Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 021828
AFDRIW

AREA FORECAST DISCUSSION...UPDATE
NATIONAL WEATHER SERVICE RIVERTON WY
1128 AM MST TUE FEB 2 2016

.SHORT TERM...TODAY THROUGH THURSDAY NIGHT

TODAY AND TONIGHT...GRADUAL DRYING AND SOME CLEARING AS OUR STORM
PULLS OUT INTO THE PLAINS WITH OCCASIONAL FLURRIES LEFTOVER INTO THE
AFTERNOON. CHILLY NORTHWEST FLOW WILL TAKEOVER WITH THE LAST FEW
MODEL RUNS BRINGING A WEAK DISTURBANCE THROUGH LATE...WITH LAPSE
RATES LOOKING MORE IMPRESSIVE...THOUGHT THE PREVIOUS SHIFT HAD A
GOOD HANDLE ON WHERE THE BEST CHANCE FOR SNOW SHOWERS WILL BE...WENT
AHEAD AND BUILT ON THAT IDEA POPS WISE AND BROUGHT THEM EARLIER INTO
THE EVENING AND AFTERNOON GIVEN THE FAVORABLE LAPSE RATES AND
ADEQUATE MOISTURE. IN ADDITION...WIND CHILLS BELOW ZERO ACROSS
WESTERN AND CENTRAL WYOMING...WITH SOME WIND CHILLS APPROACHING 20
BELOW ALONG THE INTERSTATE 80 CORRIDOR AND IN THE WESTERN MOUNTAINS
CAN BE EXPECTED.

WEDNESDAY...RIDGING BUILDS INTO THE REGION WITH SOME FLATTENING LATE
WEDNESDAY NIGHT. WAA AND DIFLUENT FLOW AHEAD OF AN APPROACHING SHORT
WAVE WILL INCREASE THE CHANCE FOR SNOW IN THE WESTERN MOUNTAINS
LATE...OTHERWISE WEDNESDAY WILL BE BREEZY...ESPECIALLY IN THE CODY
FOOTHILLS AND ACROSS THE SOUTH...AND COOL AS MILD AIR ALOFT TAKES
ITS TIME FILTERING IN FROM THE WEST.

THURSDAY...A SPLITTING TROUGH MOVES INTO THE REGION...DELIVERING
ANOTHER CHANCE FOR MEASURABLE SNOW ACROSS THE WEST AND SOUTH DURING
THE DAY...POSSIBLY MOVING EAST OF THE DIVIDE THURSDAY EVENING. THE
TRANSITION EAST OF THE DIVIDE IS HANDLED DIFFERENTLY BY THE
MODELS...SO JUST INTRODUCED SOME SLIGHT CHANCE POPS FOR NOW.

.LONG TERM...FRIDAY THROUGH TUESDAY

THERE MAY BE LINGERING LIGHT SNOW OR FLURRIES IN THE EAST ZONES
FRIDAY MORNING IF THE ECMWF MODEL IS CORRECT WHILE THE GFS IS DRY.
WILL OPT FOR A DRY FORECAST FRIDAY FOR NOW. SATURDAY LOOKS DRY AS
WELL FOR THE REGION. THE EXCEPTION IS NW WY WHERE SCATTERED LIGHT
SNOW DEVELOPS SATURDAY AFTERNOON AHEAD OF THE NEXT WEATHER SYSTEM.
MILDER HIGH TEMPS FRIDAY AND SATURDAY WITH SNOW COVERED AREAS NOT
RECOVERING AS MUCH DUE TO THE RECENT ADDITIONAL SNOW COVER. SUN
ANGLE MIGHT HELP BUT THAT EFFECT IS MORE POTENT IN LATE FEBRUARY.

THIS WEATHER SYSTEM IS FORECAST TO DROP SOUTHEAST THROUGH MONTANA
AND WY SATURDAY NIGHT AND SUNDAY. MUCH COLDER AIR FROM CANADA IS
DRAWN SOUTH WITH THIS SYSTEM AS WELL AS A POTENTIAL SECOND SHOT OF
COLD AIR SUNDAY NIGHT INTO MONDAY. THE 00Z GFS AND ECMWF MODEL
WERE IN AGREEMENT. THE 06Z GFS HAS BACKED OFF ON THE COLD FOR
MONDAY.

THERE ARE CERTAINLY MODEL ISSUES WITH RESPECT TO THE HIGH
AMPLITUDE RIDGE BUILDING OVER THE WEST COAST OF THE U.S. INTO
WESTERN CANADA SUNDAY THROUGH TUESDAY. THE 00Z ECMWF MODEL NUDGES
THE RIDGE CLOSER TO WY MONDAY INTO TUESDAY. THUS AFTER A COLD
SUNDAY...MONDAY AND TUESDAY ARE MILDER. THE 00Z GFS WAS KEEPING
THE COLD AIR IN ON SUNDAY AND MONDAY WITH MODERATION ON TUESDAY.
THE 06Z GFS GOES MUCH MILDER MONDAY AND TUESDAY LEANING TOWARD THE
00Z ECMWF. WITH ALL THAT SAID...HAVE COLDER HIGHS FOR SUNDAY. THEN
MONDAY WOULD BE A BIT WARMER IN THE WEST EXCEPT FOR THE SNOW
COVERED WESTERN VALLEYS WHERE INVERSIONS SET UP. MONDAY EAST OF
THE DIVIDE LOOKS COLDER BUT DID NOT GO AS COLD AS SOME GUIDANCE
SUGGESTS DUE TO THE UNCERTAINTY OF THE PATTERN. THEN MILDER ALL
AREAS TUESDAY WITH LESS WARMING IN THE SNOW COVERED VALLEYS.
AS FOR PRECIP...SCATTERED MOUNTAIN LIGHT SNOW SUNDAY WITH BETTER
COVERAGE IN THE NORTHERN BIGHORN MTS. MONDAY AND TUESDAY DRIER IN
THE WEST AND CENTRAL. POSSIBLE SCATTERED LIGHT SNOW IN THE
NORTHERN BIGHORN MTS AND NORTHERN JOHNSON COUNTY MONDAY...DRY ON
TUE.

PLENTY OF TIME TO WATCH THIS UPCOMING WEEKEND WEATHER PATTERN AND
ADJUST FORECAST AS NEEDED.

&&

.AVIATION.../18Z ISSUANCE/

THE SNOW AND MVFR/IFR/MTN OBSCTNS CONDITIONS ARE EXPECTED TO
GRADUALLY DECREASE IN COVERAGE DURING THE MORNING...WITH TERMINALS
BECOMING MAINLY VFR BY 21Z IN MOST AREAS...AS THE WINTER STORM
CONTINUES TO PULL AWAY FROM THE AREA. A WEAK SYSTEM IN THE NORTHWEST
FLOW IN WAKE OF THE MAIN SYSTEM COULD RESULT IN ISOLATED TO LOCALLY
SCATTERED SNOW SHOWERS TONIGHT...AND WILL HAVE VCSH TO ACCOUNT FOR
THIS ALTHOUGH KCPR COULD SEE BRIEF IFR/MVFR CONDITIONS. WINDS ARE
EXPECTED TO BE MAINLY LIGHT IN MOST AREAS TODAY. HOWEVER BREEZY WEST
TO NORTHWEST WINDS ARE EXPECTED TO DEVELOP TONIGHT OVER
SWEETWATER...UPPER GREEN RIVER BASIN...AND THE DUBOIS AREA. THIS
WIND COULD EVEN IMPACT THE KRIW TERMINAL. SOUTHWEST WINDS ARE
EXPECTED TO INCREASE AT KCPR BY 15Z WED ALONG WITH THE POTENTIAL FOR
REDUCED VISIBILITY IN BLOWING SNOW..

&&

.FIRE WEATHER...

SNOW SHOWERS ACROSS THE FORECAST AREA WILL RESULT IN FAIR SMOKE
DISPERSION THIS AFTERNOON. MIXING HEIGHTS LOWER A BIT AFTER TODAY
BUT VARIABLE CLOUD COVER AND OCCASIONAL BREEZES WILL KEEP SMOKE
DISPERSION FROM BOTTOMING OUT ACROSS THE BOARD...THOUGH THERE WILL
BE SOME INVERSIONS RETURNING TO VALLEYS AND BASINS AFTER
TONIGHT...WITH SOME IMPROVEMENT DURING THE DAY. THERE WILL BE A FEW
SHOTS AT SOME MORE SNOW AS THE WEEK MOVES ALONG BUT NOTHING
SIGNIFICANT ON THE HORIZON. A STRONG RIDGE COULD BE BUILDING IN NEXT
WEEK...WITH DRIER AND CALMER WEATHER POSSIBLE...IN ADDITION TO
SOME STRONG INVERSIONS IN ANY SNOW COVERED VALLEYS OR BASINS.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...

WINTER STORM WARNING UNTIL 9 AM MST THIS MORNING FOR WYZ020-022.

WINTER WEATHER ADVISORY UNTIL 9 AM MST THIS MORNING FOR WYZ011-
015-017>019-027>030.

&&

$$

SHORT TERM...ALLEN
LONG TERM...AR
AVIATION...WM/LIPSON
FIRE WEATHER...ALLEN


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