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000
FXUS65 KRIW 021804
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1104 AM MST MON DEC 2 2013

.PREV DISCUSSION... /ISSUED 1027 AM MST MON DEC 2 2013/

.SHORT TERM...MONDAY THROUGH WEDNESDAY NIGHT
UPDATED TO ADD WINTER WEATHER HIGHLIGHTS ACROSS AREAS EAST OF THE
DIVIDE AND DOWN IN THE SOUTH AND SOUTHWEST FROM TONIGHT THROUGH
WEDNESDAY. ISSUED A WINTER STORM WATCH ALSO FOR OUR SERN ZONES DUE
TO THE POTENTIAL OF A LONG DURATION 1-2 PUNCH STORM...BITTER COLD
TEMPS AND STRONG NORTH TO NORTHEAST WIND. WILL UPGRADE TO A WINTER
WEATHER ADVISORY OR WINTER STORM WARNING BY LATER THIS AFTERNOON.
AMOUNTS ARE STILL THE MAIN QUESTION. WILL CONTINUE TO MONITOR.
MAINLY GOING 2 TO 4 INCHES EXCEPT 4 TO 8 IN THE WATCH AREA LOWER
ELEVATIONS WITH A FOOT OR SO POSSIBLE ON CASPER MOUNTAIN.

THE COMPLEX WEATHER SITUATION CONTINUES TO THROW MORE CURVE BALLS AT
THE WEATHER OFFICE TODAY THAN SANDY KOUFAX...OR BURT BLYLEVEN OR
CLAYTON KERSHAW DEPENDING ON YOUR ERA. ANYWAY...WE WILL DO THE SAME
AS YESTERDAY AND SPLIT THE DISCUSSION INTO WEST OF THE DIVIDE AND
EAST OF THE DIVIDE.

WEST OF THE DIVIDE...THE STORM BEGAN YESTERDAY AND CONTINUES TO BE
ONGOING AT THIS TIME. HAVE TO EAT A LITTLE CROW THIS MORNING AS I
IGNORED THE NAM 700 MILLIBAR TEMPERATURES THAT SHOWED SOME WARMER
AIR ADVECTING INTO THE WEST. THE FOREMENTIONED 700 MILLIBAR
TEMPERATURES HAVE RISEN TO AROUND -3 TO -4...WHICH PUTS SNOW LEVELS
AROUND 6500 TO 7000 FEET. AND...PLACES IN THE JACKSON AND STAR
VALLEYS HAVE SEEN A MIX AND IN SOME CASES A CHANGEOVER TO RAIN. THE
NAM DOES SHOW COLDER AIR WORKING BACK IN THIS MORNING SO
PRECIPITATION SHOULD CHANGE BACK OVER TO SNOW BY AROUND 9 AM.
HOWEVER...THIS WILL HOLD ACCUMULATIONS DOWN A BIT SO WE LOWERED THEM
SOMEWHAT...ALTHOUGH STILL IN WARNING CRITERIA. MEANWHILE...THE
HIGHER ELEVATIONS HAVE SEEN SOME IMPRESSIVE TOTALS WITH SOME SNOTELS
IN YELLOWSTONE AND THE TETONS SEEING CLOSE TO A FOOT OF SNOW
ALREADY. THE PRECIPITATION HAS BEEN BANDED THOUGH SO THERE ARE SOME
DIFFERENCES AND PINPOINTING THAT IS NEARLY IMPOSSIBLE. SO...THE
AMOUNTS IN THE MOUNTAINS STILL LOOK GOOD. NOT TOO MUCH CHANGE IN THE
REASONING OF THE FORECAST WITH ON AND OFF SNOW TODAY AND THEN A
LIKELY BURST OF HEAVY SNOW AS THE ARCTIC FRONT DROPS SOUTHWARD
ACROSS THE AREA LATE THIS AFTERNOON INTO TONIGHT WITH THE COLDEST
AIR SO FAR THIS SEASON. THIS FRONT SHOULD ALSO SHUT OFF A LOT OF THE
MOISTURE SO THE SNOW WILL BECOME LIGHT AS WELL AS THE WIND. AS FOR
THE REMAINDER OF THE PERIOD...VERY COLD WEATHER WILL BE THE RULE
WITH 700 MILLIBAR TEMPERATURES AS LOW AS 25 BELOW ACROSS PORTIONS OF
THE AREA. THIS MEANS HIGHS IN THE SINGLE DIGITS AT BEST AND LOWS
WELL BELOW ZERO. AS FOR SNOW...WE CONTINUED TO DROP POPS AND QPF.
THERE WILL BE A FEW SNOW SHOWERS AROUND BUT ANY ACCUMULATION SHOULD
BE LIGHT.

EAST OF THE DIVIDE...THERE ARE TRIPLE CONCERNS HERE WITH THE FIRST
BEING WIND...THE SECOND SNOW AND THIRD THE BITTER COLD. WE WILL
START WITH THE WIND. AT THIS TIME WE HAVE MULTIPLE HIGH WIND
WARNINGS IN EFFECT ACROSS THE AREA. THE ONE FROM EASTERN SWEETWATER
COUNTY INTO NATRONA STILL LOOKS REASONABLE. SOME OF THE WINDIER
SPOTS LIKE CAMP CREEK AND FALES ROCK HAVE ALREADY GUSTED PAST 50 MPH
AND WITH THE PRESSURE GRADIENT TIGHTENING WINDS SHOULD INCREASE. THE
ONE FOR NATRONA COUNTY LOWER ELEVATIONS IS A BIT MORE QUESTIONABLE
BUT WITH 700 MILLIBAR WINDS EXPECTED TO BE 50 TO 60 KNOTS AND GOOD
MIXING EXPECTED WE WILL KEEP IT GOING. I HAVE MORE QUESTIONS ABOUT
THE ONE IN THE CODY FOOTHILLS THROUGH. CONDITIONS ARE NOT IDEAL
THERE. FOR NOW...WE WILL KEEP IT GOING ALTHOUGH I COULD SEE IT BEING
CANCELLED EARLY. NOW...AS FOR THE LANDER FOOTHILLS...THERE IS ENOUGH
OF A PRESSURE GRADIENT WITH 10 MILLIBARS ACROSS THE STATE. THE WIND
DOES ALSO GO WEST BUT NOT UNTIL THE AFTERNOON. AS A RESULT WE WILL
UPGRADE IT TO A HIGH WIND WARNING BUT NOT START IT UNTIL 11 AM.
OTHER AREAS SHOULD REMAIN SUB WARNING BUT IT WILL BE WINDY THIS
AFTERNOON SO A HAT ALERT IS IN EFFECT.

NOW FOR THE SNOW POTENTIAL. NO CONCERNS DURING THE DAY TODAY AS
TEMPERATURES WILL BE MILD. A FEW SPOTS COULD EVEN GET CLOSE TO 60 IF
WINDS KICK IN THIS AFTERNOON...SUCH AS LANDER. THE EXCEPTION LOOKS
TO BE THE BIGHORN RANGE ALTHOUGH AMOUNTS SHOULD BE LIGHT DURING THE
DAY. THE ARCTIC FRONT WILL DROP INTO NORTHERN WYOMING THIS EVENING
AND THEN PLUNGE SOUTHWARD ACROSS THE AREA THROUGH THE NIGHT. IT
COULD BE ACCOMPANIED BY A BRIEF...HEAVY BAND OF SNOW WITH ITS
PASSAGE. HOWEVER...AMOUNTS IN MOST AREAS SHOULD BE LIGHT. BOTH THE
NAM AND GFS DO SHOW AN AREA OF ENHANCEMENT ACROSS EASTERN PORTIONS
OF THE AREA INCLUDING BUFFALO AND CASPER SO THIS WILL HAVE TO BE
WATCHED. THE MODELS THEN SPLIT AS TO SNOW POTENTIAL FOR TUESDAY AND
WEDNESDAY WITH POTENTIAL OVERRUNNING. THE EUROPEAN IS THE MOST
BULLISH MODEL IN KEEPING DECENT OVERRUNNING OVER MUCH OF THE AREA
WHICH WOULD LEAD TO LIGHT SNOW OVER MUCH OF THE SOUTHERN TWO THIRDS
OF THE AREA THROUGH WEDNESDAY WITH A TROUGH AXIS LINGERING TO THE
WEST. THE NAM...IN CONTRAST...DRIES THINGS OUT QUITE A BIT WITH ONLY
VERY LIGHT SNOW. THE GFS PLAYS THE MIDDLE GROUND BUT STILL KEEPS
STEADY SNOW CONFINED TO SOUTHERN WYOMING. FOR NOW...WE TOOK POPS
DOWN A BIT BUT STILL LEFT THEM AS LIKELY GIVEN THE UNCERTAINTY. AS
FOR ADVISORIES...SOME MAY BE NEEDED BUT SINCE SNOW IS NOT EXPECTED
TO START IN MOST AREAS UNTIL THIS EVENING WE WILL LET THE DAY
SHIFT MAKE THAT DECISION.

NOW FOR POSSIBLY THE BIGGEST EFFECT...THE COMING OF THE BITTERLY
COLD TEMPERATURES FOR MUCH OF THE AREA. AFTER A MILD DAY TODAY...THE
TEMPERATURES WILL NOT BE A SLAP IN THE FACE...MORE LIKE AN UPPERCUT
TO THE JAW FROM MIKE TYSON. TEMPERATURES WILL PLUMMET AFTER THE
FRONTAL PASSAGE TONIGHT. AND...WITH STRONG COLD ADVECTION CONTINUING
INTO TUESDAY...TEMPERATURES WILL CONTINUE TO FALL DURING THE DAY ON
TUESDAY. BY LATE TUESDAY NIGHT...SOME PORTIONS OF THE COUNTY WARNING
COULD BE AS MUCH AS 60 DEGREES COLDER THAN THE HIGH TEMPERATURES
TODAY...ALL THIS IN AROUND 36 HOURS. BY EARLY WEDNESDAY MORNING 700
MILLIBAR TEMPERATURES OF MINUS 20 WILL SPREAD ACROSS THE ENTIRE AREA
AND AS A RESULT LOW TEMPERATURES BELOW ZERO ARE EXPECTED TO BE
WIDESPREAD BY WEDNESDAY MORNING. TEMPERATURES ON WEDNESDAY AFTERNOON
WILL LIKELY NOT RISE TO ZERO IN A LOT OF AREAS. EVEN COLDER
TEMPERATURES ARE EXPECTED FOR WEDNESDAY NIGHT WITH TEENS BELOW ZERO
IN MANY LOCATIONS. STILL A BIT OF UNCERTAINTY AS TO HOW COLD THINGS
WILL GET...SINCE A LOT DEPENDS ON SNOW COVER. 4 TO 6 INCHES OF SNOW
COULD BRING BRUTAL COLD WITH A STRONG ALBEDO AND GOOD RADIATIONAL
COOLING. ONLY AN INCH OR TWO OF SNOW FALLS...NOT QUITE AS MUCH BIT
STILL PRETTY DARN COLD. IF THE BREEZE KEEPS UP...WE COULD BE LOOKING
AT POSSIBLE WIND CHILL WARNINGS FOR THE MIDDLE OF THE WEEK. WITH
THIS UNCERTAINTY...WE MADE FEW CHANGES TO CONTINUITY.
REGARDLESS...IT LOOKS LIKE ONE OF THE COLDEST STRETCHES OF WEATHER
IN QUITE A WHILE.

.LONG TERM...THURSDAY THROUGH MONDAY

THE EXTENDED WILL BE EXTREMELY COLD WITH TEMPERATURES SOME 20 TO 30
DEGREES BELOW AVERAGE. SINGLE DIGIT HIGHS WILL BE COMMON ACROSS THE
LOWER ELEVATIONS THURSDAY AND FRIDAY...WITH SOME AREAS POSSIBLY
NEVER GETTING ABOVE ZERO.

SOME VERY LIGHT SNOW/FLURRIES WILL BE POSSIBLE THURSDAY...MAINLY
OVER THE MOUNTAINS. MEDIUM RANGE MODELS SHOW A SHORTWAVE TROUGH
DIGGING SOUTH SOUTHEAST...INTO THE PACIFIC NORTHWEST/NORTHERN GREAT
BASIN LATE THURSDAY NIGHT/FRIDAY. THIS TROUGH IS THEN EXPECTED TO
GRADUALLY SHIFT ACROSS THE ROCKIES SATURDAY AND SUNDAY...WITH THE
GFS FASTER THAN THE ECMWF.  BOTH THE GFS/ECMWF MODELS ARE SHOWING A
GOOD SHOT AT LIGHT SNOW ACROSS THE WEST FRIDAY AND SATURDAY...WITH
SNOWFALL EAST OF THE DIVIDE MORE SPOTTY. THE ECMWF LINGERS THE
SNOWFALL INTO SUNDAY...WHILE THE GFS HAS MAINLY DRY CONDITIONS.

&&

.AVIATION.../18Z ISSUANCE/

STILL ANTICIPATING CHANGE TO MUCH COLDER WEATHER BEGINNING TONIGHT.
LIGHT TO MODERATE SNOW TO CONTINUE IN THE MOUNTAINS AND FAR WESTERN
VALLEYS TODAY. MVFR CONDITIONS ARE LIKELY IN THOSE AREAS...FOLLOWED BY
MVFR TO IFR CONDITIONS MOST AIRPORT LOCATIONS LATER TONIGHT AND TUESDAY.
ARCTIC COLD FRONT TO IMPACT MUCH OF FORECAST AREA BETWEEN 09Z-12Z
TUESDAY MORNING. GUSTY WEST TO SOUTHWEST SURFACE WINDS WILL
PRECEDE THIS FRONT. STILL POSSIBLE THAT WIND WILL GUST TO AROUND
50 MPH ON LEE SIDE OF MOUNTAIN RANGES THIS AFTERNOON AND EARLY EVENING.

&&

.FIRE WEATHER...

HEAVY SNOW IS EXPECTED IN WESTERN WYOMING THROUGH MONDAY NIGHT IN
WESTERN WYOMING. VERY STRONG WINDS ARE EXPECTED IN AREAS EAST OF THE
DIVIDE AS WELL AS IN SWEETWATER COUNTY TODAY. ARCTIC AIR WILL PLUNGE
SOUTH MONDAY NIGHT AND TUESDAY. BITTER COLD WEATHER AND LIGHT SNOW
IS EXPECTED FOR THE REMAINDER OF THE WEEK.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WARNING UNTIL 5 PM MST THIS AFTERNOON WYZ019-020-030.

WINTER STORM WATCH FROM THIS EVENING THROUGH WEDNESDAY AFTERNOON
WYZ019-020-022-030.

HIGH WIND WARNING UNTIL 6 PM MST THIS EVENING WYZ018.

WINTER WEATHER ADVISORY FROM 11 PM THIS EVENING TO 5 PM MST
WEDNESDAY WYZ015-017-018.

WINTER STORM WARNING UNTIL 5 AM MST TUESDAY
WYZ001-002-012>014-023>025.

WINTER WEATHER ADVISORY FROM 5 PM THIS AFTERNOON TO 5 PM MST
WEDNESDAY WYZ008>011-027.

HIGH WIND WARNING UNTIL 11 AM MST THIS MORNING WYZ003.

WINTER WEATHER ADVISORY FROM 5 PM THIS AFTERNOON TO 5 PM MST
TUESDAY WYZ003-004.

WINTER WEATHER ADVISORY FROM 8 PM THIS EVENING TO 5 PM MST
WEDNESDAY WYZ028-029.

WINTER WEATHER ADVISORY FROM 8 PM THIS EVENING TO 5 PM MST
TUESDAY WYZ005>007.

&&

$$

SHORT TERM...SKRBAC
LONG TERM...WM
AVIATION...KPL
FIRE WEATHER...HATTINGS