Area Forecast Discussion
Issued by NWS Riverton, WY

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941
FXUS65 KRIW 090905
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
205 AM MST TUE FEB 9 2016

.SHORT TERM...TODAY THROUGH THURSDAY NIGHT

TEMPERATURE INVERSIONS ARE BECOMING RATHER STARK. FOR EXAMPLE...HERE
IN OUR COZY PROTECTED WIND RIVER BASIN WE ARE SITTING AT 28DEGREES
HERE ATOP GRIFFEY HILL AT THE NWS LOCATION...WHILE IT IS 22
DEGREES AT THE NEARBY RIW ASOS SITE...AND ONLY 1 ABOVE RIGHT ALONG
THE LITTLE WIND RIVER 2 MILES SOUTH OF RIVERTON AT THE TIME OF
THIS WRITING. ABOVE THE INVERSION...BOTH CROWHEART AND DUBOIS HAVE
36 DEGREES WITH NW WINDS OF 29 GUST 37 MPH IN DUBOIS IN THE UPPER
WIND RIVER BASIN AS THE NW GRADIENT WIND ALONG THE FRONT OF THE
BUILDING RIDGE CONTINUES TO MIX OUT AREAS ABOVE THE INVERSIONS.
THESE TEMPERATURE INVERSIONS WILL BE A PLAYER THROUGH AT LEAST
THURSDAY MORNING. BY WEDNESDAY...700MB TEMPS WILL RISE TO 4C OVER
CENTRAL WY AS THE STRONG RIDGE TO THE WEST ATTEMPTS TO BUILD INTO
THE AREA. BY WEDNESDAY...WE WILL WITNESS NEAR RECORD HIGHS IN THE
50S AND EVEN SOME LOW 60S IN AREAS LIKE THE CODY FOOTHILLS AS WELL
AS JOHNSON COUNTY INCLUDING BYG. OTHER AREAS THAT MIX OUT SUCH AS
THE SOUTHERN WIND CORRIDOR FROM THE RED DESERT TO CPR WILL NOT GET
AS WARM AS THERE IS STILL PLENTY OF SNOW COVER TO MELT DOWN IN
THOSE AREAS SO 40S ARE MORE LIKELY IN THOSE AREAS WED. THE TRAPPED
BASINS AND VALLEYS WILL REMAIN IN THE UPPER 30S TO THE MID 40S. BY
WEDNESDAY...THE RIDGE WILL FLATTEN A BIT ALLOWING A COUPLE OF WEAK
VORT LOBES TO TRACK SOUTHEAST ACROSS THE AREA. THE SFC GRADIENT
WILL INCREASE AS AN ASCT SFC LOW TRACKS SOUTHEAST ACROSS EASTERN
MT AND THE NORTHERN PLAINS INCREASING THE SFC GRADIENT THAT WILL
PRECEDE A LEE SIDE SFC TROUGH. H7 WINDS WILL INCREASE TO 35 KNOTS
WED. THIS WILL BE THE MECHANICS DRIVING THE INCREASING SOUTHWEST
WIND FROM THE RED DESERT TO CPR ON WEDNESDAY HELPING TO DRAW IN
THE WARMER AIR. IN ADDITION...THE CODY/CLARK AREA WILL EXPERIENCE
INCREASING WEST WINDS WEDNESDAY AS A MARGINAL TEMP GRADIENT
BETWEEN YNP AND THE CODY FTHLS DVLPS ALONG WITH A WEAK MTN WAVE
SIGNATURE. IN ADDITION...THE FROUDE NUMBER FOR 15Z WED IS FCST TO
BE A 1.OO. WESTERLY EXITING WINDS ON THE CROSS SECTION ARE
STRONGER THEN THE WINDS ENTERING THE AREA. FOR NOW WILL HANDLE THE
CLARK/CODY WINDS WITH AN SPS AS HIGH WIND POTENTIAL APPEARS TO BE
BORDERLINE AT THIS TIME. BEHIND THIS WEAK DISTURBANCE WED...A
MAINLY DRY BACKDOOR COOL FRONT WILL LOWER TEMPS ON
THURSDAY...EXCEPT WILL ACTUALLY INCREASE TEMPS IN AREAS STILL
TRAPPED WITHIN STRONG INVERSIONS. ONE SIDE NOTE...PATCHY LATE
NIGHT AND MORNING FOG WILL LIKELY FORM IN THE WESTERN VALLEYS AND
BASINS AS WELL AS IN THE WIND RIVER BASIN TONIGHT THROUGH THURSDAY
MORNING ALONG WITH FAVORABLE SOUNDINGS INDICATING DRY AND MILD AIR
ATOP STRONG MOIST COLD AIR...ESPECIALLY ON TUE/WED MORNINGS. A FEW
SNOW FLURRIES ARE EXPECTED IN THE NW MTNS AND IN THE BIG HORNS
BEHIND THE BACKDOOR COOL FRONT THU NT.

.LONG TERM...FRIDAY THROUGH TUESDAY
MEAN LONGWAVE RIDGE HOLDS OVER THE WESTERN U.S. THROUGH THE
WEEKEND BEFORE THE FLOW WILL LIKELY FLATTEN. MODELS ARE STILL
SHOWING A SHORTWAVE MOVING THROUGH THE RIDGE. BOTH THE GFS AND
EURO SEEM RATHER STRONG FOR A SYSTEM ENTERING A STRONG RIDGE. THE
GEM IS FURTHER NORTH WITH JUST A GLANCING BLOW OF PCPN TO THE FAR
NORTH. THE GFS IS ALSO ON THE SLOW END WITH THE EURO ON THE FAST
END. POPS ARE LOW NOW FOR THE MTNS AND FAR NORTH SO NOT A BIG DEAL
BUT LEAN TOWARDS A WEAKER SYSTEM THAN THE GFS/EURO ARE SHOWING.
SOME INCREASE IN WIND PROBABLY WITH SOME INVERSIONS WEAKENING OR
BREAKING BUT LIMITED PCPN CHANCES AND MAINLY OVER THE MTNS/FAR
NORTH. AFTER THAT...AS THE EXPECTED FLOW FLATTENS...WE`LL SEE MORE
WIND IN THE MTNS/FOOTHILLS AND WIND CORRIDOR WITH MORE UPGLIDE
PCPN ACROSS THE WEST. TEMPS COULD BE WARM ENOUGH TO GET SOME MIXED
PCPN OR EVEN VALLEY RAIN BY THEN...SO SOMETHING TO WATCH WITH
TIME. INCREASED GRADIENT AND WINDS ALOFT WILL HELP MIX THE BASINS
AND VALLEYS ALSO.

&&

.AVIATION.../12Z ISSUANCE/

THERE IS A GOOD SHOT AT WIDESPREAD FOG/LOW CLOUDS DEVELOPING BETWEEN
09Z AND 14Z OVER THE FAR WESTERN VALLEYS...INCLUDING THE JAC
TERMINAL. IF IT DEVELOPS...FOG/LOW CEILINGS WILL LIKELY PERSIST
THROUGH THE MORNING DUE TO THE VERY STEEP SURFACE INVERSION...NOT
IMPROVING UNTIL EARLY TO MID AFTERNOON. PATCHY FOG WILL ALSO BE
POSSIBLE IN THE CENTRAL BASIN...BUT COVERAGE SHOULD BE LIMITED AND
ONLY HAVE VCFG AT KRIW TERMINAL. OTHERWISE...VFR CONDITIONS WITH
ONLY VARIABLE HIGH LEVEL CLOUDS ARE EXPECTED. BREEZY WEST TO
NORTHWEST WIND ARE EXPECTED IN THE DUBOIS AND CASPER AREAS...AS WELL
AS IN THE MOUNTAINS...CREATING MOUNTAIN TURBULENCE AND POCKETS OF
LOW LEVEL WIND SHEAR. TONIGHT...FOG DEVELOPMENT IS AGAIN
POSSIBLE...MAINLY OVER THE FAR WESTERN VALLEYS...BUT WILL ONLY HAVE
VCFG AND SEE WHAT ENDS UP HAPPENING THIS MORNING. ALSO...TONIGHT
SOME STRONG WINDS ARE EXPECTED TO DEVELOP OVER THE CODY FOOTHILLS
WHICH WILL RESULT IN BREEZY WESTERLY WINDS OR LOW LEVEL WIND SHEAR
AFTER 06Z WEDNESDAY.

&&

.FIRE WEATHER...

FIRE DANGER REMAINS LOW ACROSS THE FORECAST AREA THROUGH THE WORK
WEEK...WITH MILD TEMPERATURES ABOVE THE TEMPERATURE INVERSIONS AND
SNOW COVERING MANY SURFACES. WINDS...HOWEVER...WILL BE ON THE BREEZY
SIDE TODAY ACROSS THE USUAL WIND PRONE AREA OF CENTRAL WYOMING.
WEDNESDAY...AREAS IN AND ADJACENT TO THE ABSAROKA MOUNTAINS COULD
SEE NEAR HIGH WIND CRITERIA. IT WILL BE FAIRLY WINDY FROM THE RED
DESERT TO CASPER WEDNESDAY AS WELL. OTHERWISE...MOST LATE MORNINGS
AND AFTERNOONS ACROSS WYOMING SHOULD SEE GOOD SMOKE DISPERSION
THROUGH THE END OF THE WEEK.

&&

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

&&

$$

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



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