Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 281710
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1010 AM MST FRI NOV 28 2014

.SHORT TERM...FRIDAY THROUGH SUNDAY NIGHT

WE HAVE TWO CONCERNS WITH THE FORECAST OVER THE SHORT TERM...WIND
AND SNOW. THE FIRST FOCUS IS WIND. HIGH WINDS ARE ONGOING THE
ABSAROKAS AND THE CODY FOOTHILLS...INCLUDING NUMEROUS GUSTS PAST 80
MPH AT CHIEF JOSEPH. THIS WARNING STILL LOOKS PRETTY GOOD SO WE WILL
CONTINUE IT AS IS. THE QUESTION IS WHAT TO DO ELSEWHERE. A HIGH WIND
WATCH WAS ISSUED FOR THE LANDER FOOTHILLS WITH POSSIBLE MOUNTAIN
WAVE DEVELOPMENT LATER TODAY AND TONIGHT. IN ADDITION...STRONG WINDS
AT 700 MILLIBARS ARE EXPECTED TO CLIMB TO 60 TO 70 KNOTS TONIGHT
ACROSS THIS AREA. WITH THIS WE HAVE ISSUED A HIGH WIND WATCH FOR THE
GREEN AND RATTLESNAKE RANGE AS WELL. WE ALSO TOSSED AROUND THE IDEA
FOR THE REMAINDER OF NATRONA COUNTY BUT DECIDED TO HOLD OFF FOR NOW.
A PLACE LIKE OUTER DRIVE MAY SEE AN ISOLATED GUST OVER 55 MPH...BUT
NOT IN MOST OF THE AREA. SO...WE WILL CONTINUE THE SPECIAL WEATHER
STATEMENT FOR THIS AREA. IT MAY BE A DIFFERENT STORY FOR SATURDAY
THOUGH. THE OTHER STORY TODAY WILL BE THE MILD TEMPERATURES. THE GFS
AGAIN IS VERY WARM WITH HIGHS IN THE 70S TODAY FOR LANDER AND
RIVERTON. WE AGAIN THINK THIS IS TOO WARM. HOWEVER...60 IS CERTAINLY
NOT OUT OF THE REALM OF POSSIBILITY. IN ADDITION...OTHER THAN A FEW
FLURRIES ACROSS FAR NORTHERN WYOMING...MOST AREAS SHOULD BE DRY
TODAY.

THE FOUR LETTER WHITE STUFF...AKA SNOW...WILL RE-ENTER THE FORECAST
STARTING ACROSS THE WEST STARTING LATER TONIGHT. SNOW SHOULD BREAK
OUT LATER AT NIGHT AS MOISTURE AND SOME ADDITIONAL DYNAMICS FROM THE
LEFT FRONT QUADRANT OF AN 120 KNOT JET MAX ARRIVE. PERIODS OF SNOW
WILL CONTINUE THROUGH THE DAY ON SATURDAY...ENHANCED BY DECENT UPPER
LEVEL DYNAMICS FIRST WITH THE AFOREMENTIONED LEFT FRONT QUAD OF A
JET MAX. THEN IN THE AFTERNOON BY THE RIGHT REAR QUAD OF ANOTHER MAX
MOVING ACROSS MONTANA. THE BEST ACCUMULATIONS APPEAR TO BE WELL
REPRESENTED BY THE WATCHES AND THESE WILL BE CONTINUED AS IS.
ELSEWHERE IN THE WEST...THERE WILL BE SNOW BUT WITH THE BEST
DYNAMICS FURTHER AWAY AND THIS SYSTEM NOT AS WET AS THE PREVIOUS ONE
ADVISORIES WOULD PROBABLY BE SUFFICIENT.

MEANWHILE...EAST OF THE DIVIDE THE STORY WILL BE WIND ON SATURDAY.
WINDS ALOFT WILL STILL BE RATHER STRONG IN THE 50 TO 60 KNOT RANGE.
IN ADDITION...A COLD FRONT DROPPING SOUTHWARD WILL TIGHTEN THE
PRESSURE GRADIENT AND AID IN DOWNWARD MOMENTUM. PLACES LIKE NATRONA
COUNTY AND POSSIBLY EASTERN SWEETWATER COUNTY COULD NEED A WATCH
SOMETIME TODAY. THIS LOOKS TO BE ANOTHER MILD DAY. MOS
NUMBERS...ESPECIALLY IN CENTRAL AND SOUTHERN AREAS MAY BE TOO LOW
WITH STRONG DOWNSLOPING FLOW. AS A RESULT...WE KEPT THEM ABOVE
NUMBERS. THE COLD FRONT WILL BEGIN TO SLIDE INTO THE STATE TOWARD
DARK...BUT AT THIS TIME STRONG DOWNSLOPING FLOW SHOULD KEEP THINGS
DRY.

THE FRONT THEN DROPS SOUTHWARD ACROSS THE STATE ON SATURDAY NIGHT.
AT THIS TIME...IT APPEARS THERE IS NOT MUCH MOISTURE TO WORK WITH.
THE AREA BETWEEN THE ABSAROKAS AND BIG HORN RANGE WILL LIKELY HAVE
STRONG DOWNSLOPING FLOW AND MAY SEE LITTLE SNOW AT ALL. BOTH THE NAM
AND GFS SHOW A BIT MORE EAST OF THE BIG HORN RANGE BUT EVEN HERE IT
LOOKS TO BE SUB ADVISORY. THE BEST CHANCE OF ANY SNOW WOULD BE LATER
SATURDAY NIGHT INTO SUNDAY MORNING.

THE FRONT THEN SINKS INTO SOUTHERN WYOMING BY SUNDAY AFTERNOON. MUCH
COLDER AIR WILL THEN MOVE IN WITH HIGH TEMPERATURES 30 TO 40 DEGREES
COLDER THAN ON FRIDAY. THIS COLD AIR IS NOT AS COLD AS THE ARCTIC
BLAST EARLIER THIS MONTH...BUT IT WILL BE A SLAP TO THE FACE. THERE
IS THE RISK FOR A LONGER PERIOD OF SNOW ACROSS SWEETWATER COUNTY
HOWEVER AS THE FRONT STALLS THERE AND MAYBE ENHANCED A BIT BY SOME
UPPER LEVEL DYNAMICS. STAY TUNED. ELSEWHERE...THE SNOW SHOULD END
FROM NORTH TO SOUTH ON SUNDAY AS THE FRONT DROPS SOUTHWARD AND SHUTS
OFF THE MOISTURE.

.LONG TERM...MONDAY THROUGH FRIDAY

THE KEY WEATHER PLAYERS AT THE BEGINNING OF THE EXTENDED WILL BE A
SHORTWAVE TROUGH OVER BRITISH COLUMBIA...A STRONG UPPER LOW OVER THE
EASTERN PACIFIC NEAR 35 NORTH...135 WEST...AND AN ARCTIC AIR MASS
ALONG AND EAST OF THE DIVIDE.

THE SHORTWAVE TROUGH OVER BRITISH COLUMBIA WILL SWING ACROSS THE
EXTREME NORTHERN ROCKIES MONDAY NIGHT/TUESDAY. THIS WILL RESULT IN A
LEE TROUGH DEVELOPING MONDAY WHICH SHOULD ERODE THE ARCTIC AIR MASS
IN MIXED AREAS...BUT CONCERNED TRAPPED BASINS COULD SEE ANOTHER
BITTER COLD DAY. THIS IS MOST LIKELY TO OCCUR OVER THE EASTERN BIG
HORN BASIN...WITH A CLOSE SECOND BEING THE CENTRAL/NORTHERN WIND
RIVER BASIN. HAVE CONTINUED TO GO WELL UNDER MEX MOS GUIDANCE BY 10
TO 20 DEGREES IN THOSE AREAS. THE TRACK OF THIS STORM SYSTEM IS
FARTHER NORTH THAN THE ONE OCCURRING THIS WEEKEND. THUS MUCH OF THE
IMPACT WITH THIS SYSTEM WILL REMAIN OVER THE NORTHWEST IN THE MOIST
WESTERLY FLOW AHEAD OF THE TROUGH LATE MONDAY INTO MONDAY NIGHT.
SNOW AMOUNTS AND WIND WILL BE LESS/WEAKER WITH THIS SYSTEM...BUT NOT
OUT OF THE QUESTION SOME WINTER ADVISORIES MIGHT BE NEEDED OVER
THE FAR WEST/NORTHWEST...AS WELL AS HIGH WIND HIGHLIGHTS OVER
ABSAROKA MTS/CODY FOOTHILLS AND IN THE SOUTH PASS TO CASPER WIND
CORRIDOR AREA.

A RELATIVELY QUIET PERIOD IS EXPECTED TUESDAY AFTERNOON AND TUESDAY
NIGHT IN WAKE OF THE SYSTEM MONDAY NIGHT...WITH ONLY A SLIGHT CHANCE
OF SOME LIGHT SNOWFALL OVER THE WESTERN MOUNTAINS.

THE FOCUS WILL THEN TURN TO THE PROGRESSION OF THE AFOREMENTIONED
UPPER LOW IN THE EASTERN PACIFIC. GLOBAL MODELS CONTINUE TO STRUGGLE
WITH THE EVOLUTION OF THIS SYSTEM AS IT PUSHES ACROSS THE WEST
DURING THE MIDDLE OF NEXT WEEK. SOME MODEL SOLUTIONS RESULT IN A
RIDGE DEVELOPING OVER THE AREA WITH MAINLY DRY CONDITIONS WITH THE
UPPER LOW OPENING UP AND SHIFTING NORTHEAST ACROSS THE PACIFIC
NORTHWEST. ON THE OTHER HAND...THE MAJORITY OF MODEL SOLUTIONS ARE
TRENDING TOWARDS THE STRONG UPPER LOW...SHIFTING INTO THE WEST
COAST TUESDAY NIGHT/WEDNESDAY TIME FRAME...AND QUICKLY WEAKENING
AND BECOMING AN OPEN WAVE PUSHING ACROSS THE ROCKIES IN THE
WEDNESDAY NIGHT/THURSDAY TIME FRAME. THE GFS SHOWS SOME ENERGY
OVERSPREADING THE AREA WEDNESDAY AHEAD OF THE MAIN ENERGY. DUE TO
THE UNCERTAINTY WILL CONTINUE TO HAVE RELATIVELY LOW POPS WITH AN
EMPHASIS ACROSS THE WEST...ONLY SPREADING POPS EAST OF THE DIVIDE
WED NIGHT/THURSDAY. THE PACIFIC NATURE OF SYSTEM WILL RESULT IN
SEASONAL TO ABOVE AVERAGE TEMPERATURES...BUT STILL LOOKS LIKE
MAINLY SNOW EVEN IN WESTERN VALLEYS...WHILE LOWER ELEVATIONS EAST
OF THE DIVIDE WOULD SUPPORT MORE RAIN/SNOW OR ALL RAIN.

IF CURRENT TIMING OF THIS SYSTEM WED/THUR IS CORRECT...A RELATIVELY
QUIET DAY IS EXPECTED FRIDAY...BUT AGAIN CANNOT RULE OUT SOME LIGHT
SNOW/FLURRIES OVER THE WESTERN MOUNTAINS IN THE MODEST WESTERLY FLOW
EXPECTED.

&&

.AVIATION.../12Z ISSUANCE/

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

THE MAIN HAZARD THROUGH THE PERIOD WILL BE LLWS ACROSS THE AREA WITH
VFR CONDITIONS PREVAILING THROUGH 18Z SATURDAY.

STRONG WEST TO SOUTHWEST WIND AT 50-60KT AT FL080-100 WILL CONTINUE
TO CAUSE AREAS OF LLWS AND MDT-SVR TURBULENCE ACROSS THE AREA
THROUGH  TONIGHT.  MOUNTAIN WAVE ACTIVITY WITH SOME OF THESE
STRONGER WINDS MIXING DOWN THE EAST SLOPES OF THE DIVIDE WILL
PRODUCE VERY STRONG ERRATIC WIND GUSTS OVER 50KTS VCNTY KCOD...WITH
THESE STRONGER WINDS SURFACING BELOW 6KFT BECOMING MORE LIKELY VCNTY
KDUB-KLND AFTER 00Z SATURDAY.

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

THE MAIN HAZARD THROUGH THE PERIOD WILL BE LLWS ACROSS THE AREA.
VFR CONDITIONS WILL PREVAIL THROUGH 06Z SATURDAY WITH AREAS OF
MVFR/IFR CONDITIONS SPREADING SOUTH 07Z-12Z SATURDAY.

STRONG WEST WIND AT 50-60KT AT FL080-100 WILL CONTINUE TO CAUSE
AREAS OF LLWS AND MDT-SVR TURBULENCE ACROSS THE AREA THROUGH
TONIGHT.  OCNL HIGHER MTN OBSCURATIONS IN -SN WILL CONTINUE VCNTY
AND NORTH OF A KJAC-KCOD LINE THROUGH 00Z SATURDAY...AND THEN MTS
ABOVE 6KFT WILL BECOME MOSTLY OBSCURED IN -SN BY 12Z SATURDAY WITH
AREAS OF IFR/MVFR -SN DEVELOPING OVER THE VALLEYS VCNTY
KJAC-KAFO-KPNA.

&&

.FIRE WEATHER...

OVERALL FIRE DANGER WILL BE LOW...REMAINING LOW THROUGH THE WEEKEND.
TEMPERATURES WILL WARM WARM EAST OF THE DIVIDE AS WEST WINDS AS
SOME DOWNSLOPING INCREASES ACROSS THE AREA. HIGH WINDS WILL BECOME
A THREAT EAST OF THE CONTINENTAL DIVIDE...ESPECIALLY IN THE
ABSAROKA MOUNTAINS AND CODY FOOTHILLS...THROUGH SATURDAY. HIGH
WINDS ARE ALSO POSSIBLE AROUND LANDER AND THE SOUTHWESTERN WIND
CORRIDOR FRIDAY NIGHT INTO SATURDAY. HOWEVER...RELATIVELY
WIDESPREAD SNOW COVER AND COOL TO SEASONAL TEMPERATURES WILL HELP
IN KEEPING MINIMUM RH VALUES WELL ABOVE CRITICAL EVEN WITH THE
WIND. A RETURN TO WINTER EXPECTED THIS WEEKEND AS ANOTHER STORM
BRINGS MORE SNOW TO THE WEST ON SATURDAY...AND POSSIBLY EAST OF
THE DIVIDE SATURDAY NIGHT AND SUNDAY.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WARNING UNTIL 5 PM MST SATURDAY WYZ002-003.

HIGH WIND WATCH FROM THIS AFTERNOON THROUGH SATURDAY MORNING
WYZ018-019.

WINTER STORM WATCH FROM LATE TONIGHT THROUGH SUNDAY MORNING
WYZ001-012-013.

&&

$$

SHORT TERM...HATTINGS
LONG TERM...WM
AVIATION...JB
FIRE WEATHER...HATTINGS









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