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000
FXUS65 KRIW 022158
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
258 PM MST MON DEC 2 2013

.SHORT TERM...TONIGHT THROUGH THURSDAY
SNOW...HEAVY AT TIMES...WILL CONTINUE OUT WEST THROUGH THE EVENING
AS A STRONG PACIFIC COLD FRONT MOVES INTO THE AREA. INTENSE SNOWFALL
WILL LIKELY OCCUR THROUGH THE EVENING ALONG WITH THE STRONGEST WINDS
OF THE STORM ALONG WITH FALLING TEMPERATURES. THE ARCTIC COLD FRONT
CURRENTLY PUSHING INTO SRN MONTANA WILL PUSH SOUTH ACROSS CENTRAL
AND NORTHWEST WYOMING TONIGHT AND INTO FAR SRN AND SWRN WYOMING ON
TUESDAY. THIS ARCTIC AIRMASS WILL BE THE TRANSITION FROM SIGNIFICANT
SNOW IN THE WEST TO SIGNIFICANT COLD AND SNOW EAST OF THE DIVIDE.
THIS ARCTIC FRONT SHOULD HAVE A GOOD PUNCH TO IT WITH 25 TO 35 DEW
POINTS AHEAD OF IT AND EXPECTED DECENT FRONTAL FORCING. 3HR PRESSURE
RISES AROUND 6MB SHOULD PRODUCE A PERIOD OF VERY STRONG WINDS IN THE
NORTH HALF...SPREADING SOUTH ON TUESDAY.

THE PACIFIC PORTION OF THE FRONT WILL ALSO PROVIDE A PERIOD OF
ENHANCED SNOWFALL IN OUR SRN ZONES TONIGHT ALONG WITH STRONG WEST
WINDS. THESE WINDS WILL TURN ELY TUESDAY AFTERNOON AND EVENING AND
BECOME QUITE STRONG AGAIN. THE COMBINATION OF THE BITTER COLD
AIRMASS...UPSLOPE...WIND CHILLS AND ACCUMULATING SNOWFALL WARRANTS
HIGHLIGHTS IN MANY AREAS. MOST WILL BE UNDER A WINTER WEATHER
ADVISORY EAST OF THE DIVIDE AND IN THE FAR SOUTH THROUGH WEDNESDAY.
THE AREA FROM NEAR ROCK SPRINGS TO CASPER HAS THE BEST CHANCE OF
MORE SIGNIFICANT SNOW COMBINED WITH WIND CHILLS OF -30 TO 35 BELOW
ZERO AND STRONG NORTH TO NORTHEAST WINDS TUESDAY INTO WEDNESDAY. THE
MAIN MODEL TRENDS AGAIN TODAY IS TO PUT MORE EMPHASIS ON THE UPPER
LOW MOVING SWWD FROM MT INTO ID ON TUESDAY AND THEN TRACKING EWD
ACROSS US ON WEDNESDAY. THIS INCREASES THE CHANCES AGAIN OF BETTER
SNOWFALL IN THE EAST. THE COMBINATION OF THE UPSLOPE...ISENTROPIC
UPGLIDE...QG FORCING AND POSSIBLE LEFT EXIT REGION JET STREAK
DYNAMICS WARRANTS OUR ATTENTION. WE ISSUED WINTER STORM WATCHES
EARLIER FOR EASTERN SWEETWATER COUNTY OVER TO CASPER FOR LATER
TONIGHT THROUGH WEDNESDAY AS THIS AREA LOOKS TO HAVE THE BEST OF THE
FORCING AND LONGEST DURATION OF SNOW. WARNING AMOUNTS MAY BE
MARGINAL BUT WITH THE HIGH IMPACT POTENTIAL DUE TO BITTER WIND
CHILLS TO -35 AND POSSIBLE WHITEOUT CONDITIONS DUE TO THE FLUFFY
SNOW BLOWING AROUND EASY...WE ARE OPTING TO UPGRADE OUR WINTER STORM
WATCH TO A WINTER STORM WARNING. MOST OF THE REST OF THE AREA WILL
CONTINUE WITH WINTER WEATHER ADVISORIES.

IN GENERAL...2 TO 4 INCHES IN THE LOWER ELEVATIONS OF THE ADVISORY
AREAS WITH 6 TO 12 IN THE MOUNTAINS. THE WARNING AREAS WILL HAVE 4
TO 8 INCHES EXCEPT AROUND A FOOT ON CASPER MOUNTAIN. INCREASING THE
SLR TO 20-1 FOR TUESDAY THROUGH WEDNESDAY WITH GENERAL QPF AMOUNTS
BETWEEN .15 AND .40 EAST OF THE DIVIDE IN THE LOWER ELEVATIONS.
BITTER COLD AIRMASS BECOMES WELL ENTRENCHED TUESDAY INTO WEDNESDAY
WITH LITTLE CHANGE THROUGH THURSDAY. THE SNOW WILL END OR BE REDUCED
TO OCCASIONAL FLURRIES WEDNESDAY NIGHT AND THURSDAY BUT IT WILL
REMAIN BITTER COLD. ANY AREA THAT HAS A MOSTLY CLEAR NIGHT COULD BE
EXTREMELY COLD THURSDAY MORNING. MANY AREAS WILL BE -10 TO -20 WITH
-30 IN YNP. DEPENDING ON THE TOTAL SNOW COVER SOME AREAS COULD BE
COLDER YET...ESPECIALLY IF THERE IS MORE THAN 4 OR 5 INCHES OF SNOW
ON THE GROUND IN THE EAST.

.LONG TERM...THURSDAY NIGHT THROUGH MONDAY
LOTS OF WINTER WEATHER TO OCCUR IN THE SHORT TERM ACROSS WEST
CENTRAL WYOMING...SO WILL KEEP THIS EXTENDED PORTION BRIEF TO LEAVE
FOCUS ON THE MORE ACTIVE WEATHER PATTERN.

THE DEPARTURE OF THIS SIGNIFICANT WINTER WEATHER SYSTEM WILL LEAVE A
VERY COLD AIRMASS TO CONTINUE TO COVER THE REGION THROUGH THE
EXTENDED PERIOD. MUCH BELOW NORMAL TEMPERATURES EXPECTED THROUGH
EARLY NEXT WEEK...WITH SINGLE DIGIT DAYTIME TEMPERATURES COMMON
THROUGH FRIDAY. TEMPERATURES MAY REBOUND SLIGHTLY DURING THE WEEKEND
ACROSS SOUTHERN WYOMING...THOUGH MODIFICATIONS TO THE AMOUNT OF
SNOWFALL ON THE GROUND WILL INFLUENCE THE DURATION OF COLDER
TEMPERATURES. MEDIUM RANGE MODELS DO DIFFER ON POSITION AND STRENGTH
OF SURFACE HIGH PRESSURE. CONFIDENCE NOT HIGH...BUT LIKELY TO KEEP
IN LOW LEVEL MOISTURE ESPECIALLY CENTRAL AND SOUTHERN PARTS OF
FORECAST AREA THROUGH THE WEEKEND. NORTHERN SECTIONS COULD HAVE MORE
SUNSHINE...BUT THE SUN WILL NOT HELP TEMPERATURES MUCH.

MODELS DO INDICATE THE POTENTIAL FOR ANOTHER WAVE OF LOW PRESSURE TO
APPROACH THE AREA AGAIN BY SUNDAY...THOUGH SPECIFIC LOCATION AND
INTENSITY OF ASSOCIATED PRECIPITATION DOES VARY WITH EACH MODEL.
THIS SYSTEM LOOKS TO PRIMARILY IMPACT THE WESTERN PORTION OF THE
FORECAST AREA WITH PRECIPITATION.

OVERALL...POPS WILL BE LOW ALTHOUGH FLURRIES OR VERY LIGHT SNOW
WILL LINGER IN THE HIGH COUNTRY WITH THE EXPECTED SYNOPTIC PATTERN.

.AVIATION.../00Z ISSUANCE/

NOT MUCH CHANGE FROM PREVIOUS AVIATION DISCUSSION. STILL
ANTICIPATING BIG CHANGE TO MUCH COLDER WEATHER BEGINNING TONIGHT.
LIGHT TO MODERATE SNOW TO CONTINUE IN THE MOUNTAINS AND FAR WESTERN
VALLEYS THIS EVENING. MVFR CONDITIONS ARE LIKELY IN THOSE
AREAS...FOLLOWED BY MVFR TO IFR CONDITIONS MOST AIRPORT LOCATIONS
ACROSS WEST CENTRAL WYOMING LATER TONIGHT AND TUESDAY. ARCTIC COLD
FRONT TO IMPACT NORTHERN SECTIONS OF WYOMING AROUND 06Z...THEN
PRETTY MUCH SWEEPS ACROSS THE REMAINDER OF STATE BETWEEN 09Z-12Z
TUESDAY MORNING. WIDESPREAD LIGHT SNOW JUST BEHIND THIS ARCTIC FRONT
AND CONTINUING THROUGH TUESDAY NIGHT. SNOW AND LOWER VISIBILITIES
WITH ASSOCIATED MVFR TO IFR CONDITIONS SHOULD THEN BE FOCUSED MORE
ALONG A KRKS TO KCPR LINE AFTER 18Z TUESDAY.

.FIRE WEATHER...

HEAVY SNOW IS EXPECTED IN WESTERN WYOMING THROUGH TONIGHT 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 TONIGHT AND TUESDAY AND REMAIN THROUGH THE REMAINDER
OF THE WEEK. SNOW WILL SHIFT EAST OF THE DIVIDE TONIGHT AND
CONTINUE THROUGH WEDNESDAY IN MANY AREAS UNDER A BITTER COLD AIRMASS.

&&

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

WINTER STORM WARNING FROM 11 PM THIS EVENING TO 5 PM MST
WEDNESDAY 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 UNTIL 5 PM MST WEDNESDAY WYZ008>011-027.

WINTER WEATHER ADVISORY UNTIL 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...KPL/BRANHAM
AVIATION...KPL/BRANHAM
FIRE WEATHER...SKRBAC