN NOV 29 2009
.SHORT TERM...TONIGHT THROUGH WEDNESDAY
AREAS OF FOG AND LOW CLOUDS FINALLY BROKE BY 20Z IN THE WIND
RIVER BASIN AND THE FAR NORTHERN BIG HORN BASIN. OTHERWISE ONLY
HIGH CLOUDS OVER THE AREA THIS AFTERNOON. PARTLY CLOUDY TO MOSTLY
CLEAR TONIGHT WITH HIGH CLOUDS MOVING THROUGH THE REGION. LARGE
SPREAD ON LOW TEMPS TONIGHT AS THE VALLEYS WILL RADIATE WELL WITH
MILDER READINGS IN THE HIGH COUNTRY AND THE MIXED LOCATIONS. UPPER
RIDGE TO MOVE OVER THE AREA MONDAY WITH DRY WEATHER. LEE SIDE
TROUGH WILL FORM WITH WINDY CONDITIONS IN THE SOUTH AND EAST CENTRAL
ZONES AS A RESULT MONDAY INTO MONDAY NIGHT. WINDY WEATHER WILL
ALSO OCCUR OVER THE ABSAROKA MTS AS WELL MONDAY INTO MONDAY NIGHT.
A WEATHER SYSTEM WILL MOVE INTO WY ON TUESDAY AND TUESDAY NIGHT.
THE NAM HAS CONTINUED TO POINT TO A STRONGER COLD FRONT WITH A
GOOD POTENTIAL FOR PRECIP WITH THE SYSTEM. THE 18Z NAM/18Z GFS
AND 12Z ECWMF MODELS ARE NOW POINTING TO A COLDER SYSTEM WITH A
BETTER CHANCE OF PRECIP AND CERTAINLY LOW CLOUDS BEHIND THE FRONT.
CURRENT FORECAST HAS PRECIP IN THE FAVORED LOCATIONS AND I HAVE
INCREASED PRECIP CHANCES A LITTLE MORE AS MODELS SEEM TO BE COMING
IN LINE WITH A STRONGER SYSTEM. I HAVE COOLED LOW TEMPS A BIT MORE
TUE NIGHT AND LOWERED HIGHS ON WED. A BRISK NORTH WIND SHOULD
OCCUR POST FRONT AND AREAS OF LIGHT SNOW SHOULD OCCUR EAST OF THE
DIVIDE WITH THE BEST CHANCE IN THE UPSLOPE FAVORED LOCATIONS.
.LONG TERM...WEDNESDAY NIGHT THROUGH SUNDAY
DIFFICULT MEDIUM RANGE FORECAST WITH WIDELY VARYING MODEL SOLUTIONS
AND NO CLEAR CUT CONSENSUS. MAIN FORECAST PROBLEM IS WHETHER RIDGE
WILL HOLD OVER THE WRN U.S. OR WILL A STRONG SHORTWAVE CRASH THROUGH
IT WHILE THE RIDGE REDEVELOPS FURTHER WEST. THE 00Z GFS CONTINUES TO
SUPPORT A SIGNIFICANT SHORTWAVE MOVING THROUGH THE RIDGE THURSDAY
WITH THE GEM AND UKMET BEING ABOUT A 12-18 HOURS SLOWER ON THIS
IDEA. THE 00Z ECMWF MAINTAINS THE RIDGE INTO THE WEEKEND. NCEP
PREFERRED THE GFS IDEA IN THE PMDEPD BUT OVERNIGHT DISCUSSIONS
FAVORED THE ECMWF. AFTER COLLABORATION WITH OUR NEIGHBORS...WE
GENERALLY LEFT THE FORECAST UNCHANGED WHICH GENERALLY FOLLOWS THE
ECMWF SOLUTION. CONFIDENCE IS LOW WITH RAPID CHANGES AND FAST FLOW
ACROSS THE PACIFIC. SEVERAL LARGE PIECES OF THE SIBERIAN COLD POOL
BREAK OFF AND TRAVEL ACROSS THE PACIFIC WITH THE POTENTIAL FOR A
LARGE UPPER LOW OVER THE CENTRAL PACIFIC WHICH COULD REDEVELOP THE
UPPER RIDGE FARTHER WEST SUPPORTING THE GFS/GEMS/UKMET IDEA BUT
ITS A TOUGH CALL. WILL LOOK AT THE HEMISPHERIC PATTERN AGAIN
TONIGHT AND SEE IF WE CAN COME UP WITH THE BEST SOLUTION AND
ADJUST AS NECESSARY. THE GFS IS OBVIOUSLY MUCH COLDER FRIDAY AND
SATURDAY WITH H7 TEMPS OF -16C TO -20C WHILE THE ECMWF IS MORE IN
THE -3C TO -8C RANGE. AND OF COURSE...RIDGE CRASHING MODELS WOULD
SUPPORT SOME LIGHT SNOW IN AT LEAST THE NRN HALF FRIDAY INTO
SATURDAY WHILE THE EURO WOULD NOT.
&&
.AVIATION...
VFR CONDITIONS WILL PREVAIL TONIGHT AND MONDAY MORNING UNDER A
STRONG RIDGE OF HIGH PRESSURE ALOFT. LOCAL IFR/LIFR FREEZING FOG
WILL OBSCURE TERRAIN IN THE BIG HORN BASIN VCNTY KGEY/KWRL...THE
WIND RIVER BASIN VCNTY KRIW/KLND TONIGHT THROUGH 18Z MONDAY. AS
SURFACE PRESSURES FALL IN THE LEE OF THE NORTHERN ROCKIES TONIGHT
SOUTHWEST WIND WILL INCREASE TO THE 12-20KT RANGE AFTER 06Z
MONDAY IN THE WIND CORRIDOR FROM JUST NORTHEAST OF KRKS TO KCPR.
&&
.FIRE WEATHER...
DRY WEATHER THROUGH MONDAY NIGHT. BREEZY TO WINDY AREAS WILL OCCUR
OVER THE SOUTH AND EAST CENTRAL AS WELL AS IN THE ABSAROKA
MOUNTAINS MONDAY INTO MONDAY NIGHT. BASIN INVERSIONS WILL OCCUR
MONDAY WITH LIGHT WIND AND POOR SMOKE DISPERSAL. A WEATHER SYSTEM
WILL BRING A CHANCE OF SNOW TO THE NORTH AND CENTRAL ZONES TUESDAY
AND TUESDAY NIGHT.
&&
.RIW WATCHES/WARNINGS/ADVISORIES...NONE.
&&
$$
SHORT TERM...AR
LONG TERM...SKRBAC
AVIATION...SKRBAC
FIRE WEATHER...AR
