Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 200553
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1051 PM MST WED NOV 19 2014

UPDATE...UPDATED TO ADD 06Z AVIATION DISCUSSION

.SHORT TERM...TONIGHT THROUGH THURSDAY (ISSUED AT 158 PM MST)

DRY NORTHWEST FLOW ALOFT WILL CONTINUE TO BRING AREAS OF MID AND
UPPER LEVEL CLOUD COVER TO WESTERN AND CENTRAL WYOMING.  AREAS IMPACTED
BY STRONG INVERSIONS ARE GRADUALLY DECREASING WITH STRONG TEMPERATURE
AND WIND GRADIENTS EXISTING BOTH HORIZONTALLY AND VERTICALLY. THE COLDER
TRAPPED AREAS WILL CONTINUE TO SEE LOCAL LOW STRATUS CLOUDS AND
FOG AT NIGHT AND IN THE MORNING WITH GENERALLY LIGHT WINDS.  THE
MIXED AREAS WILL BE 15 TO 20 DEGREES WARMER THAN THE TRAPPED
VALLEYS AND BASINS AT TIMES. DRY CONDITIONS WILL PREVAIL EXCEPT
FOR SOME LIGHT SNOW SHOWERS MOVING INTO THE FAR WEST MOUNTAINS
THURSDAY AFTERNOON. THE MAIN COLD POOLS ARE IN THE FAR NORTH WIND RIVER
BASIN AND THE EASTERN BIGHORN BASIN.

.LONG TERM...THURSDAY NIGHT THROUGH WEDNESDAY

A FAIRLY QUIET BEGINNING TO THE PERIOD. A WEAK DISTURBANCE WILL MOVE
INTO THE WESTERN HALF OF THE STATE THURSDAY EVENING...BUT IS
EXPECTED TO BRING LIMITED PRECIPITATION. SHOWERS SHOULD MAINLY
IMPACT THE WESTERN MOUNTAINS. THE PASSAGE OF THE SYSTEM WILL PERMIT
SOME COOLING TEMPERATURES TO BE FOUND ACROSS THE AREA
FRIDAY...THOUGH CENTRAL BASINS MAY SEE A BIT OF WARMING THANKS TO
BREAK THEIR INVERSION.

THE BIGGER STORY REMAINS SATURDAY AND SUNDAY AS A STRONGER SYSTEM
MOVES INTO THE STATE. MOISTURE FROM A NEARBY WAVE OF LOW PRESSURE
WILL IMPACT THE WESTERN MOUNTAINS SATURDAY MORNING AND
AFTERNOON...WITH SHOWER COVERAGE INCREASING THROUGH THE DAY AND
EVENING. SHOWERS WILL MOVE EAST OF THE DIVIDE BY SATURDAY
EVENING...WITH COOLER TEMPERATURES EXPECTED.

SATURDAY NIGHT THROUGH WEDNESDAY EVENING...LINGERING SNOW SHOWERS
WILL CONTINUE ACROSS WESTERN...SOUTHERN...AND A FEW NORTHERN PORTIONS
BEHIND THE PASSAGE OF SATURDAYS COLD FRONT. SNOW WILL DIMINISH EAST
OF THE DIVIDE THROUGH THE DAY SUNDAY...HOWEVER...MOIST NORTHWESTERLY
FLOW CLOUD LINGER SNOW SHOWERS ACROSS THE WESTERN MOUNTAINS. A FEW
EMBEDDED DISTURBANCES IN THIS FLOW COULD ALSO LINGER SOME LIGHT SNOW
ACROSS THE WESTERN VAL LIES THROUGH THE DAY. THE STRONG JET...THEN
SHIFTS SLIGHTLY NORTHWARD FOR MONDAY...AS THE CUTOFF LOW ACROSS THE
NORTHERN PLAINS PROGRESSES SLIGHTLY EASTWARD. WEAK DISTURBANCES
CAUGHT UP IN THE RESULTANT NORTHWEST FLOW...COMBINED WITH A WEAK
FRONTAL BOUNDARY...WILL BRING AN INCREASED CHANCE FOR SNOW ACROSS
THE WEST...AND INTO PORTIONS OF NORTHERN WYOMING...WITH PERHAPS ONLY
BRIEF LIGHT SNOW ELSEWHERE. BY TUESDAY THE STRONG JET IS THEN PRETTY
MUCH OVERHEAD. A SHIFT TO MORE WESTERLY FLOW COULD BRING BREEZY
CONDITIONS ACROSS THE USUAL WIND CORRIDORS. MOIST WESTERLY FLOW
COULD ALSO CONTINUE SNOW ACROSS THE WESTERN MOUNTAINS. THE POSITIVE
ABOUT SATURDAYS DISTURBANCE IS IT WILL BRING A SLIGHTLY WARMER AIR
MASS INTO THE REGION...COMPARED TO LAST WEEKS ARCTIC AIR THAT
LINGERED. EXPECT TEMPERATURES TO BE SEASONAL TO SLIGHTLY BELOW
NORMAL INTO NEXT WEEK.

MODELS CONTINUE TO DIVERGE WEDNESDAY INTO THANKSGIVING. BOTH ARE NOW
INDICATING AT LEAST A CHANCE FOR SNOW WEDNESDAY AND THANKSGIVING BUT
FOR DIFFERING REASONS. GFS SOLUTION NOW SWINGS A COLD FRONT DOWN
FROM CANADA WEDNESDAY THROUGH THURSDAY MORNING...THAT COULD BRING
A MORE BRIEF SHOT OF SNOW AND COLD. ECMWF IS STILL SHOWING A
STRONG 700 MB LOW IMPACTING THE AREA...WHICH WOULD BRING MORE OF A
WIDESPREAD SNOW IMPACT THAN THE GFS SOLUTION. COMPROMISED ON POPS
FOR NOW...BUT BOTH OF THESE SOLUTIONS WILL CONTINUED TO BE
MONITORED.

&&

.AVIATION.../06Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES
PATCHY IFR/LIFR FOG WILL PARTIALLY OBSCURE LOWER RIVER VALLEYS
MAINLY VCNTY AND NORTH OF KRIW-VCNTY KWRL/KGEY THROUGH 16Z.
OTHERWISE EXPECT VFR CONDITIONS WITH INCREASING MID CLOUDS...AREAS
CIGS AT FL110-140...FROM AROUND 18Z THUR-06Z FRI WITH
CLEARING...PATCHY FOG REDEVELOPING IN THE SAME AREAS EARLY FRIDAY
MORNING.


WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES
PATCHY IFR/LIFR FOG MAY PARTIALLY OBSCURE TERRAIN VCNTY KJAC THROUGH
16Z. A WEAK UPPER LEVEL DISTURBANCE WILL BRING INCREASING MID-LEVEL
CLOUDS...CIGS PRIMARILY FL110-130...ACROSS THE AREA 14Z THURSDAY
-03Z FRIDAY ALONG WITH PARTIAL MTN OBSCURATIONS IN -SN AND LCL MVFR
CONDITIONS.  A WESTERLY FLOW WILL FOLLOW 03Z-12Z FRIDAY WITH DRYING
IN THE MID-LEVELS.  HOWEVER THE BOUNDARY LAYER WILL REMAIN NEARLY
SATURATED IN UPSLOPE FLOW...SO AREAS OF MVFR/IFR CONDITIONS IN -SN
OR FLURRIES WILL LINGER INTO FRIDAY MORNING...ESPECIALLY VCNTY KJAC
NORTH ACROSS YELLOWSTONE NATIONAL PARK.


&&

.FIRE WEATHER...

NORTH NORTHWEST FLOW ALOFT WILL CONTINUE TO BRING AREAS OF MID AND
UPPER LEVEL CLOUD COVER TO WESTERN AND CENTRAL WYOMING.  AREAS IMPACTED
BY STRONG INVERSIONS ARE GRADUALLY DECREASING WITH STRONG TEMPERATURE
AND WIND GRADIENTS EXISTING BOTH HORIZONTALLY AND VERTICALLY. THE COLDER
TRAPPED AREAS WILL CONTINUE TO SEE LOCAL LOW STRATUS CLOUDS AND
FOG WITH GENERALLY LIGHT WINDS AND VERY LOW MIXING HEIGHTS AND
POOR SMOKE DISPERSAL. THE MIXED AREAS WILL BE 20 TO 30 DEGREES
WARMER THAN THE TRAPPED VALLEYS AND BASINS AT TIMES WITH SIGNIFICANTLY
LOWER RELATIVE HUMIDITY AND STRONG GUSTY WINDS. DRY CONDITIONS
WILL PREVAIL. THE MAIN COLD POOLS ARE IN THE FAR NORTH WIND RIVER
BASIN AND THE EASTERN BIGHORN BASIN.

&&

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

$$

SHORT TERM...C.BAKER
LONG TERM...BRANHAM/ANGLIN
AVIATION...AEM
FIRE WEATHER...C.BAKER

















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