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000
FXUS65 KRIW 300530
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1030 PM MST FRI NOV 29 2013

.SHORT TERM...TONIGHT THROUGH SATURDAY (ISSUED AT 346 PM MST)

A NORTHEAST SOUTHWEST ORIENTED BAND OF HIGH AND MID CLOUDS EXTENDING
FROM WESTERN MONTANA...ACROSS NORTHERN IDAHO AND INTO NORTHERN
OREGON WILL HEAD FOR WYOMING DURING THE COURSE OF THE NIGHT TONIGHT.
CLOUDS WILL INCREASE IN THE CWA LATER THIS EVENING ALONG WITH
LOWERING CLOUDS IN THE WEST WITH SNOW FLURRIES DEVELOPING IN THE
NORTHWEST MTNS. THESE CLOUDS AND FLURRIES WILL BE ASSOCIATED WITH A
WEAK VORT LOBE THAT WILL TRACK SOUTHEAST ACROSS THE AREA LATE
TONIGHT. A SLIGHTLY MORE PROMINENT SHORTWAVE WILL TRACK TOWARD
WYOMING SATURDAY AND SATURDAY NIGHT WITH FLURRIES BECOMING AREAS OF
PATCHY AREAS OF LIGHT SNOW SATURDAY AS THIS WEATHER FEATURE
APPROACHES. IN THE MEANTIME...RATHER DRY AND BENIGN WEATHER IS
EXPECTED ACROSS AREAS EAST OF THE DIVIDE AS WELL AS OVER SWEETWATER
COUNTY. SOUTHWEST WINDS OF 10 TO 25 MPH FROM RKS TO CPR IS EXPECTED
REFLECTING THE UNIMPRESSIVE 11MB SURFACE PRESSURE GRADIENT FROM GCC
TO RKS. TEMPS WILL BE ON THE MILD SIDE WITH ONE MORE STRONG SHALLOW
NIGHTTIME AND MORNING TEMPERATURE INVERSION EXPECTED TONIGHT AND
SATURDAY MORNING.

.LONG TERM...SATURDAY NIGHT THROUGH MONDAY

APPROACHING SHORTWAVE SATURDAY EVENING WILL BE THE HARBINGER OF A
MAJOR CHANGE OUT WEST. LIGHT SNOW OR FLURRIES WILL BECOME MORE
LIKELY AS THE NIGHT WEARS OUT WEST...ESPECIALLY THE NW MOUNTAINS.
BEHIND THIS SHORTWAVE...A QUICKLY DEVELOPING ISENTROPIC UPGLIDE
PATTERN DEVELOPS AND INCREASES AS THE NW FLOW STRENGTHENS. THIS
MOIST UPGLIDE PATTERN WILL LIKELY RESULT IN INCREASING SNOWFALL
RATES IN THE NW SUNDAY AFTERNOON...QUICKLY SPREADING SOUTH THROUGH
ALL OF THE FAR WEST. IT LOOKS LIKE IT WILL BE COLD ENOUGH FOR THE
PCPN TO START AS SNOW IN THE WESTERN VALLEYS SO I LOWERED HIGHS
AND MADE SURE THE WEATHER SAID SNOW FOR THE JACKSON AND STAR
VALLEYS. WINDS WILL ALSO BE ON THE INCREASE AS THE FLOW
STRENGTHENS AND 100-120KT JET APPROACHES LEADING TO BLOWING AND
DRIFTING SNOW OUT WEST. THE SNOW WILL CONTINUE THROUGH THE DAY
MONDAY. LOOKS LIKE WINTER STORM WATCHES WILL BE NEEDED FOR THE
SUNDAY AFTERNOON THROUGH MONDAY AT LEAST AND QUITE POSSIBLY
TUESDAY. WE CAN HANDLE THIS TOMORROW UNLESS THE EVENING CREW FEELS
CONFIDENT ENOUGH TO DO IT THEN. THERE MAY OR MAY NOT BE A LULL ON
MONDAY IN ADVANCE OF THE UPPER LOW ITSELF. EITHER WAY...IT LOOKS
LIKE A LONG DURATION SNOW EVENT THAT BEGINS IN EARNEST SUNDAY
AFTERNOON AND CONTINUES INTO TUESDAY. 12Z GFS IS MUCH WETTER THAN
IT`S PREVIOUS RUN .75 TO 1.5 IN AMOUNTS FAIRLY COMMON IN THE SUN-
MONDAY EVENING TIMEFRAME. EAST OF THE DIVIDE...THE WINDS WILL BE
ON THE INCREASE SUNDAY NIGHT AND MONDAY WITH LEE TROUGHING
DEVELOPING AND INCREASING MID LEVEL FLOW. THE WIND CORRIDOR AND
THE CODY FOOTHILLS WILL SEE QUITE A BIT OF WIND DURING THIS
PERIOD. WILL HAVE TO WATCH THE LOWS SUNDAY NIGHT WITH THOSE AREAS
OF MIXING DOWN WINDS.

MONDAY NIGHT THROUGH FRIDAY

SNOW CONTINUES IN THE WEST...HEAVY AT TIMES...THROUGH TUESDAY BEFORE
THE ACTION SHIFTS EAST OF THE DIVIDE. ARCTIC COLD FRONT IS STILL ON
TRACK TO SAG SWD ON TUESDAY AND ENTRENCH ALL AREAS EAST OF THE
DIVIDE BY AFTERNOON. THE REAL ARCTIC AIR ACTUALLY ARRIVES TUESDAY
NIGHT AND CONTINUES WELL ENTRENCHED THROUGH MIDWEEK. THE 12Z MODEL
RUNS TAKE THE INITIAL UPPER LOW ACROSS MONTANA EARLY IN THE PERIOD
BUT EVEN BEHIND THIS THE ARCTIC HIGH STILL PROVIDES UPSLOPE AND
LIGHT TO MODERATE SNOW EAST OF THE DIVIDE TUESDAY INTO WEDNESDAY. A
HIGH AMPLITUDE RIDGE WILL REMAIN TO OUR WEST THOUGH THROUGH THE
REMAINDER OF THIS PERIOD AND BEYOND WITH SEVERAL SHORTWAVES DROPPING
INTO THE GREAT BASIN KEEPING BITTER COLD AIR OVER THE AREA...ALONG
WITH SOME UPSLOPE AND POSSIBLE LIGHT SNOW OR FLURRIES AT TIMES.
THERE WILL LIKELY BE SOME CLEARING THOUGH BEHIND OUR TUESDAY/
WEDNESDAY SYSTEM TO AID IN A VERY COLD THURSDAY AND PROBABLY FRIDAY
MORNING. CLOUDS AND FLURRIES COULD PROVIDE SOME RELIEF BUT TIMING
THIS IS TOUGH RIGHT NOW. EITHER WAY...DECEMBER WILL START OUT BITTER
COLD WITH PERIODS OF SNOW FOR THE FORESEEABLE FUTURE. H7
TEMPERATURES REMAIN AT OR BELOW -20C ACROSS THE NORTH HALF FROM
WEDNESDAY THROUGH FRIDAY.

&&

.AVIATION.../06Z ISSUANCE/

EAST OF THE CONTINENTAL DIVIDE...
VFR CONDITIONS WILL OCCUR THROUGH 06Z SUNDAY AT THE TERMINAL SITES.
SOME LIGHT SNOW WILL DEVELOP OVER THE HIGHER PEAKS OF THE ABSAROKA
AND WIND RIVER MOUNTAINS AFTER 21Z SATURDAY. THE LIGHT SNOW WILL
INCREASE IN COVERAGE AFTER 03Z SUNDAY WITH MVFR CONDITIONS NEAR THE
MOUNTAINS.

WEST OF THE CONTINENTAL DIVIDE...
VFR CONDITIONS WILL OCCUR THROUGH 06Z SUNDAY AT MOST TERMINAL SITES.
LIGHT SNOW WILL DEVELOP OVER THE MOUNTAINS BY 18Z SATURDAY WITH MVFR
CONDITIONS AT TIMES THROUGH 00Z SUNDAY. AFTER 00Z SUNDAY SNOW WILL
INCREASE OVER THE WESTERN MOUNTAINS WITH MVFR TO IFR CONDITIONS
PREVAILING THROUGH 06Z SUNDAY. AT THE KJAC AIRPORT LIGHT SNOW IS
EXPECTED BY 03Z SUNDAY WITH MVFR CONDITIONS PREVAILING THROUGH 06Z
SUNDAY.

&&

.FIRE WEATHER...

ONE MORE MORNING OF A STRONG SHALLOW TEMPERATURE INVERSION IS
EXPECTED IN THE CENTRAL AND WESTERN BASINS AND VALLEYS TONIGHT AND
SATURDAY MORNING. PERIODS OF LIGHT SNOW WILL DEVELOP LATER TONIGHT
IN THE NORTHWEST MOUNTAINS. LIGHT SNOW SHOWERS CAN BE EXPECTED
SATURDAY IN THE WESTERN MOUNTAINS. BY SUNDAY...HEAVIER ACCUMULATING
SNOW ALONG WITH BLOWING AND DRIFTING SNOW CAN BE EXPECTED IN WESTERN
WYOMING WITH THESE CONDITIONS CONTINUING THROUGH MONDAY NIGHT.
STRONG SOUTHWEST WINDS ARE EXPECTED FROM ROCK SPRINGS TO CASPER AND
ALONG THE EAST SLOPE OF THE CONTINENTAL DIVIDE SUNDAY. AN ARCTIC
COLD FRONT ALONG WITH SNOWFALL WILL SPREAD SOUTHEAST TO AREAS EAST
OF THE DIVIDE MONDAY NIGHT. THE HEAVIEST SNOWFALL WILL OCCUR TUESDAY
NIGHT AND WEDNESDAY EAST OF THE DIVIDE. PERIODS OF LIGHT SNOW WITH
BITTER COLD TEMPERATURES ARE EXPECTED THROUGH THE REST OF NEXT WEEK.

&&

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

&&

$$

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