Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 230338
AFDRIW

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

.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.../00Z ISSUANCE/

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

AREAS OF LLWS WILL CONTINUE OVER THE CENTRAL BASINS AS WEST WINDS
FL070-100 BETWEEN 45-50KTS THROUGH 06Z. THESE STRONGER WINDS WILL
MIX DOWN TO THE SURFACE FROM VCNTY 50NE SM KRKS-KCPR AND FROM
VCNTY KCOD- KDUB WHERE HIGH WIND WARNINGS ARE IN EFFECT. A STRONG
COLD FRONT WILL PUSH ACROSS THE AREA EARLY THIS EVENING. MTNS WILL
BE MOSTLY OBSCURED ALONG THE DIVIDE AHEAD OF THE FRONT WITH SOME
BLOW OVER PCPN IN THE VCNTY OF KLND-KCOD. A BAND OF SNOW WILL
LIKELY ACCOMPANY THE FRONT THIS EVENING ALONG WITH AREAS OF
MVFR/IFR -SN MAINLY VCNTY ALONG AND EAST OF THE BIGHORN RANGE AND
INTERSTATE 25. AREAS OF SFC NW WINDS AT 20-30KTS WITH GUSTS TO
40KTS WILL FOLLOW THE FRONT...DECREASING AFTER 06Z.

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

MVFR/IFR CEILINGS AND VISIBILITIES REDUCED IN SNOW...BLOWING SNOW
AND FOG WILL CONTINUE ACROSS THE WEST THROUGH 18Z SUNDAY.  LLWS
WILL ALSO PERSIST ACROSS THE AREA AS FL070-100 WINDS BTWN
40-50KTS. A STRONG COLD FRONT WILL PUSH ACROSS THE AREA THIS
AFTERNOON AND EVENING WITH AREAS OF WEST SFC WIND 20-30KTS WITH
GUSTS TO 40KTS. MVFR/IFR CEILINGS AND VISIBILITIES WILL DECREASE
ACROSS THE WEST FROM 12Z THROUGH 18Z SUNDAY.

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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