Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 160935
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
235 AM MST TUE DEC 16 2014

.SHORT TERM...TUESDAY THROUGH THURSDAY NIGHT

THERE ARE TWO MAIN CONCERNS WITH THE WEATHER TODAY. THE FIRST IS
MAINLY EAST OF THE DIVIDE. WITH THE SNOW OVER THE WEEKEND AND SOME
MELTING TODAY...WE HAVE SEEN THE RETURN OF THE FOG MONSTER TO
PORTIONS OF THE AREA. THE MAIN AREAS AT THIS TIME LOOK TO BE JOHNSON
COUNTY...THE BIG HORN BASIN AS WELL AS PORTIONS OF THE WIND RIVE
BASIN. MAINLY...AREAS WHERE WINDS ARE LIGHT AND THE MOST SNOW FELL
OVER THE PAST FEW DAYS. CONTINUITY HAD SOME FOG IN THE FORECAST
THROUGH 8 AM AND AT THIS POINT THIS LOOKS REASONABLE.
MEANWHILE...THE POCATELLO RADAR SHOWS A BATCH OF SHOWERS MOVING
NORTH AND NORTHEASTWARD WITH SOME WARM ADVECTION. MODELS AT THIS
POINT ARE NOT HANDLING THIS VERY WELL. AT THIS POINT...SOME SNOW
LOOKS LIKE A DECENT POSSIBILITY FOR THE WEST...ESPECIALLY THE WEST.
HOWEVER...THERE IS NOT A LOT OF MOISTURE OR DYNAMICS TO WORK WITH.
THE GFS HAS RAISED ITS QPF AMOUNTS HOWEVER. AS A RESULT...WE KEPT
AMOUNTS BELOW ADVISORY LEVEL BUT DID RAISE THEM A BIT ACROSS THE
FAVORED WESTERLY SLOPES. OTHERWISE...EXPECT A MOSTLY CLOUDY DAY WITH
COOL TEMPERATURES BUT NOT TOO FAR OFF OF SEASONAL NORMALS.

BY WEDNESDAY THE REGION SHOULD BE IN BETWEEN SYSTEMS WITH WESTERLY
FLOW PREDOMINATING ACROSS THE AREA. SOME OROGRAPHIC SNOW SHOWERS
WILL CONTINUE ACROSS THE WEST BUT AMOUNTS THIS DAY SHOULD BE FAIRLY
LIGHT. MEANWHILE...EAST OF THE MOUNTAINS IT LOOKS DRY WITH FAIRLY
SEASONABLE TEMPERATURES FOR MANY AREAS. THE EXCEPTIONS MAY BE THE
DEEPER BASINS WHERE INVERSIONS WILL BE HARD TO BREAK DUE TO
SNOWPACK...LITTLE WIND AND THE WEAKEST SUN OF THE YEAR AS WE
APPROACH THE WINTER SOLSTICE. AS A RESULT...WE KEPT THOSE AREAS
COOLER AND BELOW NUMBERS. ANOTHER SHORTWAVE WILL APPROACH THE AREA
FOR THURSDAY WITH ANOTHER CHANCE OF SNOW FOR THE WEST. AS FOR THE
POSSIBILITY OF IT JUMPING THE DIVIDE...WE LEFT IN A SLIGHT CHANCE
FOR THE EVENING ALTHOUGH NONE OF THE MODELS SHOW IT AT THIS POINT.
BUT...WE WOULD PREFER TO WAIT ANOTHER COUPLE OF RUNS BEFORE REMOVING
IT. TEMPERATURES ONCE AGAIN SHOULD BE FAIRLY CLOSE TO NORMAL FOR
MOST LOCATIONS.

.LONG TERM...FRIDAY THROUGH TUESDAY

HARD NOT TO FOCUS ON THE POTENTIAL CHANGES BEYOND THIS PERIOD BUT
THAT WILL JUST HAVE TO WAIT AT ANOTHER DAY. WEAK SHORTWAVE RIDGE
MOVES ACROSS THE CWFA FRIDAY INTO FRIDAY NIGHT WITH WEAK ISENTROPIC
UPGLIDE INTO THE WRN MTNS WHICH MAY BE JUST ENOUGH FOR A LITTLE
LIGHT SNOW OR FLURRIES. DRY ELSEWHERE. BOTH THE ECMWF AND GFS THEN
HAVE A WEAK RIPPLE IN THE GENERAL WLY FLOW ON SATURDAY WHICH STILL
SHOWS UP AS A WARM ADVECTION/UPGLIDE PATTERN OUT WEST WITH WEAK FLOW
AND LIMITED MOISTURE. ENOUGH FOR SOME LIGHT SNOW OR FLURRIES BUT
DOESN`T LOOK SIGNIFICANT BY ANY STRETCH. BY SUNDAY...NW FLOW STARTS
TO STRENGTHEN IN RESPONSE TO BUILDING RIDGE ALONG AND JUST OFF THE
WEST COAST AS DEEP...COLD TROUGH MOVES INTO THE GULF OF ALASKA/ERN
PACIFIC. THIS COLD TROUGH IS CURRENTLY OVER ERN ASIA AND MAY PORTEND
SIGNIFICANT CHANGES THE MIDDLE OF NEXT WEEK BUT IN THE MEANTIME...IT
PUSHES A STRONG JET INTO THE WEST COAST WHICH MAY AID IN STRONG TO
HIGH WINDS IN THE ABSAROKAS/CODY FOOTHILLS SUNDAY NIGHT INTO MONDAY
MORNING. THE STRONG NW FLOW LOOKS TO BE A MUCH BETTER...MOIST...
UPGLIDE PATTERN FOR THE WEST WITH AT LEAST THE POTENTIAL FOR
SIGNIFICANT MOUNTAIN SNOWFALL. A LEAD PIECE OF OUR ERN PACIFIC
TROUGH IS EXPECTED TO MOVE OVER THE BUILDING RIDGE AND MOVE SE
ACROSS AT LEAST OUR NERN ZONES WITH FRONTAL BOUNDARY DROPPING INTO
THE NRN ZONES AND POTENTIALLY BEING OVERRUN BY MOISTURE IN THE NW
FLOW. A CHANCE OF SNOW FOR AT LEAST THE NRN AND NERN ZONES LOOKS
GOOD AND POTENTIALLY DOWN TO NEAR CPR OR AT LEAST DOWNWIND OF THE
BIGHORNS IN FAVORABLE NW FLOW. ECMWF HAS ANOTHER SIMILAR SEWD MOVING
SHORTWAVE FOR TUESDAY THAT THE GFS HAS SHIFTED SLIGHTLY EWD. HIGHER
POPS IN THE MTNS WITH AT LEAST 20-30 POPS IN THE NORTH AND EAST OK
FOR NOW BUT WE MAY NEED MORE WITH TIME AGAIN.

&&

.AVIATION.../12Z ISSUANCE/

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

AREAS OF LOW CLOUDS AND FOG WILL OCCUR THROUGH 15Z WITH MVFR TO IFR
CONDITIONS. AFTER 15Z VFR CONDITIONS WILL PREVAIL OVER THE REGION.
SOME LIGHT SNOW WILL OCCUR OVER THE ABSAROKA AND WIND RIVER
MOUNTAINS AFTER 09Z AND CONTINUE OFF AND ON THROUGH 06Z WED. EXPECT
MOUNTAINS TO BE OBSCURED FROM TIME TO TIME WITH MVFR/IFR CONDITIONS.
ISOLATED SNOW SHOWERS ARE POSSIBLE OVER THE LOWER ELEVATIONS AFTER
12Z THROUGH 06Z WED.

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

SNOW SHOWERS WILL OCCUR IN THE WESTERN MOUNTAINS THROUGH MUCH OF THE
PERIOD. SNOW SHOWERS WILL OCCUR AT TIMES IN THE WESTERN VALLEYS
THROUGH 06Z WED. EXPECT AREAS OF MVFR CONDITIONS THROUGH 06Z
WED WITH LOCAL IFR. MOUNTAINS WILL BE FREQUENTLY OBSCURED. PLEASE
SEE INDIVIDUAL TERMINAL FORECASTS FOR DETAILS.
&&

.FIRE WEATHER...

RELATIVE HUMIDITY VALUES WILL REMAIN ELEVATED FOR SEVERAL DAYS OVER
THE SNOWPACK. AS A RESULT FIRE DANGER WILL REMAIN LOW THROUGH THIS
PERIOD. WITH ONLY LIGHT WINDS EXPECTED MIXING HEIGHTS ARE EXPECTED
TO REMAIN LOW AND SMOKE DISPERSION IS EXPECTED TO BE
POOR...ESPECIALLY IN BASINS AND DEEPER VALLEYS WHERE INVERSIONS MAY
PERSIST THROUGH THE DAY.
&&

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

&&

$$

SHORT TERM...HATTINGS
LONG TERM...PS
AVIATION...AR
FIRE WEATHER...HATTINGS








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