Area Forecast Discussion
Issued by NWS Riverton, WY

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905
FXUS65 KRIW 081700
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1000 AM MST MON FEB 8 2016

.SHORT TERM...TODAY THROUGH WEDNESDAY NIGHT

NW WINDS HAVE BEEN BLOWING FAIRLY STEADILY ACROSS THE UPPER
WIND RIVER BASIN FROM CROWHEART TO DUBOIS AS WELL AS IN THE VCNTY
OF PINEDALE IN RESPONSE TO THE RELATIVELY TIGHT SFC PRESSURE
GRADIENT PRODUCED BY THE SFC HIGH CONTINUING TO BUILD IN FROM THE
WEST. THE HEART OF THE WIND RIVER AND UPPER GREEN RIVER BASINS
ARE NO LONGER MIXED WITH LIGHT OR CALM WINDS. CURRENTLY IT IS 10
DEGREES 2 MILES SOUTH OF RIVERTON AND 37 IN CROWHEART AS
INVERSIONS REESTABLISH THEMSELVES AMONGST SNOW COVER. SOUTHWEST
WINDS WILL RETURN FROM RKS TO CPR TODAY AS A SFC LEE SIDE TROUGH
BEGINS TO DEVELOP. WITH TEMPERATURE INVERSIONS STRENGTHENING BY
12Z TUESDAY AND DRY AIR JUST ABOVE THE SURFACE...BASINS AND
VALLEYS THAT STILL MAINTAIN SNOWCOVER WILL LIKELY SEE PATCHY FOG
LATE TONIGHT AND TUESDAY MORNING AS WELL AS LATE TUE NT AND WED
MORNING. TEMPS WILL WARM THROUGH THE MIDDLE OF THE WORK WEEK WITH
BASINS AND VALLEYS LAGGING A DAY OR SO BEHIND AS HIGH PRESSURE
CONTINUES TO BUILD IN FROM THE WEST. NEAR RECORD HIGHS IN THE 50S
AND 60S ARE NOT OUT OF THE REALM OF POSSIBILITIES FOR MIXED AREAS
LIKE CPR AND BYG RESPECTIVELY EAST OF THE DIVIDE BY WED AFTERNOON.
WINDY CONDITIONS WILL LIKELY RETURN FROM THE RED DESERT TO CPR
WEDNESDAY AS THE RIDGE FLATTENS.

.LONG TERM...THURSDAY THROUGH MONDAY

SYNOPSIS...UPPER RIDGE WILL CONTINUE TO PREVAIL OVER THE AREA
THROUGH FRIDAY WITH DRY WEATHER AND UNSEASONABLY WARM TEMPERATURES
OVER MOST OF THE AREA. INVERSIONS WILL LIKELY HOLD BUT WEAKEN OVER
COLDER FAR WEST VALLEYS. A PACIFIC COLD FRONT WILL MOVE ACROSS THE
AREA SATURDAY NIGHT BRINGING CHANCES OF SNOW SHOWERS TO THE WEST
AND NORTHERN MOUNTAINS. A RIDGE OF HIGH PRESSURE WILL REBUILD OVER
THE AREA EARLY NEXT WEEK.

DISCUSSION...ECMWF AND GFS IN GOOD OVERALL AGREEMENT THROUGH FRIDAY
WITH UPPER RIDGE OVER THE AREA.  DIFFERENCES ARISE WITH THE NEXT
PACIFIC TROUGH SPLITTING ALONG THE WEST COAST ON SATURDAY AND
SUNDAY.

SHORTWAVE TOPPING THE RIDGE AND DIVING INTO THE NORTHERN PLAINS ON
THURSDAY WILL PROVIDE BETTER MIXING ACROSS THE LOWER CENTRAL BASINS
WITH INCREASING NW WINDS AND COLD ADVECTION IN THE MID-LEVELS.  ONLY
THE NORTHERN BIGHORN RANGE MAY RECEIVE SOME LIGHT SNOW SHOWERS
WITH THIS CLIPPER. TEMPERATURES IN THE FAR WEST VALLEYS THAT MAY
BE TRAPPED UNDER STEEP INVERSIONS IN THE SHORT-TERM COULD MODERATE
AS WELL THURSDAY AND FRIDAY WITH WARM ADVECTION LIKELY BRINGING
SOME BKN-OVC STRATUS DECKS INTO THE AREA.

BOTH GFS AND ECMWF SHOW A GREATER DEGREE OF SPLITTING WITH NEXT
PACIFIC SHORTWAVE MOVING ACROSS THE EASTERN PACIFIC FRIDAY.  ECMWF
CONTINUES TO SHOW STRONGER NORTHERN STREAM SHORTWAVE DIVING ACROSS
THE AREA SATURDAY NIGHT WHILE GFS DAMPENS OUT THE NORTHERN STREAM TO
A MUCH GREATER DEGREE.  GFS SOLUTION KEEP WYOMING DRY WITH A MUCH
WEAKER FRONTAL PASSAGE.  ECMWF HAS SHOWN BETTER RUN-TO-RUN
CONSISTENCY WITH ITS STRONG FRONTAL PASSAGE.  NO MAJOR CHANGES TO
GOING FORECAST THAT IS MORE IN LINE WITH THE ECMWF WITH INCREASING
CHANCES OF SNOW SHOWERS ACROSS THE WEST AND FAR NORTH WITH THE
FRONTAL PASSAGE. ONLY SLIGHT COOLING BEHIND THE FRONT ON SUNDAY WITH
BREEZY TO WINDY AREAS.

&&

.AVIATION.../18Z ISSUANCE/

VFR CONDITIONS TO PREVAIL THROUGH THE FORECAST PERIOD. THE MAIN
CONCERN TODAY WILL BE MARGINAL LOW LEVEL WIND SHEAR NEAR MOUNTAINS
AND MOUNTAIN TURBULENCE DUE TO THE STRONG NORTHWEST TO NORTH FLOW
ALOFT. SOME PATCHY FOG/LOW CLOUD DEVELOPMENT REMAINS A POSSIBILITY
OVER THE FAR WESTERN VALLEYS...AND PERHAPS OVER THE CENTRAL/NORTHERN
WIND RIVER VALLEY TONIGHT. WILL INSERT VCFG INTO THE KJAC AND KRIW
TERMINAL SITES FOR LATE TONIGHT...BUT KEEP IT OUT OF THE UPPER GREEN
RIVER BASIN DUE TO THE EXPECTED CONTINUATION OF BREEZY NORTHERLY
WINDS IN THAT AREA.

&&

.FIRE WEATHER...

HIGH PRESSURE WILL REMAIN THE WEATHER STORY FOR THE NEXT FEW
DAYS. SOME GUSTY WIND WILL BE POSSIBLE DURING THE AFTERNOONS...WITH
OTHERWISE QUIET CONDITIONS. MIXING HEIGHTS WILL REMAIN LOW THROUGH
THIS TIME RESULTING IN MORE WIDESPREAD POOR SMOKE DISPERSION. THE
MAIN EXCEPTIONS WILL BE AT SOME FAVORED FOOTHILL LOCATIONS AS WELL
AS FROM ROCK SPRINGS TO CASPER WHICH MAY SEE PERIODS OF FAIR
SMOKE DISPERSAL WITH THE PRESENCE OF GUSTY WIND.

&&

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

$$

SHORT TERM...LIPSON
LONG TERM...AEM
AVIATION...JB
FIRE WEATHER...LIPSON



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