Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 182228
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
328 PM MST THU DEC 18 2014

.SHORT TERM...TONIGHT THROUGH FRIDAY

WV IMAGERY SHOWING WEAK NW FLOW OVERHEAD...WITH AN EXITING VERY WEAK
UPR WAVE...AND A SLIGHTLY STRONGER SW TROF ORIENTED N/S JUST TO THE
WEST OF WY...AND A SW RIDGE JUST TO THE WEST OF THIS FEATURE.
WEAK/MODEST MID LVL MOISTURE ENTERING THE STATE FROM THE WEST. SFC
PATTERN CONTINUES ON THE WEAK SIDE WITH DIFFUSE SFC TROF ACROSS ERN
WY...WEAK HIGH P OVER THE WEST. RELATIVELY WEAK FORCING AT ALL
LEVELS ALSO CONTINUES...WHICH CONTINUES TO DELAY THE DEPARTURE OF
THE EMBEDDED FOG/STRATUS DECK OVR CNTRL FREMONT COUNTY.

WEAK UPR WAVE IS HELPING A BIT THIS MORNING/EARLY AFTERNOON AS SOME
FLURRY/LIGHT SNOW IS PRECIPITATING OUT OF THE FOG/STATUS OVR CNTRL
FREMONT...IMPROVING VISIBILITIES TO AS MUCH AS 3 MILES. STILL
WAITING FOR CLOUD BASES TO RISE JUST A BIT. HOPING TO DRY THIS CLOUD
OUT JUST ENOUGH THAT TONIGHT`S SW TROF COMING IN FROM ID WILL HELP
PRECIPITATE OUT THE REST AND CLEAR THE SKIES. HOWEVER...CONTINUED
WEAK FLOW BETWEEN THESE TWO SMALL SYSTEMS...FROM SFC ON UP...IS NOT
HELPING. SO IF CLOUDS DON`T COMPLETELY DISSIPATE IN THIS
AREA...ANOTHER QUICK RETURN TO AT LEAST PATCHY DENSE FOG CAN BE
EXPECTED ONCE AGAIN. WILL DECIDE LATER THIS AFTERNOON WHETHER OR NOT
TO EXPIRE OR EXTEND CURRENT DENSE FOG ADVISORY FOR ZONE 17. IF THE
ATMOSPHERE CAN NOT GET RID OF IT TODAY/TONIGHT...IT WILL LIKELY BE
AROUND UNTIL SATURDAY MORNING. PATCHY FOG ALSO POSSIBLE OVR NRN
SWEETWATER...PERHAPS EXTREME SRN FREMONT COUNTIES.

OTHERWISE...WEAK SW TROF TONIGHT GETS CHASED OUT BY THE
AFOREMENTIONED SW RIDGE CURRENTLY OVR THE WEST COAST. AGAIN...WEAK
TO MODEST MID LVL MOISTURE FLOWING INTO THE WRN MOUNTAINS THROUGH
THE FCST PERIOD...EVEN WITH THE RIDGING GOING ON...WILL OFFER
CONTINUOUS TERRAIN LIFTED LIGHT SNOW/FLURRIES OVR THE MOUNTAINS OF
THE WEST...WITH PERHAPS 1 TO 3 INCHES OF NEW ACCUMULATION BETWEEN
TONIGHT AND FRIDAY NIGHT.

.LONG TERM...FRIDAY NIGHT THROUGH THURSDAY

SHORTWAVE RIDGING GIVES WAY TO W-NW FLOW ALOFT THIS UPCOMING WEEKEND.
THERE WILL BE A WEAK SHORTWAVE TO IMPACT THE WESTERN AND NORTHERN
MOUNTAINS OF WYOMING ON SATURDAY WITH AREAS OF SNOW. MOST OF THIS
SNOW SHOULD BE CONFINED TO THE HIGHER MOUNTAINS. BREEZY AND DRY
FOR REMAINDER OF FORECAST AREA SATURDAY INTO SATURDAY EVENING.

THE FLOW ALOFT STRENGTHENS IN RESPONSE TO A VERY STRONG JET
DIGGING FROM THE PACIFIC NORTHWEST. THE EXIT REGION OF THIS JET
MOVES OVER WESTERN WYOMING BY SUNDAY AFTERNOON. THIS WILL ENHANCE
BOTH THE MOISTURE AND LIFT FOR ALL OF WESTERN WYOMING SUNDAY
AFTERNOON INTO MONDAY. A LONG DURATION OF MODERATE TO HEAVY
SNOWFALL IS LIKELY TO OCCUR AND WILL IMPACT THE TETONS AND
YELLOWSTONE NATIONAL PARK. THIS ALSO INCLUDES THE WESTERN VALLEYS
OF WYOMING...ALTHOUGH IT SHOULD BE A VERY WET SNOW.

THIS WILL ALSO TRANSLATE TO A HIGH WIND EVENT OVER AND EAST OF THE
DIVIDE...ESPECIALLY ALONG THE ABSAROKA RANGE AND CODY FOOTHILLS FOR
SUNDAY NIGHT INTO MONDAY. REGARDLESS...THIS LOOKS TO BE A POTENT
STORM BY THE END OF THIS WEEKEND. WILL CONTINUE TO MONITOR AND
PINPOINT SNOW AMOUNTS AND WIND SPEED RANGES OVER THE NEXT FEW SHIFTS.

SNOW AND WIND WILL CONTINUE FOR PORTIONS OF THE WEST AND NORTH
THROUGH EARLY TUESDAY. LOWER ELEVATIONS EAST OF THE DIVIDE WILL STAY
MOSTLY DRY THROUGH TUESDAY WITH SLIGHTLY ABOVE NORMAL TEMPERATURES.

WITH PRIMARY FOCUS ON THE POTENT STORM SYSTEM WEST OF THE DIVIDE...
IT IS BEST TO CAPTURE PREVIOUS FORECAST THOUGHTS REGARDING CHRISTMAS
EVE AND CHRISTMAS DAY...NEXT THURSDAY...FOR WEST CENTRAL WYOMING:
DETAILS WILL CONTINUE TO CHANGE BUT THE BOTTOM LINE CONTINUES TO BE
SNOW AND WIND OUT WEST TO START THE PERIOD WITH WIND EAST WITH SOME
RAIN/SNOW MAINLY NORTH AND SOUTH AND THEN TURNING SHARPLY COLDER
WITH A TRAVEL IMPACTING STORM EAST OF THE DIVIDE LATER CHRISTMAS EVE
THROUGH CHRISTMAS DAY. HOW MUCH SNOW WILL WILL BE DETERMINED AS WE
GET CLOSER BUT HIGHLIGHTS WILL PROBABLY BE NEEDED IN CENTRAL
WYOMING. BOTTOM LINE...VERY ACTIVE WEATHER WEEK AHEAD LEADING INTO A
MAJOR HOLIDAY.

&&

.AVIATION.../00Z ISSUANCE/

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

MVFR TO OCCASIONAL IFR CONDITIONS DUE TO SOME FOG AND LOW CLOUDS
WILL CONTINUE IN THE WIND RIVER BASIN...INCLUDING KRIW...THROUGH 15Z
FRI. THIS EVENING...A MINOR UPPER LEVEL DISTURBANCE WILL MOVE
THROUGH AND MAY POSSIBLY AID IN PRECIPITATING OUT THE REST OF THE
CLOUD/FOG DECK...AT WHICH POINT KRIW AIRPORT COULD SEE MVFR TO VFR
CONDITIONS BY LATE THIS EVENING. HOWEVER...IF THIS SCENARIO DOES NOT
PAN OUT...THEN PORTIONS OF THE CENTRAL WIND RIVER BASIN COULD BE
STUCK IN THE FOG AND LOW CIGS THROUGH SATURDAY MORNING.

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

VFR CONDITIONS WILL PREVAIL THROUGH THE FORECAST PERIOD AT ALL SITES
EXCEPT KJAC. KJAC WILL EXPERIENCE TEETER BETWEEN VFR/MVFR CEILINGS
AND VISIBILITY THROUGH 03Z...AT WHICH POINT CEILINGS WILL BECOME
PRIMARILY MVFR...REMAINING SO THROUGH THE REST OF THE FORECAST
PERIOD. THERE WILL ALSO BE INCREASING CHANCES FOR LIGHT SNOW AND
SOME FURTHER VIS REDUCTION AFTER 03Z. OTHERWISE...LIGHT SNOW WILL
OCCUR IN THE WESTERN MOUNTAINS TONIGHT THROUGH FRIDAY...WITH MVFR TO
IFR CONDITIONS AND FREQUENT MOUNTAIN OBSCURATION.

&&

.FIRE WEATHER...

WINTER CONTINUES ACROSS THE FORECAST AREA...KEEPING TEMPS ON THE
LOWER SIDE...AND RH VALUES ON THE HIGHER SIDE...WITH FIRE DANGER
REMAINING LOW FROM NOW THROUGH THE BEGINNING OF NEXT WEEK.
AGAIN...DUE TO THE COLDER NEAR SURFACE TEMPERATURES AND WEAK FLOW
ALOFT....POOR SMOKE DISPERSION CAN BE EXPECTED TO CONTINUE THROUGH
AT LEAST SATURDAY MORNING BEFORE BETTER MIXING STARTS TO OCCUR. A
LARGE VIGOROUS WINTER WEATHER SYSTEM IS POISED TO COME TOGETHER AND
IMPACT MOST OF THE DISPATCH ZONES BEGINNING SATURDAY NIGHT ACROSS
THE WEST...COVERING THE REST OF WYOMING BY LATER SUNDAY THROUGH
MONDAY. SIGNIFICANT SNOWFALL...AND STRONG WINDS...WILL BE POSSIBLE
WITH THIS STORM SYSTEM.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...NONE.
&&

$$

SHORT TERM...BRAUN
LONG TERM...KPL
AVIATION...BRAUN
FIRE WEATHER...BRAUN




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