Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 220500
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1100 PM MDT TUE OCT 21 2014

.SHORT TERM...TONIGHT THROUGH WEDNESDAY

A COUPLE OF CONVECTIVE BANDS ASCT WITH A PACIFIC COLD
FRONT/VIGOROUS UPPER LEVEL SHORTWAVE PLOWED EAST ACROSS WESTERN WY
THIS MORNING EACH WITH ISOLD LTG STRIKES AND SOME BRIEF HEAVY
RAINFALL IN SOME AREAS. A SKIFF OF SNOW ON THE GROUND WAS NOTED AT
WIND RIVER LAKE. THE SHOWERS WERE DRYING OUT AS THEY CROSS THE
DIVIDE. HOWEVER...THUNDERSTORMS WITH 50 MPH WINDS HAVE DEVELOPED
ACROSS THE WIND RIVER BASIN AND EXTEND DOWN INTO SWEETWATER COUNTY
AS INSTABILITY HAS TRUMPED THE DOWNSLOPE DRYING EFFECT. A WELL
DEVELOPED CIRCULATION IS SEEN OVER CENTRAL IDAHO. LONG AFTER THE
DRY SLOT BEHIND THE AFOREMENTIONED CONVECTION PUNCHES INTO WEST
CENTRAL AND SOUTHWEST WY...WRAP AROUND FROM THE CIRCULATION NOW IN
IDAHO WILL CONTINUE THE THREAT OF MAINLY SNOW SHOWERS IN NW WY AS
THE SNOW LEVEL DROPS TO 6500 FEET THIS EVENING WITH THESE SHOWERS
DIMINISHING AFTER MIDNIGHT TONIGHT. MOST OF THE QG FORCING WITH
THIS WX SYSTEM WILL REMAIN UP IN MONTANA SO EXPECTING MAINLY LIGHT
PRECIP AMOUNTS TONIGHT IN NW WY. HIGH TEMPERATURES WEDNESDAY
BEHIND TODAYS COLD FRONT WILL BE ABOUT THE SAME OUT WEST WHERE
CLOUDS AND SHOWERS HAVE KEPT THOSE AREAS ON THE COOL SIDE
TODAY...BUT WILL AVERAGE ABOUT 10 DEGREES COOLER EAST OF THE
DIVIDE. EXPECT SOME WESTERLY BREEZES FROM KRKS TO KCPR AND AT THE
HIGHER ELEVATIONS EXPECTED WEDNESDAY.

.LONG TERM...WEDNESDAY NIGHT THROUGH TUESDAY

BRIEF RIDGING OVER THE AREA WEDNESDAY NIGHT BEFORE INCREASING SW
FLOW ALOFT DEVELOPS. LEE TROUGHING DEVELOPS AS SEVERAL RIPPLES IN
THE FLOW MOVE TO OUR WEST AND NORTH. A STRONG UPPER JET THEN PUSHES
JUST TO THE NORTH LEAVING OUR NRN ZONES IN THE RIGHT EXIT REGION.
CROSS SECTIONS SHOW SOME DECENT 30-40KT MTN TOP FLOW ALONG THE
ABSAROKAS WITH SOME POTENTIAL FOR A WAVE INDUCED CRITICAL LAYER. NOT
SEEING ANY SUSTAINED MOUNTAIN TOP INVERSION BUT AT LEAST SOME
POTENTIAL FOR A DOWNSLOPE WIND EVENT BASED ON THE SOUNDINGS AND
CROSS SECTIONS. RIGHT NOW...JUST LEANING TOWARDS INCREASED WINDS IN
THE FORECAST THURSDAY INTO THURSDAY NIGHT ALONG WITH SPECIFIC
WORDING IN THE HWO FOR WIND GUSTS TO 50 MPH OR MORE ALONG THE CODY
FOOTHILLS MAINLY LATE THURSDAY OR THURSDAY NIGHT. ANOTHER WEAK
RIPPLE MAY ACTUALLY PUSH A WEAK FRONTAL BOUNDARY INTO THE NORTH ON
FRIDAY TEMPERING THE HIGHS SOME.

IN THE EXTENDED PERIOD...THE RIDGE BUILDS OVER THE TEXAS AREA FRIDAY
INTO SATURDAY WITH DECENT RIDGING UP INTO OUR AREA BEFORE SHIFTING
OFF TO THE EAST SOME AS OUR GULF OF ALASKA UPPER LOW OPENS UP AND
MOVES INLAND. MODELS HAVE BEEN STRUGGLING WITH THIS EVOLUTION...
ESPECIALLY IN REGARDS TO HOW MUCH SPLITTING THERE WOULD BE. GFS AND
ECMWF ARE MORE IN STEP WITH LESS SPLITTING WITH THIS WEEKEND SYSTEM
ON THEIR 12Z RUNS. MODELS TO A VARYING DEGREE ARE ALSO TRENDING
TOWARD A SECONDARY COLD SHORTWAVE FOLLOWING QUICKLY BEHIND THIS
SYSTEM SUNDAY NIGHT EXCEPT FOR THE GEM WHICH IS SLOWER AND HOLDS OFF
UNTIL MONDAY. COULD BE ENOUGH COLD AIR FOR A SHORT PERIOD OF LIGHT
SNOW IN CENTRAL WYO SUNDAY NIGHT OR EARLY MONDAY...ESPECIALLY WHERE
IT PRECIPITATES. WILL WATCH THIS CLOSELY OVER THE NEXT COUPLE DAYS.
AFTER THAT...FLAT RIDGE REBUILDS MONDAY NIGHT INTO TUESDAY FOR
REBOUNDING TEMPERATURES.


&&

.AVIATION.../06Z ISSUANCE/

AN AREA OF ISOLATED -SHRA ONGOING...ALONG AND SE OF A KRKS-KCPR
LINE...WILL GRADUALLY SHIFT EAST OF THE AREA BY 09Z. EXCEPT FOR VERY
BRIEF MVFR CONDITIONS IN -SHRA ACTIVITY...VFR CONDITIONS WILL
PREVAIL IN THIS AREA. ACROSS FAR NORTHWEST WYOMING LOW CLOUDS AND
SOME SNOW SHOWER ACTIVITY WILL BE POSSIBLE FOR THE REST OF THE
NIGHT. THE SNOW SHOWER ACTIVITY IS EXPECTED TO DECREASE TO ONLY SOME
FLURRIES BY 12Z. BETWEEN 12Z AND 18Z THE MAIN CONCERN WILL BE LOW
CLOUDS /020-050 KFT AGL/ AND POSSIBLY SOME PATCHY FOG ACROSS
NORTHWEST WYOMING /NW OF A KAFO-KPNA-30W KCOD LINE/. THIS WOULD
PRIMARILY IMPACT THE KJAC TERMINAL...WITH CEILINGS AT KJAC PROBABLY
HIGH MVFR TO LOW VFR. FOG CHANCES AT KJAC WILL BE SLIM DUE TO THE
AFOREMENTIONED STRATCU DECK. THIS FOG/LOW CLOUDS ACROSS THE
NORTHWEST ARE EXPECTED TO ERODE BY AROUND 18Z. OTHERWISE...VFR
CONDITIONS WILL OCCUR FOR THE REST OF TONIGHT WITH SKC CONDITIONS
AND BREEZY WINDS BECOMING LIGHTER AS THE NIGHT PROGRESSES WITH
MAINLY LIGHT WIND DURING THE DAY WEDNESDAY.  AFTER 00Z...EXPECT
INCREASING MID/HIGH LEVEL CLOUDINESS AND STRENGTHENING MOUNTAIN TOP
WINDS WITH POSSIBLY SOME LLWS ON THE LEE SIDE OF MOUNTAIN RANGES
ALONG THE CONTINENTAL DIVIDE DEVELOPING AFTER 06Z THURSDAY.

&&

.FIRE WEATHER...

WINDY CONDITIONS ARE EXPECTED FOR THE REST OF THE AFTERNOON AND
EARLY EVENING. DOWNSLOPING WINDS WILL LIMIT CHANCES FOR WETTING
RAIN EAST...WHILE MORE FAVORABLE FLOW WILL MAXIMIZE POTENTIAL
ALONG WEST FACING SLOPES ALONG AND WEST OF THE DIVIDE...ESPECIALLY
NORTHWEST WYOMING THROUGH THIS EVENING. A COLD FRONT SWEEPS THROUGH
TONIGHT...CHANGING THE WIND DIRECTION TO MORE WESTERLY EVERYWHERE.
THE WIND AND THE RAIN WILL CLEAR OUT ON WEDNESDAY WITH COOL
TEMPERATURES REMAINING. TEMPERATURES REBOUND A BIT ON THURSDAY AS
HIGH PRESSURE BUILDS IN FROM THE SOUTH BUT IT WILL BE ANOTHER BREEZY
DAY IN SPOTS WITH SOUTHWEST WINDS OF 15 TO 25 MPH COMMON BETWEEN
ROCK SPRINGS AND CASPER AND OVER THE HIGHER ELEVATIONS.

&&

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

&&

$$

SHORT TERM...LIPSON
LONG TERM...SKRBAC
AVIATION...WM
FIRE WEATHER...LIPSON








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