Weather Service Report


428 
FXUS65 KRIW 241251
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
551 AM MST MON NOV 24 2014

.UPDATE...
CONTINUES TO LOOK VERY INTERESTING FOR THE NW MOUNTAINS AND
SURROUNDING AREA FOR HEAVY SNOW BEGINNING LATER TONIGHT THROUGH
TUESDAY NIGHT. STRONG ISENTROPIC UPGLIDE PATTERN IS PRODUCING SOME
PRETTY IMPRESSIVE TIME HEIGHTS IN THE NW. DENDRITIC GROWTH ZONE
TEMPERATURES DO GET A LITTLE WARM WITH TIME BUT IT'S HARD TO
IGNORE THE 30-50KT MTN TOP FLOW AND STEADY PCPN FOR 24 HOURS OR
MORE. WILL KEY IN ON THE FAVORED WNW FLOW AREAS WITH OTHER AREAS
LIKELY NEEDING ADVISORIES WITH THE AFTERNOON PACKAGE. THERE WILL
BE POTENTIAL FOR A CHANGEOVER TO RAIN OR RAIN AND SNOW BY LATE
TUESDAY OR TUESDAY NIGHT...ESPECIALLY IN THE STAR VALLEY. UPDATE
GOING OUT ASAP.

&&

.SHORT TERM...TODAY THROUGH WEDNESDAY NIGHT

WITH THE DIFFERENCES IN THE WEATHER ACROSS THE AREA...ONE AGAIN WE 
WILL SPLIT THINGS UP WITH THE CONTINENTAL DIVIDE AS THE SPLIT.

WEST OF THE DIVIDE...YET ANOTHER IN THE SERIES OF SHORTWAVES 
CONTINUES TO MOVE THROUGH THE STATE. A DECENT BAND OF SNOW HAS 
DEVELOPED IN IDAHO AND IS NOW DROPPING SOUTHWARD ACROSS THE WEST. IT 
COULD BRING A QUICK INCH OR TWO TO SOME LOCATIONS. THE GOOD NEWS IS 
THAT IT IS MOVING SOUTH AT A DECENT CLIP AT THIS TIME SO IT SHOULD 
MOVE THROUGH FAIRLY QUICKLY. THE SNOW SHOULD TAPER OFF FAIRLY 
QUICKLY TOWARD MORNING THOUGH. TODAY WILL BE A PERIOD IN BETWEEN 
SYSTEMS SO HEAVY SNOW IS NOT EXPECTED. HOWEVER...WITH NORTHWEST FLOW 
CONTINUING THERE WILL BE ISOLATED TO SCATTERED SNOW SHOWERS THROUGH 
THE DAY. THE NEXT SYSTEM...THIS ONE WITH A LITTLE MORE PUNCH WILL 
MOVE TOWARD THE AREA TONIGHT. THE MODELS STILL HAVE SOME DIFFERENCES 
IN TIMING WITH THE NAM A BIT SLOWER THAN THE OTHER MODELS. FOR 
NOW...WE STARTED WITH LOW POPS AND RAMPED THEM UP THROUGH THE NIGHT 
AND INTO TUESDAY. THIS SYSTEM DOES HAVE SOME DECENT LIFT WITH SOME 
WARM ADVECTION AS WELL. SOME HIGHLIGHTS ARE ANTICIPATED WITH THIS 
SYSTEM. HOWEVER...THE MODELS HAVE BEEN OVERDOING THE QPF WITH THESE 
SHORTWAVES THE PAST WEEK OR SO. SO ALTHOUGH WE DID INCREASE SNOWFALL 
AMOUNTS...WE KEPT THEM BELOW WARNING CRITERIA. SOME ADVISORIES WILL 
PROBABLY BE NEEDED TO BE ISSUED LATER TODAY HOWEVER. THIS SNOW WILL 
CONTINUE THROUGH TUESDAY NIGHT AS WELL. CONDITIONS SHOULD BEGIN TO 
IMPROVE WEDNESDAY MORNING AS THE SYSTEM MOVES AWAY AND RIDGING 
BEGINS TO BUILD ACROSS WYOMING. THE MODELS HAVE BEGUN TO COME INTO 
BETTER AGREEMENT WITH RIDGING CONTINUING TO BUILD ACROSS THE STATE 
LATER WEDNESDAY AND INTO WEDNESDAY NIGHT. AS A RESULT...WE HAVE 
TRIMMED POPS FOR LATER WEDNESDAY AND WEDNESDAY NIGHT. WITH THE 
RECENT DIFFERENCES IN THE MODELS...WE DID NOT REMOVE THEM YET AND 
WOULD PREFER TO WAIT ANOTHER RUN OR TWO TO DRY THINGS OUT 
COMPLETELY. 

EAST OF THE DIVIDE...THE RADAR IS SHOWING SOME ECHOES ACROSS THE 
AREA. HOWEVER...ALL OF THIS ACTIVITY HAS NOT REACHED THE GROUND YET 
WITH THE DRY ATMOSPHERE IN PLACE. WITH THE SHORTWAVE MOVING THROUGH 
THE AREA...EXPECT ANOTHER BREEZY TO WINDY DAY FOR MANY AREAS. OF 
PARTICULAR CONCERN ARE AREAS ACROSS SWEETWATER COUNTY WHERE 700 
MILLIBAR WINDS ARE APPROACHING 50 TO 55 KNOTS LATE TONIGHT. 
HOWEVER...AT THIS TIME WE DO NOT THINK WINDS THIS STRONG WILL MIX TO 
THE SURFACE. THERE COULD BE SOME GUSTS TO 50 MPH HOWEVER. WINDS 
SHOULD GRADUALLY DECREASE THROUGH THE AFTERNOON AS WINDS ALOFT RELAX 
A BIT. AS FOR THE CHANCE OF PRECIPITATION...BOTH THE NAM AND GFS 
SHOW SOME LIGHT PRECIPITATION OCCURRING FROM THE EASTERN BIG HORN 
BASIN DOWN THROUGH EASTERN FREMONT AND EASTERN SWEETWATER COUNTIES 
AND EASTWARD. FURTHER WEST...WITH DOWNSLOPING FLOW MOST AREAS SHOULD 
STAY DRY. PRECIPITATION AMOUNTS STILL LOOK FAIRLY LIGHT THOUGH. THE 
MOUNTAINS COULD SEE A COUPLE OF INCHES HOWEVER. 

FOR TONIGHT...ATTENTION TURNS TOWARD THE CHANCE OF HIGH WINDS ACROSS 
FAVORED AREAS IN THE ABSAROKAS AND CODY FOOTHILLS...INCLUDING THE 
CROSSROADS OF AMERICA...CLARK. 700 MILLIBAR WINDS ARE EXPECTED TO 
INCREASE TO 60 TO 65 KNOTS BY EARLY TUESDAY MORNING. IN 
ADDITION...BY EARLY TUESDAY MORNING THE AREA WILL BE IN THE FAVORED 
RIGHT FRONT QUAD OF THE JET TO PROVIDE SOME DOWNWARD FORCING. SO AS 
A RESULT WE WILL CONTINUE THE HIGH WIND WATCH. THE NEXT QUESTION IS 
HOW MUCH PRECIPITATION WILL MAKE IT OVER THE DIVIDE FOR TUESDAY AND 
TUESDAY NIGHT.  THE MODELS ARE IN FAR AGREEMENT IN THE AREA BEING 
MAINLY ACROSS PORTIONS OF THE BIG HORN BASIN...ESPECIALLY IN THE 
EAST AND TO THE EAST AS WELL AS NORTH OF THE OWL CREEK RANGE. WITH 
THE FAVORED NORTHWEST FLOW...THE BIGHORN MOUNTAINS COULD DO 
PARTICULARLY WELL WITH THIS SETUP. HOWEVER...EVEN THE LOWER 
ELEVATIONS COULD SEE A FEW INCHES OF SNOW. THERE IS STILL SOME 
DISAGREEMENT IN THE DETAILS HOWEVER. THE NEXT CONCERN IS FOR WIND. 
THE MODELS CONTINUE TO SHOW SOME VERY STRONG WINDS ALOFT WITH 50 TO 
60 KNOTS AT 700 MILLIBARS ACROSS MUCH OF THE AREA. HOWEVER...ONE 
NEGATIVE IS THAT CLOUD COVER MAY HELP TO LIMIT MIXING...ESPECIALLY 
WITH THE STRONGEST WINDS EXPECTED AT NIGHT. THE EXCEPTION ONCE AGAIN 
MAY BE AREAS NEAR CLARK...BUT WE WILL CROSS THAT BRIDGE TOMORROW. 
CONDITIONS SHOULD ONCE AGAIN IMPROVE ON WEDNESDAY AS THE SYSTEM 
LIFTS OUT. AND...LIKE WHAT WAS STATED IN WEST OF THE DIVIDE...THE 
MODELS HAVE TRENDED TOWARD RIDGING FOR WEDNESDAY AND WEDNESDAY NIGHT 
AND MAINLY DRY BUT WINDY CONDITIONS FOR WEDNESDAY NIGHT.

.LONG TERM...THURSDAY THROUGH MONDAY

GFS SEEMS TO BE ON A WINNING STREAK THE PAST FEW SYSTEMS WITH BOTH 
THE ECMWF...GEM AND ECMWF ENSEMBLES NOW FOLLOWING THE GFS LEAD WITH 
OUR THANKSGIVING WEEKEND WEATHER SYSTEMS. A DRAMATIC TURN FROM LAST 
NIGHT WHEN THE GFS WAS AN OUTLIER. END RESULT IS A MUCH MILDER 
THURSDAY/FRIDAY BEFORE WE FINALLY GET A COLD FRONT FROM THE NORTH 
FRIDAY NIGHT INTO SATURDAY. SHOULD GET SOME DECENT SNOW ACROSS THE 
WEST IN THE MOIST...SAGGING WLY FLOW FRIDAY INTO SATURDAY. HOW MUCH 
IF ANY WE GET EAST OF THE DIVIDE IS STILL UNCERTAIN...ESPECIALLY 
AFTER THE WAY THE MODELS HAVE STRUGGLED THE PAST FEW DAYS. 
ALTHOUGH...THEY HAVE GENERALLY BEEN PICKING UP ON THIS FRIDAY NIGHT/
SATURDAY SYSTEM FOR A WHILE IT WAS JUST THE INITIAL SHORTWAVE ON 
THANKSGIVING THAT THEY'VE BEEN STRUGGLING WITH. IT NOW APPEARS THIS 
WAVE WILL WEAKEN IN THE CONFLUENT FLOW AND INFLUENCE OF WARM AIR 
BEING PUMPED UP AHEAD OF THE NEW ERN PACIFIC UPPER LOW. SO BOTTOM 
LINE...IT LOOKS LIKE A NICE THANKSGIVING DAY NOW WITH SNOW MOVING 
INTO THE WRN MOUNTAINS MAINLY LATER FRIDAY OR FRIDAY EVENING... 
CONTINUING THROUGH SATURDAY. VALLEYS COULD BE RAIN OR RAIN AND SNOW 
MIX INITIALLY...ESPECIALLY THE STAR VALLEY WITH H7 TEMPERATURES
STARTING AS WARM AS -1C AT H7 ONLY NOT COOLING SIGNIFICANTLY UNTIL
FRIDAY NIGHT AND SATURDAY. WINDS WILL ALSO BE ON THE INCREASE
THANKSGIVING DAY INTO FRIDAY WITH POTENTIAL FOR SOME HIGH WINDS BY
FRIDAY IN THE WIND CORRIDOR AND CODY FOOTHILLS. MAYBE AS EARLY AS
THURSDAY NIGHT IN THE CODY FOOTHILLS. COLDER EAST OF THE DIVIDE
SATURDAY WITH SHORTWAVE PASSING OFF TO THE EAST BUT PUSHING A
DECENT SURFACE HIGH AND ASSOCIATED COLD FRONT SWD INTO AREAS EAST
OF THE DIVIDE. ON SUNDAY...HEIGHTS START TO BUILD AS STRONG
PACIFIC SYSTEM STARTS TO MOVE ONTO THE WEST COAST WITH WARMING MID
LEVEL TEMPERATURES AND POTENTIAL FOR LIGHT MOUNTAIN SNOW OUT WEST.
SNOW WILL LIKELY BE ON THE INCREASE MONDAY AS TROUGH MOVES INTO
THE GREAT BASIN AND INTER-MOUNTAIN WEST. EAST OF THE
DIVIDE...WE'LL HAVE TO WATCH THIS EVOLUTION CLOSELY COLD AIR WILL
BE LURKING JUST TO THE NORTH AND SURFACE LOW MAY DEVELOP OVER SRN
WYO OR NRN CO AT THE END OF THIS PERIOD.

&&

.AVIATION.../12Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES 
A FAST-MOVING UPPER LEVEL DISTURBANCE WILL CONTINUE TO PUSH SE 
ACROSS WYOMING EARLY THIS MORNING SPREADING AREAS OF LIGHT SNOW AND 
FRQT MTN OBSCURATIONS ACROSS THE BIGHORN RANGE WITH LOCAL AREAS OF 
MVFR -SN MAINLY VCNTY AND EAST OF A KCOD-KWRL-KCPR LINE THROUGH 
15Z.  DRIER AIR WILL PUSH NW-SE BEHIND THIS SYSTEM 15Z-18Z MONDAY.  
GUSTY NW SFC WINDS WILL CONTINUE THROUGH MID-AFTN...ESPECIALLY VCNTY 
KDUB-KRIW AND EAST OF THE BIGHORN RANGE.  THERE WILL BE SOME 
DECREASE IN THE WIND 21Z MON-03Z TUE AND THEN RIDGE TOP WEST WINDS 
WILL INCREASE TO 40-50KTS ALONG THE EAST SLOPES OF THE DIVIDE WITH 
MOUNTAIN WAVE ACTIVITY LIKELY ALONG WITH AREAS OF LLWS VCNTY 
KCOD-KDUB 3Z-12Z TUESDAY.  

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES
A FAST-MOVING UPPER LEVEL DISTURBANCE WILL CONTINUE TO DIVE SE ALONG 
THE DIVIDE EARLY THIS MORNING WITH AREAS OF MVFR/IFR -SN AND 
WIDESPREAD MTN OBSCURATIONS SHIFTING INTO SW WY THROUGH 15Z.  DRIER 
AIR WILL PUSH INTO THE NW BEHIND THE SYSTEM EARLY THIS MORNING WITH 
OVERALL IMPROVING CONDITIONS...THOUGH GUSTY WINDS WILL CONTINUE TO 
CAUSE OCNL MVFR VSBY VCNTY KJAC.  MOST OF THE MVFR/IFR -SN WILL EXIT 
SW WY BY 15Z.  GUSTY NW SFC WINDS WILL FOLLOW THE SYSTEM THROUGH 
MONDAY AFTN...ESPECIALLY ACROSS THE UPPER GREEN RIVER BASIN AND 
INTERSTATE 80 CORRIDOR.  A MOIST WESTERLY FLOW WILL BRING INCREASING 
SNOWFALL VCNTY AND NORTH OF A KPNA-KEMM LINE 08Z-12Z TUESDAY WITH 
WIDESPREAD MVFR -SN...AREAS OF IFR -SN EXPECTED BY 12Z ALONG WITH 
MTNS MOSTLY OBSCD.

&&

.FIRE WEATHER...

NORTHWEST FLOW ALOFT WILL REMAIN OVER WESTERN AND CENTRAL WYOMING.
A FAST MOVING PACIFIC LOW PRESSURE TROUGH IN THE FLOW WILL SWEEP
THROUGH THE AREA THIS MORNING. THE NORTHERN AND WESTERN MOUNTAINS
WILL SEE SOME LIGHT SNOWFALL. SOME OF THE SNOW WILL MAKE IT TO THE
VALLEYS OF THE WEST. EAST OF THE DIVIDE LITTLE IF ANY SNOWFALL IS
EXPECTED BUT BRISK NORTHWEST WINDS WILL CONTINUE. THE SNOWFALL IN
THE WEST AND NORTH SHOULD TAPER OFF FROM LATE MORNING THROUGH
EARLY AFTERNOON. RELATIVE HUMIDITY WILL BE ELEVATED WITH GENERALLY
LOW MIXING HEIGHTS. WINDIER AREAS MAY SEE FAIR SMOKE DISPERSAL IN
THE AFTERNOON EAST OF THE CONTINENTAL DIVIDE. ANOTHER MORE POTENT
SYSTEM WILL BRING MORE SNOW TO THE WEST STARTING LATER MONDAY NIGHT.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WATCH FROM THIS EVENING THROUGH TUESDAY MORNING 
WYZ002-003.

WINTER STORM WATCH FROM LATE TONIGHT THROUGH LATE TUESDAY NIGHT 
WYZ012-013.

&&

$$

SHORT TERM...HATTINGS
LONG TERM...SKRBAC
AVIATION...AEM
FIRE WEATHER...HATTINGS




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