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000
FXUS65 KRIW 011013
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
313 AM MST SUN DEC 1 2013

.SHORT TERM...SUNDAY THROUGH TUESDAY NIGHT

IN CONTRAST TO MY LAST STRING OF SHIFTS THAT WERE DEAD AS A
DOORNAIL...THIS LOOKS TO BE QUITE AN ACTIVE ONE WITH SNOW...WIND AND
SOME VERY COLD AIR MOVING INTO THE AREA. TO BETTER SUMMARIZE...WE
WILL DIVIDE THE DISCUSSION INTO WEST OF THE DIVIDE AND EAST OF
DIVIDE.

WEST OF THE DIVIDE...THE STORM WILL ARRIVE THERE FIRST. THE FIRST
BATCH OF WARM ADVECTION SNOW MOVED THROUGH THE AREA THIS EVENING
WITH A QUICK INCH OF SNOW IN SOME LOCATIONS. HOWEVER...THE RADAR HAS
REALLY QUIETED DOWN AT THIS POINT WITH THE NEXT BATCH STILL A WAYS
OFF. AS A RESULT...WE HAVE LOWERED POPS AND QPF A BIT THROUGH 11 AM
TODAY. THE NEXT BATCH OF STEADIER AND HEAVIER PRECIPITATION
ASSOCIATED WITH THE NEXT SHORT WAVE AND AIDED BY THE RIGHT REAR QUAD
OF A JET STREAK MOVING BY TO THE NORTH WILL SPREAD SNOW...SOME HEAVY
ACROSS THE WEST. WE WILL HOIST A WINTER STORM WARNING FOR THE AREAS
PREVIOUSLY UNDER A WATCH STARTING AT 11 AM RATHER THAN 5 AM WITH
ONLY LIGHT SNOW EXPECTED BEFORE THAT. THERE COULD BE ANOTHER BRIEF
LULL IN THE SNOW LATER THIS EVENING AND TONIGHT WITH THE BEST
DYNAMICS MOVING OUT BEFORE PICKING UP AGAIN DURING THE DAY ON
MONDAY. WE AGREE WITH THE PREVIOUS SHIFT THAT ANOTHER BURST OF VERY
HEAVY SNOW WILL OCCUR LATER MONDAY AFTERNOON AND MONDAY EVENING WITH
THE ARCTIC FRONT DROPPING SOUTHWARD ACROSS THE AREA AIDED BY A 125
KNOT JET STREAK MOVING INTO THE AREA. THE PREVIOUS DISCUSSION ALSO
MENTIONED THE SNOW MAY TAPER OFF EARLIER AND WE AGREE WITH THAT. THE
STEADY SNOW SHOULD SHUT OFF AFTER THE PASSAGE OF THE ARCTIC FRONT SO
WE WILL END THE WARNING AT 5 AM ON TUESDAY. WE MADE FEW CHANGES PAST
TUESDAY WITH MAINLY LIGHT SNOW SHOWERS CONTINUING THROUGH TUESDAY
NIGHT. TEMPERATURES WILL BE VERY COLD AS WELL WITH FALLING
TEMPERATURES DURING THE DAY A REAL POSSIBILITY WITH THE STRONG COLD
ADVECTION. WITH THIS STORM...SOME FAVORED MOUNTAIN AREAS COULD BE
LOOKING AT 2 TO 3 FEET OF NEW SNOW WITH THIS STORM.

EAST OF THE DIVIDE...A MORE COMPLEX FORECAST ACROSS THIS AREA. TODAY
LOOKS TO BE A DRY DAY WITH THE EXCEPTION OF THE BIGHORN RANGE WHERE
SOME SNOW MAY FALL WITH THE PASSAGE OF THE FIRST SHORTWAVE. WITH THE
PRESSURE GRADIENT TIGHTENING AND 700 MILLIBAR WINDS INCREASING WINDS
WILL INCREASE THROUGH THE DAY ACROSS FAVORED AREAS LIKE THE
SOUTHWESTERN WIND CORRIDOR AS WELL AS DOWNWIND OF THE ABSAROKAS.
THIS INCLUDED EVERYONE`S FAVORITE CROSSROAD...CLARK. THE STRONGEST
WINDS STILL LOOK TO BE LATE TONIGHT AND TOMORROW MORNING FOR AREAS
DOWNWIND OF THE ABSAROKAS...THIS TIME POSSIBLY INCLUDING MORE
POPULATED AREAS LIKE CODY. ACROSS THE WIND CORRIDOR THE THREAT OF
STRONG WINDS WILL CONTINUE THROUGH THE DAY ON MONDAY...INCLUDING
CASPER AS 50 TO 60 KNOT 700 MILLIBAR WINDS MIX TO THE SURFACE. WITH
THE STRONG DOWNSLOPING FLOW...EXPECT A MAINLY DRY AND MILD DAY FOR
MOST AREAS...ESPECIALLY ACROSS THE SOUTHERN TWO THIRDS OF THIS AREA.
SINCE HIGH WINDS WILL HOLD OFF UNTIL TONIGHT...WE WILL CONTINUE THE
HIGH WIND WATCH FOR NOW.

THE MODELS CONTINUE TO BE IN GOOD AGREEMENT THAT THE ARCTIC FRONT
WILL DROP INTO NORTHERN WYOMING TOWARD SUNSET ON MONDAY EVENING
AND THEN PLUNGE SOUTHWARD ACROSS THE STATE ON MONDAY NIGHT. THE
FRONT WILL LIKELY BE ACCOMPANIED BY A HEAVY BURST OF SNOW AS IT
DROPS SOUTHWARD THROUGH THE NIGHT. TUESDAY WILL BE A SLAP IN THE
FACE FOR PEOPLE AS TEMPERATURES WILL BE 20 AND IN SOME CASES 30
DEGREES COLDER THAN THE PREVIOUS AFTERNOON. WITH STRONG COLD
ADVECTION CONTINUING BEHIND THE FRONT...TEMPERATURES WILL FALL
DURING THE DAY. THE SOURCE OF THIS AIR MASS IS FROM SIBERIA WITH
CROSS POLAR FLOW SETTING UP ACROSS THE AREA. AS FOR SNOW...THERE IS
STILL SOME DISAGREEMENT AS TO SPECIFICS. THERE STILL LOOKS TO BE A
BIT OF OVERRUNNING BUT THE MODELS HAVE BACKED OFF ON AMOUNTS A BIT.
FOR NOW WE LOWERED AMOUNTS SLIGHTLY BUT WITH LACK OF CONSISTENCY BIG
CHANGES WERE NOT MADE. MODELS ALSO DIFFER FOR TUESDAY NIGHT WITH THE
GFS AND EUROPEAN SHOWING SOME DECENT SNOW CREEPING BACK INTO MAINLY
SOUTHERN WYOMING WITH THE LEFT FRONT QUAD OF A JET STREAK. THE NAM
KEEPS THIS FEATURE FURTHER SOUTH AND AS A RESULT THINGS MAINLY DRY.
WITH THE UNCERTAINTY...WE LEFT CONTINUITY ALONE. TUESDAY NIGHT LOOKS
TO BE BITTERLY COLD WITH LOWS FALLING BELOW ZERO...IN SOME CASES
WELL BELOW ZERO BY WEDNESDAY MORNING.

.LONG TERM...WEDNESDAY THROUGH SUNDAY

THE FRIGID ARCTIC AIRMASS WILL REMAIN ENTRENCHED ACROSS THE AREA
THROUGH THIS PERIOD.

LONGWAVE TROUGH WILL BE ORIENTED SW-NE ACROSS THE ROCKIES ON
WEDNESDAY WITH EMBEDDED LOWS OVER NORTHERN MONTANA AND THE EASTERN
GREAT BASIN.  H7 LOW NEAR GJT 12Z WEDNESDAY WILL DRIFT EAST ACROSS
COLORADO...A TREND THAT IS FURTHER SOUTH THAN EARLIER MODEL RUNS AND
WILL PLACE HEAVIEST SNOWFALL SOUTH OF WYOMING.  HOWEVER...WIDESPREAD
LIGHT TO MODERATE SNOW IS EXPECTED ACROSS THE SOUTH INTO CENTRAL
WYOMING WEDNESDAY MORNING WITH THE HIGHEST SNOWFALL RATES ALONG AND
SOUTH OF INTERSTATE 80.  SNOW WILL GRADUALLY TAPER OFF WEST TO EAST
WEDNESDAY AFTERNOON AND EVENING.  COLD ARCTIC AIR WILL CONTINUE TO
SURGE SOUTH INTO THE AREA WEDNESDAY AND WEDNESDAY NIGHT WITH MOST
HIGHS ACROSS THE NORTH FROM NEAR ZERO TO 5 ABOVE...WITH SUB-ZERO
READINGS IN THE MOUNTAINS. LOWS WEDNESDAY NIGHT WILL BE MOSTLY
FROM 10 TO 20 BELOW ZERO WITH 20 TO 30 BELOW READINGS ACROSS
YELLOWSTONE NATIONAL PARK.

HIGH AMPLITUDE CROSS-POLAR FLOW WILL RESULT IN NEARLY CONTINUOUS
RIVER OF ARCTIC AIR FLOWING SOUTH INTO THE REGION THROUGH SATURDAY.
THERE WILL BE A FEW EMBEDDED DISTURBANCES THAT WILL BRING SHOTS OF
FLUFF ACROSS THE AREA...MAINLY THE WESTERN MOUNTAINS...FRIDAY AND
SATURDAY.  FORECAST REFLECTS THE SLOWER MORE AMPLIFIED
ECMWF...BRINGING MAIN CLIPPER ACROSS THE AREA FRIDAY NIGHT AND
SATURDAY.  OTHERWISE...IT LOOKS LIKE WE COULD APPROACH RECORD LOWS
AND ESPECIALLY RECORD LOW HIGHS (MOSTLY SET ACROSS MUCH OF THE AREA
DURING AN EXTENDED COLD SNAP IN 1972) DURING THE FIRST WEEK OF
DECEMBER. THOSE RECORD LOW MAXIMUM TEMPERATURES MOSTLY RANGED
FROM ZERO TO 7 BELOW ON DECEMBER 4-5 IN THE CENTRAL BASINS. EXPECT
ONLY A SLIGHT MODIFICATION OF TEMPERATURES WITH AN INCREASE IN
CLOUDS AND SOME LIGHT SNOW FRIDAY AND SATURDAY.

&&

.AVIATION.../12Z ISSUANCE/

EAST OF THE CONTINENTAL DIVIDE...

VFR CONDITIONS WILL OCCUR TODAY AND TONIGHT AT THE TERMINAL SITES.
SNOW WILL OCCUR OVER THE ABSAROKA AND WIND RIVER MOUNTAINS TODAY AND
TONIGHT WITH MVFR TO IFR CONDITIONS. WINDY CONDITIONS AT THE KCPR
TERMINAL SITE DURING MUCH OF THE PERIOD.

WEST OF THE CONTINENTAL DIVIDE...

SNOW WILL OCCUR OVER MOST OF THE WESTERN MOUNTAINS TODAY AND
TONIGHT. MVFR TO IFR CONDITIONS WILL PREVAIL WITH FREQUENT MOUNTAIN
OBSCURATION. THE KJAC TERMINAL SITE WILL BE IMPACTED BY MVFR AND IFR
CONDITIONS AS WELL. AT KRKS TERMINAL SITE WIND WILL BE THE MAIN
IMPACT TODAY AND TONIGHT AS THE WIND SPEEDS WILL BE ON THE INCREASE.
VFR CONDITIONS ARE FORECAST TO PREVAIL AT KRKS TERMINAL SITE.
&&

.FIRE WEATHER...

MILD AND DRY CONDITIONS ARE EXPECTED EAST OF THE DIVIDE THROUGH
MONDAY. VERY STRONG WEST SOUTHWEST WINDS ARE POSSIBLE FROM ROCK
SPRINGS TO CASPER AS WELL AS ALONG THE EAST SLOPE OF THE CONTINENTAL
DIVIDE AND ADJACENT FOOTHILLS MONDAY. SNOWFALL WILL INCREASE IN
THE WESTERN MOUNTAINS TODAY AND CONTINUE THROUGH MONDAY NIGHT WITH
SEVERAL INCHES OF SNOW LIKELY. BITTERLY COLD WEATHER WILL FILTER
INTO THE AREA MONDAY NIGHT THROUGH TUESDAY NIGHT.
&&

.RIW WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WATCH FROM THIS EVENING THROUGH MONDAY AFTERNOON
WYZ019-030.

WINTER STORM WARNING FROM 11 AM THIS MORNING TO 5 AM MST TUESDAY
WYZ001-002-012>014-023>025.

HIGH WIND WATCH FROM THIS EVENING THROUGH MONDAY MORNING WYZ003.

HIGH WIND WATCH FROM LATE TONIGHT THROUGH MONDAY AFTERNOON
WYZ020.

&&

$$

SHORT TERM...HATTINGS
LONG TERM...AEM
AVIATION...AR
FIRE WEATHER...HATTINGS