Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 280525
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1125 PM MDT SAT SEP 27 2014

.SHORT TERM...TONIGHT THROUGH SUNDAY

FORECAST ON TRACK WITH LARGE UPPER LEVEL LOW CUTTING OFF OVER
CENTRAL CALIFORNIA AND THE WESTERN GREAT BASIN...SPREADING
SIGNIFICANT SUBTROPICAL MOISTURE NORTH ACROSS UTAH...WESTERN
COLORADO...IDAHO AND SOUTHERN AND WESTERN WYOMING.  THIS AIR MASS
IS UNSTABLE WITH STRONG UPPER LEVEL DIVERGENCE...INCREASING MID
LEVEL DEFORMATION AND FRONTOGENESIS OVER THE AREA. A SURFACE COLD
FRONT HAS MOVED SOUTH TO THE CONTINENTAL DIVIDE AND WILL CONTINUE
TO PUSH THROUGH THE REST OF THE AREA TONIGHT.  CLOUDS AND
PRECIPITATION WILL SPREAD NORTH AND EAST ACROSS THE AREA TONIGHT
AND WILL CONTINUE THROUGH SUNDAY. MUCH OF THE SOUTH AND WEST WILL
EXPERIENCE EMBEDDED THUNDERSTORMS WITH GUSTY WINDS AND SMALL HAIL.
WITH THE CONVECTION BEING SUPPORTED BY THE STRONG UPPER
DIVERGENCE...THE THUNDERSTORMS WILL CONTINUE TO BE A THREAT
THROUGH THE NIGHT.  TEMPERATURES WILL BE GENERALLY COLDER OVER
MUCH OF THE AREA...BUT CLOUD COVER AND PRECIPITATION WILL MODERATE
THE COOLING IN THE WEST. SNOW LEVELS WILL LOWER TO AROUND 9500 FEET
AND REMAIN NEAR THAT LEVEL THROUGH SUNDAY...LOWERING TO 9000 FEET
LATE SUNDAY AFTERNOON. LOCAL HEAVY RAIN IS EXPECTED...ESPECIALLY
IN THE WESTERN AND CENTRAL MOUNTAINS WITH 1 TO 2 INCHES OF RAIN
POSSIBLE THROUGH SUNDAY AFTERNOON.

.LONG TERM...SUNDAY NIGHT THROUGH SATURDAY

THE BEST LIFT AND MOST CONCENTRATED RAIN WITH THE UPPER LEVEL LOW
LIFTING NORTHWARD IS EXPECTED TO LIFT EAST TO NORTHEASTWARD ACROSS
THE AREA ON SUNDAY EVENING. THE MODELS DO HAVE SLIGHT TIMING
DIFFERENCES AND ARA OF HEAVIEST PRECIPITATION. HOWEVER...CONTINUITY
HAD THIS PORTRAYED FAIRLY WELL SO WE MADE FEW CHANGES TO POPS OF
QPF. THE HEAVIEST PRECIPITATION SHOULD SHIFT EAST OF THE AREA LATER
SUNDAY NIGHT WITH LEFTOVER LIGHTER ACTIVITY THROUGH THE OVERNIGHT
HOURS. AS FOR THE CHANCE OF THAT WHITE STUFF STARTING WITH THE
LETTER S...WE AGREE WITH THE PREVIOUS SHIFT THAT THIS IS NOT A
REALLY COLD SYSTEM AND ANY DECENT ACCUMULATIONS WILL BE CONFINED TO
ABOVE PASS LEVELS...AROUND 9500 FEET.

BY MONDAY THE SYSTEM LOOKS MORE LIKE AN OPEN WAVE SITUATION. THE
BEST LIFT AND PRECIPITATION LOOKS TO STAY EAST OF THE AREA.
HOWEVER...THE GFS DOES TRY TO WRAP SOME HEAVIER PRECIPITATION BACK
INTO EASTERN PORTIONS OF THE COUNTY WARNING AREA...MAINLY FROM THE
BIGHORN RANGE AND EASTWARD. THE REST OF THE AREA LOOKS TO HAVE
MAINLY LIGHTER PRECIPITATION. NEVERTHELESS...IT LOOKS LIKE ANOTHER
MAINLY CLOUD AND COOL DAY.

THE MODELS THEN LIFT THE LOW OUT OF THE AREA FOR LATER TUESDAY AND
INTO WEDNESDAY...ALTHOUGH A FEW SHOWERS MAY LINGER IN THE
NORTHEAST. ANOTHER SHORTWAVE LOOKS TO ROTATE INTO THE WEST WITH
ANOTHER CHANCE OF SHOWERS. THIS SYSTEM LOOKS COLDER AND COULD LOWER
SNOW LEVELS DOWN TO AROUND 7500 FEET HOWEVER. THERE IS MUCH LESS
MOISTURE TO WORK WITH HOWEVER SO NO HIGHLIGHTS ARE ANTICIPATED AT
THIS TIME. CONTINUITY LOOKED REASONABLE SO WE MADE FEW CHANGES.

YET ANOTHER FAST MOVING CLIPPER WILL MOVE SOUTHEASTWARD TOWARD THE
AREA FOR THURSDAY. THE MODELS CONTINUE TO HAVE DIFFERENCES AS
EXPECTED WITH THE EUROPEAN FURTHER SOUTH WITH THE GFS KEEPING THINGS
FURTHER NORTH. WITH THE UNCERTAINTY...WE CONFINED POPS MAINLY TO THE
NORTHERN HALF OF THE COUNTY WARNING AREA. AGAIN...THIS SYSTEM DOES
NOT HAVE MUCH MOISTURE SO ANY PRECIPITATION IS EXPECTED TO BE
LIGHT.  QUIETER WEATHER SHOULD FINALLY THEN MOVE IN FOR FRIDAY AND
NEXT WEEKEND AS RIDGING REBUILDS ACROSS THE WEST AND BRINGS DRY
CONDITIONS WITH WARMER TEMPERATURE.

&&

.AVIATION.../06Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

WIDESPREAD MVFR/SOME IFR CEILINGS WILL DEVELOP BY 10Z ACROSS MUCH OF
THE AREA AND LAST THROUGH AT LEAST 18Z...WITH WIDELY SCATTERED
SHOWERS. THE MAIN EXCEPTION WILL BE ACROSS THE WIND RIVER BASIN
WHERE MORE WIDESPREAD -SHRA SHOULD OCCUR. DURING SUNDAY
AFTERNOON...CEILINGS WILL TRY TO LIFT TO LOW VFR...BUT A LARGE AREA
OF CONVECTION ACROSS SOUTHWEST WYOMING IN THE MORNING WILL BEGIN TO
OVERSPREAD AREAS EAST OF THE DIVIDE IN THE AFTERNOON. THIS LARGE
AREA OF CONVECTION SHOULD GENERALLY IMPACT CENTRAL WYOMING IN THE
MID AFTERNOON AND SPREAD INTO THE NORTHEAST/NORTH WYOMING IN THE
EARLY TO MID EVENING. AREAS TO THE NORTH AND EAST OF THIS CONVECTION
IN THE AFTERNOON COULD SEE SOME LOW VFR CEILINGS DEVELOP...BEFORE
RETURNING TO MVFR/IFR CONDITIONS WITH THE SHRA/VCTS. THIS ACTIVITY
SHOULD LAST BETWEEN 2 AND 4 HOURS...BEFORE LIFTING AWAY. EVEN AFTER
THIS ACTIVITY DEPARTS...BOUNDARY LAYER MOISTURE WILL REMAIN
HIGH...KEEPING GOOD CHANCES OF LOW CEILINGS AND POSSIBLY SOME FOG IN
THE MIX THROUGH 12Z MONDAY. MOUNTAINS WILL BE OBSCURED THROUGH THE
PERIOD...AND ICING WILL BE A MAJOR CONCERN OVER HIGH MOUNTAIN
PASSES.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

NUMEROUS SHRA AND POSSIBLY ISOLATED TSRA WILL CONTINUE OVERNIGHT
THROUGH SUNDAY MORNING. THE MOST ACTIVE AREA WILL BE SOUTH OF A
KJAC-KPNA-30NE KRKS WHERE PERIODS OF MVFR/IFR CONDITIONS WILL OCCUR.
NOT MUCH CHANGE THROUGH THE DAY SUNDAY UNTIL AFTER 21Z WHEN THE
LARGE AREA OF CONVECTION BEGINS TO LIFT NORTH AND NORTHEAST AWAY
FROM THE AREA. ALTHOUGH THE PERSISTENT SHRA SHOULD GRADUALLY COME TO
AN END LATE IN THE AFTERNOON/EARLY EVENING...ISOLATED TO SCATTERED
CONVECTION WITH THE UPPER LOW SHOULD PERSIST FOR MUCH OF TONIGHT.
MOUNTAINS WILL BE OBSCURED THROUGH THE PERIOD...AND ICING WILL BE A
MAJOR CONCERN GOING OVER HIGH MOUNTAIN PASSES.

&&

.FIRE WEATHER...

COLDER AND WETTER WEATHER WILL SPREAD OVER THE AREA TONIGHT AND WILL
THEN CONTINUE INTO TUESDAY...WITH SNOW LEVELS LOWERING EACH NIGHT IN
THE MOUNTAINS FROM AROUND 9500 FEET TONIGHT...TO 8500 FEET MONDAY
NIGHT.

&&

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

&&

$$

SHORT TERM...C.BAKER
LONG TERM...HATTINGS
AVIATION...WM
FIRE WEATHER...C.BAKER










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