Weather Service Report


729 
FXUS65 KRIW 280647
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1144 PM MST THU NOV 27 2014

.SHORT TERM...TONIGHT THROUGH FRIDAY (ISSUED 314 PM MST) 

WV IMAGERY SHOWING CONTINUING RIDGE/TROF PATTERN ACROSS THE CONUS 
FROM WEST TO EAST WITH SPLIT FLOW...TROF OVR THE RIDGE NEAR 
CONFLUENCE OF NWRN US AND BC...COMBINING TO GIVE A STRENGTHENING 
VERY STRONG JET ACROSS THE NWRN STATES...HEADED THIS WAY. 
OTHERWISE...NW FLOW IS IN PLACE ACROSS THE FA WITH SOME MODEST MID 
LVL MOISTURE CONTINUING TO STREAM INTO PORTIONS OF THE WRN FA FROM 
THE EPAC...WITH OROGRAPHIC CLOUD AND SOME LIGHT SNOW FALLING. AT THE 
SFC...A LEE TROF/STATIONARY FRONT IS FORMING AND HANGING ABOUT FROM 
CNTRL MT...THRU ERN WY AND INTO ERN CO.       

TODAY THRU FRI...NW FLOW CONTINUES BUT BEGINS TO FLATTEN AND SAG SWD 
IN RESPONSE TO THE APPROACH OF THE JET AND SW TROF OFF BC COAST. THE 
MAIN EVENT THRU THE END OF THE FCST PERIOD WILL BE THE INCREASING 
WINDS...PARTICULARLY OVR THE ABSAROKAS AND ADJACENT CODY FOOTHILLS 
WHERE HIGH WIND WARNINGS HAVE BEEN POSTED FOR AN EXTENDED PERIOD 
LASTING THRU THE DAY ON SAT. THIS IS IN RESPONSE TO GREATLY 
INCREASING MID/UPR WRLY FLOW NEARLY PERPENDICULAR TO THE MOUNTAIN 
RANGES...WITH EXCELLENT THERMAL AND PRESSURE GRADS DEVELOPING  
ACROSS THE MOUNTAINS AND INTO THE LEE SIDE FOOTHILLS. KCHJ IS 
ALREADY BLOWING 45+G60+ AND HAS BEEN INCREASING ALL MORNING...WHILE 
KCRK IS JUST STARTED TO MIX AND BE AFFECTED WITH 20+G45+ WINDS. 
ADDITIONALLY...MOUNTAIN WAVE PRODUCTION IS PROCEEDING IN EARNEST 
WITH HIGHLY TURBULENT SIGNATURES SHOWING IN ALL SAT IMAGERY. THIS 
WILL HELP TO PIN WINDS CLOSER TO THE SFC. MOUNTAIN WAVES AND WINDS 
EXTENDING INTO THE FOOTHILLS SHOULD START TO REACH MAX LEVELS BY 
FRIDAY MORNING WITH EVEN KCOD REACHING (NEAR) WARNING CRITERIA 
AROUND NOON OR JUST AFTER ON FRIDAY AS DOWNWARD MOMENTUM CONTINUES 
TO CREEP EWD. THE CLARK AREA WILL LIKELY GUST A 100 PLUS KTS THRU 
THIS PERIOD. SOMEWHAT LESSER...BUT STILL BRISK WIND WILL BE FOUND 
ACROSS THE USUAL WIND CORRIDOR FROM SERN FREMONT...ERN SWEETWATER 
AND E THRU NATRONA COUNTIES. FOR AVIATION PURPOSES...LLWS WILL REIGN 
ACROSS MOST OF THE REGION E OF THE DIVIDE IN ADDITION TO THOSE 
REGIONS/AIRPORTS IN MORE OF THE FLATLAND BASINS WEST OF THE 
DIVIDE.   

A MINOR PART OF THIS SET-UP HAS TO DO WITH THE MID LVL MOISTURE 
STREAMING INTO THE REGION FROM THE WEST. THIS WILL ONLY MEAN A 
CONTINUING PRESENCE/CHANCE FOR LIGHT SNOW/FLURRIES ACROSS SOME OF 
THE HIGHER ELEVATION PEAKS OF THE W/NW THROUGH OUT THE PERIOD. IT 
DOES APPEAR...HOWEVER...THERE WILL POSSIBLY BE A DECREASE IN THIS 
ACTION DURING THE DAYTIME ON FRI AS THIS MOISTURE GETS UNDERCUT BY 
A DRY LAY IN ASSOCIATION WITH THE STRONGER FLOW NOSING INTO THE AREA 
AT THIS TIME. INTERESTING BUT NOT TERRIBLY SIGNIFICANT. 

.LONG TERM...FRIDAY NIGHT THROUGH THURSDAY 

PRETTY BUSY IN THE LONG TERM PERIOD...FIRST THERE WILL BE SOME
HEFTY MOUNTAIN WAVE ACTION IN THE WIND RIVER MOUNTAINS THAT WILL
LIKELY COME CRASHING INTO LANDER AND FT WASHAKIE FRIDAY
NIGHT...WHILE STRONG WIND WILL ALSO BE ONGOING IN THE ABSAROKAS
AND CODY FOOTHILLS. SOUTHWEST WINDS WILL ALSO BE HOWLING ACROSS
THE SOUTHERN WIND CORRIDOR FROM ROCK SPRINGS TO CASPER. EVEN
THOUGH WINDS ARE SUPPOSED TO STAY BELOW HIGH WIND CRITERIA...IT
COULD HIT IN A FEW OF THE FAVORED SPOTS AND STRONG CROSS WIND
ALONG INTERSTATES 80 AND 25 WILL MAKE TRAVEL DIFFICULT FOR HIGH
PROFILE VEHICLES AND LIGHT TRAILER TRAFFIC FROM FRIDAY NIGHT
THROUGH EARLY SUNDAY MORNING. 

IN ADDITION TO THE WIND...THERE WILL ALSO BE PERIODS OF HEAVY SNOW
ACROSS THE WESTERN MOUNTAINS WITH OVER A FOOT OF NEW SNOW EXPECTED
OVER THE HIGHER TERRAIN AND UP TO 10 INCHES POSSIBLE IN THE
JACKSON VALLEY...BUT IT WILL BE HARD TO MEASURE GIVEN THE AMOUNT
OF WIND EXPECTED BOTH AT THE VALLEY LEVEL AND IN THE MOUNTAINS.
EXPECT A BLUSTERY DAY ON SATURDAY WITH A LOT OF SNOW AND BLOWING
SNOW THROUGH TETON AND PARK COUNTIES. TRAVEL WILL ALSO BE
DIFFICULT IN THESE AREAS...ESPECIALLY OVER TETON AND TOGWOTEE
PASSES. 

STRONG WIND AND SNOW ARE ALSO EXPECTED IN THE WIND RIVER
MOUNTAINS...HOWEVER...SINCE THE HEAVIER SNOW IS NOT EXPECTED TO
IMPACT NEAR SOUTH PASS...WE DECIDED AGAINST INCLUDING THESE ZONES
IN THE WATCH FOR NOW...BUT IT IS STILL IMPORTANT TO STRESS THAT
TOMORROW THROUGH SUNDAY WILL NOT BE A GOOD TIME TO GO INTO THE
WIND RIVER MOUNTAINS...EXPECT PERIODS OF HEAVY SNOW...WIND GUSTS
OVER 70 MPH AT TIMES AND NEAR BLIZZARD CONDITIONS AT TIMES WEST OF
SOUTH PASS.

SNOW WILL EVENTUALLY SPREAD EAST OF THE DIVIDE AS THE COLD FRONT
ASSOCIATED WITH THIS SYSTEM DROPS SOUTH EARLY SUNDAY MORNING.
MOISTURE WILL BE LIMITED BEHIND THIS FRONT BUT THE SNOW RATIOS
WILL BE A LOT HIGHER SO SOME SPOTS COULD GET AN INCH OF SNOW OUT
OF THE FRONT EAST OF THE DIVIDE.

WE WILL LOSE THE UPPER LEVEL DYNAMICS AND THE MOISTURE BY SUNDAY
EVENING BUT THE RIGHT ENTRANCE REGION OF THE JET ALONG WITH A LOW
TO MID LEVEL CONVERGENCE ZONE MAY KEEP SOME SNOW GOING ACROSS THE
SOUTH INTO SUNDAY AFTERNOON.

MODELS BEGIN TO DIVERGE THEREAFTER WITH SIGNIFICANT DIFFERENCES
AFTER TUESDAY AS THE GFS DIGS A TROUGH TO THE WEST AND BRINGS
WIDESPREAD SNOW BY WEDNESDAY WHILE THE EUROPEAN MODEL BUILDS A DRY
RIDGE INTO THE AREA. FOR THE OFFICIAL FORECAST...STUCK VERY CLOSE
TO CONTINUITY WITH GENEROUS SLIGHT CHANCE POPS AS THERE IS TOO
MUCH UNCERTAINTY TO STICK WITH ANY ONE SOLUTION. 

&&

.AVIATION.../06Z 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 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 FRIDAY 
NIGHT.  MOUNTAIN WAVE ACTIVITY WITH SOME OF THESE STRONGER WINDS 
MIXING DOWN THE EAST SLOPES OF THE DIVIDE WILL PRODUCE 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 08Z-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 FRIDAY 
NIGHT.  OCNL HIGHER MTN OBSCURATIONS IN -SN WILL CONTINUE VCNTY AND 
NORTH OF A KJAC-KCOD LINE THROUGH 00Z SATURDAY...AND THEN MTS ABOVE 
9KFT 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. 
LIGHT SNOW OR FLURRIES WILL LINGER OVER THE HIGHER PEAKS OF THE 
REGION TODAY...PARTICULARLY THE NORTHWEST MOUNTAINS WHILE 
TEMPERATURES 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...FROM TODAY THROUGH THE DAY ON 
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...TO THE EAST OVERNIGHT SATURDAY AND THROUGH SUNDAY 
MORNING. 

&&

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

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

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

&&

$$

SHORT TERM...BRAUN
LONG TERM...ALLEN
AVIATION...AEM
FIRE WEATHER...BRAUN








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