000
FXUS65 KRIW 162136
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
236 PM MST MON FEB 16 2009

.SHORT TERM...TONIGHT THROUGH THURSDAY
COMPLEX SCENARIO SETTING UP FOR THE NEXT 36 TO 48 HOURS WITH
COMBINATION OF NEWD MOVING SHORTWAVE...UPPER LOW AND SWD MOVING
ARCTIC CLIPPER. MODELS ARE NOT AS AGGRESSIVE EAST OF THE DIVIDE AS
YESTERDAY...ESPECIALLY ON WEDNESDAY. SOME OF THAT IS DUE TO A
FASTER SWD MOVEMENT WITH THE ARCTIC WAVE AND PART OF IT IS THE
MODELS SHOWING A WEAKER REMNANT UPPER LOW MOVING FROM ERN IDAHO TO
CENTRAL WYO. THE END RESULT FOR THE SENSIBLE WEATHER MAY NOT BE
ALL THAT DIFFERENT BUT THE SNOWFALL AMOUNTS ARE STILL A CHALLENGE.
IT STILL LOOKS LIKE THE SHORTWAVE THAT SHOOTS OUT THE BOTTOM OF THE
OFFSHORE CA LOW WILL MOVE NE INTO SWRN WY THIS EVENING AND ACROSS
ALL OF THE WEST BY AROUND MIDNIGHT. REMNANT UPPER LOW WILL TRACK
FROM THE TETONS TO THE WIND RIVER BASIN TUESDAY MORNING WITH
CONVERGENCE AXIS ALONG ITS TRACK AS SWD MOVING FRONT INTERACTS
WITH IT TUESDAY AFTERNOON. STEEP LAPSE RATES AND LOW LIFTED
INDICES MAY LEAD TO LATE AFTERNOON CONVECTION FORMING OVER THE
SERN ABSAROKAS AND OWL CREEKS MOVING SE ACROSS THE WIND RIVER
BASIN. THE LANDER FOOTHILLS MAY ALSO SEE SOME SNOW OR MIXED RAIN
AND SNOW SHOWERS LATE IN THE DAY. STILL NOT CLEAR CUT ON THE EXACT
SCENARIO BUT HAVE CONTINUED TRENDS OF HIGHER POPS IN THE AREA.
OTHERWISE...SNOW WILL CONTINUE OUT WEST WITH POSSIBLE HIGHLIGHTS
NEEDED ANYWHERE FROM THE TETONS SWD EARLY TUESDAY INTO EARLY
WEDNESDAY. SINCE MOST OF THE SNOW WILL BE TUESDAY AND TUESDAY
NIGHT...WILL LET THE NEXT CREW GIVE IT ONE MORE LOOK BEFORE
ISSUING ANY POSSIBLE HIGHLIGHTS. BEST SNOW IN THE TETONS SHOULD BE
FROM AROUND MIDDAY TUESDAY INTO EARLY WEDNESDAY WHEN W TO NW FLOW
DEVELOPS. SWD MOVING ARCTIC WAVE WILL AFFECT THE N AND E LATE
TUESDAY NIGHT INTO WEDNESDAY WITH COLDER AIR AND LIGHT SNOW. STILL
SOME QUESTION ON HOW AND IF THE LEFT OVER DEFORMATION AXIS WILL
INTERACT WITH THE COLD FRONT ON WEDNESDAY. MODELS HAVE BACKED AWAY
FROM THIS IDEA SINCE YESTERDAY BUT I STILL THINK THERE IS SOME
POTENTIAL AND THIS WILL HAVE TO BE WATCHED FOR OUR ERN ZONES. SOME
LIGHT SNOW OR FLURRIES MAY LINGER IN THE WEST INTO WEDNESDAY NIGHT
BEFORE ENDING OR RETREATING TO THE HIGHEST NWRN PEAKS.
TEMPERATURES WILL STILL BE TRICKY AROUND THE CENTRAL ZONES AHEAD
OF THE FRONT WHERE WARMER MID LEVEL TEMPS PERSIST BUT ARE BALANCED
SOME BY INCREASING CLOUD COVER. BUMPED TEMPS UP A COUPLE DEGREES
BASED ON HOW EASILY WE CRACKED 40 TODAY AND WARMER MID LEVEL TEMPS
THAT REMAIN THROUGH MIDDAY TUESDAY. OTHERWISE...IT SHOULD BE QUITE
A BIT COOLER IN THE ERN ZONES ON WEDNESDAY WITH H7 TEMPS OF -11 TO
-12...CLOUDS AND PERIODS OF LIGHT SNOW...ESPECIALLY IN THE
MORNING. INVERSIONS BEGIN TO RETURN ON THURSDAY WITH SW BREEZES
RETURNING TO THE WIND CORRIDOR.

.LONG TERM...THURSDAY NIGHT THROUGH MONDAY
A WEAK SHORTWAVE IN NW FLOW APPROACHES NRN WY LATE THURSDAY AND
PASSES THROUGH THURS NIGHT. WILL KEEP LOW PRECIP CHANCES IN THE
MTS OF THE NORTH. NORTHERN JOHNSON COUNTY MAY SEE LIGHT DUSTING OF
SNOW THURS NIGHT. FRIDAY SEEMS DRY AS UPPER RIDGE AXIS TO THE WEST
AMPLIFIES. HAVE LOWERED PRECIP CHANCES IN THE MTS TO SLIGHT CHANCE
AND MAY GO DRY IF MODELS CONTINUE TO SHOW LACK OF MOISTURE FRI.
UPPER RIDGE OVER THE AREA FRIDAY NIGHT AND SATURDAY WITH DRY
WEATHER EXPECTED. SAT NIGHT LOOKS DRY ASIDE FROM A FEW SNOW
SHOWERS DEVELOPING LATE SAT NIGHT IN THE WRN MTS. THIS TIMING MAY
BE TOO FAST AND WILL SEE HOW THINGS LOOK TONIGHT. GFS AND ECMWF
MODELS SIMILAR WITH NEXT TROUGH NEXT SUNDAY INTO MONDAY. PRECIP
CHANCES TO INCREASE IN WRN WY SUN AFTERNOON WITH BETTER CHANCE OF
PRECIP SUN NIGHT THROUGH MONDAY NIGHT. WILL WATCH THIS OVER THE
NEXT FEW NIGHTS AND ADJUST FORECAST AS NEEDED. AS FOR TEMPS...
SEASONAL TO ABOVE NORMAL HIGHS AND LOWS THROUGH THE WEEKEND WITH
SOME COOLING FOR NEXT MONDAY DUE TO PRECIP AND COLDER AIR WITH
TROUGH.

&&

.AVIATION...
A WEAKENING TROUGH OF LOW PRESSURE WILL BE TRACKING EAST NORTHEAST
TO THE CENTRAL ROCKIES TONIGHT. THIS WEATHER FEATURE WILL SPREAD
LIGHT SNOWFALL AND LOWERING CIGS INTO FAR WESTERN WYOMING AND THE
UPPER GREEN RIVER BASIN TONIGHT. EXPECT MVFR CONDITIONS TO DEVELOP
IN THESE AREAS TONIGHT LOWERING TO IFR BY SUNRISE TUESDAY. MVFR
CONDITIONS WILL DEVELOP OVER SWEETWATER COUNTY INCLUDING KRKS BY 09Z
TONIGHT WITH CONDITIONS BECOMING IFR BY 17Z. CONDITIONS WILL IMPROVE
TO MVFR OVER KPNA AND KBPI EXCEPT WILL REMAIN IFR...OCCASIONALLY LIFR
OVER THE FAR WEST INCLUDING KJAC WHERE A MOIST WESTERLY UPSLOPE FLOW
WILL PROLONG THE HEAVIER SNOW THERE. IN THE MEANTIME A SURFACE COLD
FRONT WILL BE SHIFTING THE WINDS TO THE NORTH ACROSS THE NORTHERN
BIG HORN BASIN AND JOHNSON COUNTY AROUND 18Z TUESDAY. AS THIS FRONT
TRACKS SOUTH...MVFR CONDITIONS ARE EXPECTED TO DEVELOP AT KCOD BY
19Z WITH THESE CONDITIONS SPREADING SOUTH TO KCPR BY 22Z.
KWRL...KRIW AND KLND WILL HAVE MAINLY VFR CONDITIONS THROUGH TUESDAY.

&&

.FIRE WEATHER...
A STORM SYSTEM WILL SPREAD SNOW INTO THE SOUTHWEST PART OF THE
DISTRICT THIS EVENING AND SPREAD THROUGHOUT THE REST OF THE WEST
BY MIDNIGHT. ON TUESDAY...WIDESPREAD SNOW IS EXPECTED IN THE WEST
WITH THE CHANCE OF RAIN OR RAIN AND SNOW MIXTURE INCREASING EAST
OF THE DIVIDE. A COLD FRONT WILL SHIFT WINDS TO THE NORTH ACROSS
THE NORTHERN PART OF THE DISTRICT TUESDAY MORNING WITH GUSTY WEST
WINDS TO THE SOUTH REMAINING. ANOTHER COLD FRONT WILL PUSH SOUTH
TUESDAY NIGHT INTO WEDNESDAY WITH ANOTHER INCREASED CHANCE OF SNOW
FROM BUFFALO TO CASPER.

&&

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

&&

$$

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