Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 252132
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
232 PM MST THU DEC 25 2014

.SHORT TERM...TONIGHT THROUGH FRIDAY
SNOWFALL IS GRADUALLY TAPERING OFF FROM NORTH TO SOUTH AFTER SOME
AREAS OF THE CWA LIKELY EXPERIENCED THE SNOWIEST CHRISTMAS ON
RECORD. ALPINE RECEIVED 12 INCHES OVERNIGHT. THE MAIN CIRCULATION
NOW APPEARS TO BE JUST SOUTH OF THE GREAT SALT LAKE. THE MID LEVEL
CIRCULATION WAS PROGGED TO TRACK SSE ACROSS SW WY TODAY. THE
COMBINATION OF THE CLOSE PROXIMITY OF THE MID LEVEL
CIRCULATION...QG FORCING DIRECTLY ASSOCIATED WITH THE MAIN
LOW...ISENTROPIC LIFT AROUND THE BACKSIDE OF THE LOW AS WELL AS
THE SURFACE CONVERGENCE WITH THE ASCT STRONG CANADIAN FRONT THAT
TRACKED SOUTH THIS MORNING ALL CONTRIBUTED TO THE SUBSTANTIAL
SNOWFALL ACROSS MUCH OF THE AREA...EAST AND WEST OF THE DIVIDE. IN
ADDITION...AREAS FROM THE LANDER FOOTHILLS AND THE NEARBY EAST
SLOPE OF THE WIND RIVERS TO THE GREEN MTNS TO CASPER HAVE BEEN
RECEIVING ADDITIONAL SNOWFALL FROM THE POST FRONTAL LOW LEVEL
UPSLOPE COMPONENT WITH LANDER RECEIVING AROUND HALF A FOOT OF SNOW
SO FAR. WITH THE MAIN LOW TRACKING FROM IDAHO LAST NIGHT TO UTAH TODAY
AND ON INTO THE FOUR CORNERS AREA FRIDAY HAS BEEN A FAVORABLE
TRACK FOR LND TO RECEIVE SIGNIFICANT SNOWFALL. AREAS IN THE
FAVORED UPSLOPE AREAS FROM LND TO CPR SHOULD SEE SEVERAL MORE
INCHES OF SNOWFALL THIS EVENING AS THE UPSLOPE DEEPENS ONCE THE
MID LEVEL CIRCULATION TRAVELS TO OUR SOUTH OVER THE UTAH/CO
BORDER...EVEN AS THE AFOREMENTIONED ENDING OF THE SNOW CONTINUES
THIS EVENING FROM NORTH TO SOUTH. THE SNOWFALL WILL CONTINUE TO
TAPER OFF OVER CENTRAL AND SOUTHERN WY AFTER MIDNIGHT TONIGHT WITH
DRY CONDITIONS ACROSS MOST OF THE NORTH. SOME LIGHT UPSLOPE
SNOWFALL WILL LIKELY LINGER THROUGH SUNRISE ABOVE CPR AND LANDER.
OTHERWISE...JUST SOME ISOLATED HIGH MTN FLURRIES WILL OCCUR FRIDAY
WITH MOSTLY CLOUDY SKIES SLATED FOR FRIDAY IN MOST AREAS AS THE
EAST SIDE OF THE MAIN TROUGH CONTINUES TO SLOWLY EXIT TO THE
SOUTHEAST. AS SKIES CLEAR AND WINDS CONTINUE TO TAPER OFF THROUGH
LATE TONIGHT AND WITH FRESH SNOW COVER ON THE GROUND...LOWS
TONIGHT WILL HAVE NO TROUBLE DROPPING TO THE SINGLE DIGITS MOST
AREAS AND BELOW ZERO IN THE NORTHWEST. FRIDAYS HIGH TEMPS WILL BE
A FEW DEGREES COLDER FRIDAY BEHIND THIS EXITING SNOWSTORM.

.LONG TERM...FRIDAY NIGHT THROUGH THURSDAY
WESTERN AND CENTRAL WYOMING WILL BE ON THE NORTHWEST FRINGE OF
THE LOW PRESSURE CIRCULATION WHICH WILL BE EXITING THE AREA.
MOUNTAIN AND EASTERN AREAS COULD SEE SOME VERY LIGHT SNOW.  COLD
NORTH FLOW WILL BE OVER THE AREA.  ADDED AREAS OF FOG IN THE VALLEYS
AND BASINS  WITH PARTIAL CLEARING OVER FRESH SNOW COVER.  SATURDAY
SHOULD BE DRY WITH LITTLE WARMING EXCEPT IN THE SOUTHWEST WHERE
WINDS WILL MIX THE LOWER AIR MASS.  BASIN COLD POOLS SHOULD RESIST
WARMING WITH WARM AIR ADVECTION IN THE MID LEVELS INCREASING SURFACE
BASED INVERSIONS.  AN APPROACHING PACIFIC LOW PRESSURE TROUGH WILL
BEGIN TO BRING SOME LIGHT SNOW TO THE NORTHWEST MOUNTAINS SATURDAY
AFTERNOON INCREASING THROUGH THE NIGHT.  INCREASED CLOUD COVER AND
WIND WILL ERODE AREAS OF COLD AIR ALONG THE EDGES OF THE BASINS.
THE WIND CORRIDOR ACROSS SWEETWATER...SOUTHERN FREMONT AND NATRONA
COUNTIES AND THE CODY FOOTHILLS WILL BECOME WINDY SATURDAY NIGHT AS
SNOW BECOMES MORE WIDESPREAD ACROSS THE WEST SPREADING INTO THE
SOUTHWEST.  SNOW WILL CONTINUE ACROSS THE WEST AND SOUTHWEST
DEVELOPING IN THE NORTH ON SUNDAY AS A COLD FRONT WORKS ITS WAY INTO
THE NORTH. SUNDAY NIGHT AND MONDAY ANOTHER LOW PRESSURE STORM SYSTEM
WILL WRAP UP AND DEEPEN OVER THE AREA WITH POTENTIAL WIDESPREAD
SNOWFALL ACROSS WESTERN AND CENTRAL WYOMING.  THIS WILL BE SUPPORTED
BY AN UPPER LEVEL LOW PRESSURE CENTER OVER NORTHEAST UTAH AND
NORTHWEST COLORADO PROVIDING UPPER AIR SUPPORT WITH UPPER LEVEL
DIVERGENCE AND MID LEVEL INSTABILITY OVER AN INTENSIFYING COLD
FRONT ALONG THE CONTINENTAL DIVIDE. MUCH OF THE AREA WILL SEE SNOW
THROUGH MONDAY AND MONDAY EVENING BEFORE THE LOW MOVES SOUTH AND
EAST THROUGH THE NIGHT WITH SNOWFALL ENDING FROM NORTHWEST TO
SOUTHEAST ACROSS THE AREA. CLEARING WILL OCCUR ON TUESDAY. A
CANADIAN COLD FRONT WILL BRING SOME ARCTIC AIR SOUTH LATE
WEDNESDAY AND WEDNESDAY NIGHT WITH A BETTER PUSH SOUTH ON
THURSDAY.

&&

.AVIATION.../00Z ISSUANCE/
AN UPPER LEVEL LOW PRESSURE SYSTEM WILL DIG ACROSS UTAH THIS
EVENING AND INTO THE FOUR CORNERS AREA TONIGHT.

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

EXPECT IFR -SN/SN LOCAL AREAS OF LIFR SN+/SN TO CONTINUE IN THE
UPSLOPE FAVORED AREAS VCNTY KLND-KCPR THROUGH AT LEAST EARLY THIS
EVENING. WIDESPREAD IFR/MVFR CONDITIONS IN -SN/CIGS/MTN
OBSCURATIONS TO CONTINUE THROUGH EASTERN SWEETWATER COUNTY TONIGHT. NORTH
OF KRIW AND KCPR...EXPECT GRADUALLY IMPROVING CONDITIONS FROM THE
NORTH TONIGHT. AREAS OF GUSTY NORTH WINDS 15-20KTS WITH GUSTS TO
30KTS AND AREAS OF BLSN CAN ALSO BE EXPECTED THROUGH EARLY THIS
EVENING. THE LAST AREAS TO SHOW IMPROVEMENT WILL BE UPSLOPE
FAVORED AREAS VCNTY KLND-KCPR WHERE AREAS OF IFR CIGS AND VSBY IN
-SN ARE EXPECTED TO PERSIST THROUGH 12Z FRIDAY. LCL MVFR
CONDITIONS DUE TO CIGS ARE EXPECTED THROUGH FRIDAY.

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

THROUGH 06Z TONIGHT EXPECT WIDESPREAD IFR -SN/SN...MTNS OBSCD...PREVAILING
VCNTY AND SOUTH OF A KEVW-KBPI- KPNA LINE. A NORTHEAST FLOW WILL
BRING DOWNSLOPE WINDS AND IMPROVING CONDITIONS ACROSS THE
NORTHWEST TO VCNTY KJAC AND KPNA THIS EVENING.

ALONG THE INTERSTATE 80 CORRIDOR AND VCNTY KRKS...STRONG NORTHEAST
WINDS CONTINUE THROUGH 06Z TONIGHT. WIDESPREAD IFR -SN/SN/BLSN WILL
CONTINUE THROUGH 06Z AS WELL. THESE CONDITIONS WILL LIKELY
PERSIST IN SOME AREAS WELL INTO TONIGHT WITH SOME IMPROVEMENT
EXPECTED BY EARLY FRIDAY MORNING.

&&

.FIRE WEATHER...

WIDESPREAD SNOW AND GUSTY WIND THROUGH TONIGHT SOUTH OF A CASPER
TO LANDER TO WESTERN SWEETWATER COUNTY LINE. EXPECT IMPROVING
CONDITIONS FROM NORTH TO SOUTH TONIGHT NORTH OF THIS AREAS. MOSTLY
DRY CONDITIONS ARE EXPECTED FRIDAY. BASINS AND VALLEYS WILL
DEVELOP INVERSIONS FOR FRIDAY NIGHT THAT WILL LEAD TO POOR MIXING
AND SMOKE DISPERSAL. ON SATURDAY...MILDER AIR MOVES IN ALONG WITH
SOME STRONGER WINDS THAT WILL ENCOURAGE SOME MIXING. ANOTHER SNOW
STORM IS POSSIBLE ON SATURDAY NIGHT IN THE WEST AND SPREADING EAST
OF THE DIVIDE SUNDAY.


&&

.RIW WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WARNING UNTIL 11 PM MST THIS EVENING
WYZ015-017>020-022-027>030.

WINTER WEATHER ADVISORY UNTIL 8 PM MST THIS EVENING
WYZ001>004-006-008>014-016-023>026.

WINTER STORM WARNING UNTIL 8 PM MST THIS EVENING WYZ005-007.

&&

$$

SHORT TERM...LIPSON
LONG TERM...C.BAKER
AVIATION...LIPSON
FIRE WEATHER...LIPSON




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