Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 212050
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
250 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.../00Z ISSUANCE/
SHORTWAVE APPROACHING SOUTHWEST IDAHO WILL SWING ACROSS NORTHWEST
WYOMING TODAY. CLOUD COVER...SHOWERS AND ISOLATED THUNDERSTORMS WILL
BE ON THE DECREASE THROUGH 00Z TODAY ACROSS WEST CENTRAL AND
SOUTHWEST WY INCLUDING KJAC AND KAFO AS BEST FORCING AND JET ENERGY
PUSH ACROSS WYOMING. HOWEVER...EAST OF THE DIVIDE...SCATTERED
THUNDERSTORMS CAN BE EXPECTED ACROSS HOT SPRINGS AND FREMONT
COUNTIES ALONG WITH 40 TO 50 MPH WINDS...INCLUDING KRIW AND KLND
THROUGH 22Z. HOWEVER...MAINLY SNOW SHOWERS WILL CONTINUE ACROSS
NORTHWEST WY INCLUDING YELLOWSTONE PARK AS SNOW LEVELS DROP TO
6500 FEET THROUGH THIS EVENING AS MOISTURE WRAPS AROUND THE
CIRCULATION NOW OVER IDAHO THAT WILL TRACK TO MT. MOUNTAIN TOP
OBSCURATIONS WILL BE WIDESPREAD THROUGH ABOUT 21Z-23Z BEFORE
TROUGH AND ASSOCIATED COLD FRONT SWING EAST OF KJAC BUT WILL
LINGER THROUGH 06Z AT YNP. CANNOT RULE OUT A BRIEF PERIOD OF MVFR
AT KJAC WITH A HEAVIER RAIN SHOWER THROUGH 21Z TODAY.
OTHERWISE...KJAC WILL REMAIN VFR WITH RAPID CLEARING BETWEEN
23Z/TODAY AND 02Z/WED. OTHER TERMINALS WILL ALL BE VFR THROUGH THE
PERIOD. EXPECT ENOUGH INSTABILITY AND MOISTURE TO GENERATE
CONVECTION ACROSS SOUTHWEST WYOMING...AFFECTING THE KRKS TERMINAL
THROUGH 22Z OR SO. MUCH MORE ISOLATED CONVECTION ELSEWHERE.
LARGER ISSUE EAST OF THE DIVIDE WILL BE DOWNSLOPE WINDS NEAR THE
MOUNTAINS AND FOOTHILLS AND GUSTY SOUTH TO WEST SURFACE WIND.
WINDS WILL BE 15-20KTS WITH GUSTS 25-35KTS. STRONGEST NON
THUNDERSTORM WINDS WILL BE THROUGH 23Z THIS AFTERNOON AT KCPR
WHERE 25G35KTS IS LIKELY. TROUGH PASSAGE BETWEEN 00Z- 06Z/WED WILL
VEER WINDS TO THE NORTHWEST WITH DECREASING SPEEDS AFTER SUNSET.
THE EXCEPTION WILL BE KRIW WHERE FAVORABLE NORTHWEST WIND OF
15-25KTS IS LIKELY THROUGH ABOUT 06Z/WED. ALL TERMINALS WILL SEE
RAPID CLEARING FROM THE WEST BEGINNING AT 00Z/WED AND CONTINUING
THROUGH 06Z/WED.

&&

.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...LIPSON
FIRE WEATHER...LIPSON





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