Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 230636
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1134 PM MST SAT NOV 22 2014

.UPDATE...UPDATED TO ADD 06Z AVIATION DISCUSSION.

.UPDATE...SNOW HAS TAPERED OFF OR ENDED BEHIND A COLD FRONT ACROSS
MOST OF WESTERN WYOMING. ANOTHER SHORTWAVE MOVING EAST ACROSS
IDAHO WILL BRING ANOTHER SHOT OF LIGHT TO MODERATE SNOW INTO FAR
WEST WYOMING AFTER MIDNIGHT. CANCELLED WINTER HIGHLIGHTS FOR ALL
AREAS BUT JACKSON HOLE VALLEY...STAR VALLEY AND SURROUNDING
MOUNTAINS WHERE WINTER STORM WARNINGS REMAIN IN EFFECT UNTIL 6 AM
SUNDAY. COLD FRONT HAS ALSO ENDED THE HIGH WIND THREAT ACROSS
CENTRAL WYOMING...SO HIGH WIND WARNINGS WERE CANCELLED. UPGRADED
HIGH WIND WATCH TO A WARNING FOR ONLY NORTHEAST JOHNSON COUNTY ON
SUNDAY. LATEST MODEL RUNS NOT AS BULLISH WITH STRONG WINDS FURTHER
WEST ACROSS THE WIND RIVER BASIN.

&&

.PREV DISCUSSION... /ISSUED 210 PM MST SAT NOV 22 2014/

SHORT TERM...TONIGHT THROUGH SUNDAY

A PACIFIC COLD FRONT APPROACHING WESTERN WYOMING WILL MOVE THROUGH
WESTERN AND CENTRAL WYOMING THROUGH THE NIGHT.  THE SNOW INTENSITIES
WILL DECREASE WITH THE PASSING OF THE COLD FRONT IN THE WESTERN
M0MOUNTAINS.  MOST AREAS EXPERIENCING HIGH WINDS TODAY WILL SEE
WINDS DECREASE AS THEY SHIFT TO THE NORTHWEST. HIGH WIND WATCHES
REMAIN FOR NORTHERN JOHNSON AND THE WIND RIVER BASIN WITH THE
NORTHWEST WINDS AS THESE AREAS FAVOR HIGH WINDS WITH NORTHWEST
WINDS AND COLD AIR ADVECTION. AREAS EAST OF THE CONTINENTAL DIVIDE
CAN EXPECT A QUICK BURST OF SNOWFALL BEHIND THE COLD FRONT WITH
LIGHT ACCUMULATIONS. OVERALL SNOWFALL WILL BE TAPERING OFF
THROUGH THE MORNING WITH SOME LINGERING MOUNTAIN SNOW SHOWERS ON
SUNDAY. TEMPERATURES WILL COOL ABOUT TEN DEGREES FROM TODAY.

LONG TERM...SUNDAY NIGHT THROUGH SATURDAY

BEHIND THE MAIN SHORTWAVE THAT WILL BE SWINGING THROUGH THIS
WEEKEND...A SECONDARY PIECE OF ENERGY WILL BE SLIDING DOWN THE BACK
SIDE OF THE MAIN TROUGH AXIS ACROSS THE CWA FAIRLY QUICKLY AROUND
12Z MONDAY. WITH WEAK ISENTROPIC LIFT IN THE WEST AHEAD OF THIS
SYSTEM AS WELL AS SOME WEAK QG FORCING IN THE SOUTHWEST...KEPT IDEA
OF ANOTHER 3 TO 6 INCHES OF SNOWFALL IN THE WESTERN MTNS SUNDAY INTO
MONDAY ALONG WITH ANOTHER 2 TO 3 INCHES IN THE WESTERN VALLEYS. THE
SNOW INTENSITY WILL BEGIN TO DECREASE MONDAY AFTERNOON. DURING THE
TROUGH PASSAGE...AROUND 12Z MONDAY...THERE WILL BE A BRIEF PERIOD WHEN THE
SNOWFALL SPILLS OVER TO AREAS EAST OF THE DIVIDE WITH THE MOST
SIGNIFICANT SNOWFALL OCCURRING IN THE BIG HORN MTNS WHERE 3 TO 5
INCHES ARE EXPECTED. THE SNOWFALL WILL DECREASE EAST OF THE DIVIDE
IN THE AFTERNOON AS WELL.

THE NEXT ANTICIPATED SNOW EVENT WILL OCCUR WHEN THE JET STREAM
SHIFTS NORTHEAST PLACING THE FASTER NORTHWEST FLOW ALOFT OVER
WYOMING BY 12Z TUESDAY. THIS WILL DRAW IN ADDITIONAL PACIFIC
MOISTURE FROM THE NORTHWEST ALONG WITH ISENTROPIC LIFT OVER WESTERN
WY TUESDAY WITH AN EXTENSIVE AREA OF ISENTROPIC LIFT SHIFTING TO OUR
NORTH OVER MONTANA BY TUESDAY NIGHT. THIS WILL JUSTIFY LIKELY POPS
IN THE WESTERN/BIG HORN MTNS AS WELL AS CHC POPS OVER THE NORTH HALF
OF THE LOWER ELEVATIONS OF THE CWA TUE/TUE NIGHT. THE JET STREAM
WILL THEN SHIFT NORTHEAST OF THE CWA BY WEDNESDAY.

AFTER THIS TIME FRAME...THE MODELS DIVERGE ONCE AGAIN WITH THE EURO
NOW THE MORE OPTIMISTIC MODEL PLACING A RIDGE OVER WY BY THURSDAY
AND THE GFS KEEPING THE DIRTY NORTHWEST FLOW OVER US THROUGH FRIDAY
WHICH IS IRONIC BECAUSE A COUPLE OF DAYS AGO BOTH THESE MODELS
PORTRAYED OPPOSITE SOLNS WITH THE GFS ADVERTISING A BUILDING RIDGE
AND THE EURO A POTENTIAL SNOW EVENT FOR THANKSGIVING. WITH THE
MODELS FLIP FLOPPING AND NO RUN TO RUN CONSISTENCY...ALL WE ARE
GOING TO DO IS INCREASE THE POPS A TAD OVER MAINLY NW WY FOR THE
SECOND HALF OF NEXT WEEK JUST IN CASE A SNOW EVENT DOES TAKE PLACE
DURING THIS TIME FRAME. MORE SPECIFICALLY...THE GFS PULLS IN COLDER
AIR FROM THE NORTHEAST OVER WY WITH MOST OF THE ASCT ISENTROPIC LIFT
FROM THIS ASCT WEATHER DISTURBANCE REMAINING TO OUR NORTH UP IN MT.

BY FRIDAY NIGHT...THE NW FLOW WILL BACK TO THE WEST AS THE RIDGE
FLATTENS. A MINOR DISTURBANCE MOVING THROUGH THE FLATTENING RIDGE
WITH ITS SHARE OF ISENTROPIC LIFT COULD BRING SOME LIGHT SNOW TO THE
FAR WEST SATURDAY.

TEMPERATURES NEXT WEEK WILL DEPEND LARGELY UPON WHETHER THE GFS OR
THE EURO PANS OUT SO KIND OF WENT WITH A BLEND. IN ANY EVENT...TEMPS
WILL BE MUCH MILDER THAN THEY HAVE BEEN DURING THE LAST COUPLE OF
WEEKS GIVEN THE LACK OF ANY ARCTIC INTRUSIONS NEXT WEEK.

AVIATION.../06Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES
VFR CONDITIONS WILL PREVAIL THROUGH MID-MORNING SUNDAY BEHIND A COLD
FRONT THAT MOVED THROUGH THE AREA SATURDAY EVENING.  AN UPPER LEVEL
DISTURBANCE WILL SPREAD SHSN INTO THE BIGHORN RANGE...FRQT MTN
OBSCURATIONS BY 18Z SUNDAY WITH ISOLD TO WIDELY SCT MVFR -SHSN
MAINLY VCNTY AND EAST OF A KCOD-KWRL-KCPR LINE.  NW SFC WINDS WILL
INCREASE WITH THIS SYSTEM MID TO LATE SUNDAY MORNING WITH WIND GUSTS
OVER 50KTS EXPECTED ALONG AND NORTH OF THE I90 CORRIDOR.  FURTHER
WEST...SFC NW WINDS AT 20-30KTS WITH GUSTS TO 40KTS WILL OCCUR
ACROSS THE WIND RIVER BASIN...VCNTY KRIW.  WINDS WILL DECREASE BUT
REMAIN GUSTY IN THESE AREAS SUNDAY NIGHT.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES
A WEAK UPPER LEVEL DISTURBANCE WILL SLIDE ACROSS W-SW WYOMING EARLY
THIS MORNING SPREADING AREAS OF MVFR/IFR -SN AND MTN OBSCURATIONS
INTO VCNTY KJAC-KAFO THROUGH AROUND 13Z.  A BAND OF MVFR/IFR SNOW IS
ALSO LIKELY TO MOVE EAST ALONG THE INTERSTATE 80 CORRIDOR...VCNTY
KRKS 10Z-15Z.  A DRIER AIRMASS WILL FOLLOW LATE SUNDAY MORNING AND
SUNDAY AFTERNOON WITH SOME LINGERING SNOW SHOWERS OBSCURING MTNS.
GUSTY NW SFC WINDS AT 20-30KTS WILL ALSO DEVELOP BEHIND THIS SYSTEM
DURING THE DAY SUNDAY ACROSS THE UPPER GREEN RIVER BASIN AND ALONG
THE INTERSTATE 80 CORRIDOR.  A MOIST WESTERLY FLOW WILL SPREAD AREAS
OF MVFR/IFR -SN BACK INTO THE WEST...MAINLY VCNTY AND NORTH OF A
KEMM-KPNA LINE SUNDAY NIGHT.

FIRE WEATHER...

SNOWFALL WILL CONTINUE MOST MOUNTAIN AREAS TONIGHT AND THEN
DECREASE THROUGH SUNDAY AS A COLD FRONT PASSES THROUGH.  STRONG WINDS
WILL CONTINUE EARLY THIS EVENING AND THEN DIMINISH. BEHIND THE
COLD FRONT EARLY SUNDAY...HIGH WINDS MAY DEVELOP IN THE WIND
RIVER BASIN AND NORTHERN JOHNSON COUNTIES AS THESE AREAS FAVOR
STRONGER WINDS IN NORTHWEST FLOW. TEMPERATURES WILL BE COLDER WITH
HIGHER HUMIDITY AND LOW MIXING HEIGHTS WITH POOR SMOKE DISPERSAL.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WARNING UNTIL 6 AM MST SUNDAY WYZ012-013-023-024.

HIGH WIND WARNING FROM 5 AM TO 5 PM MST SUNDAY WYZ010.

&&

$$

UPDATE...AEM
SHORT TERM...C.BAKER
LONG TERM...LIPSON
AVIATION...C.BAKER
FIRE WEATHER...C.BAKER








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