Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 131820
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1220 PM MDT SUN APR 13 2014

.SHORT TERM...SUNDAY THROUGH TUESDAY NIGHT

THE WINTER STORM IS ONGOING AND SO FAR THINGS ARE WORKING OUT FAIRLY
WELL. THERE HAVE BEEN A BIT MORE JET DYNAMICS THEN WE THOUGHT
YESTERDAY. SOME DECENT SNOW IS ASSOCIATION WITH THE RIGHT REAR QUAD
OF THE JET HAS BEEN ONGOING ACROSS THE EASTERN BIG HORN BASIN. AS A
RESULT WE HAVE INCREASED ACCUMULATIONS IN THOSE AREAS ALTHOUGH WE
KEPT ACCUMULATIONS IN THE ADVISORY LEVEL ALTHOUGH A FEW AREAS COULD
COME IN WITH HIGHER AMOUNTS. THE BEST OF THE DYNAMIC INDUCED SNOW
SHOULD END BY SUNDAY MORNING AS THE BEST UPPER LEVEL ENERGY MOVES
AWAY TO THE EAST. THEN AS LEE CYCLOGENESIS OCCURS OVER EASTERN
COLORADO WE WILL BEGIN TO SEE MORE NORTHEASTERLY UPSLOPE FLOW
DEVELOP. THIS SHOULD SHIFT THE HEAVIEST SNOW TO AREAS FROM THE WIND
RIVER RANGE THROUGH NATRONA COUNTY LATER TONIGHT AND INTO SUNDAY
MORNING. THE HIGHLIGHTS ISSUED LOOK FAIRLY REASONABLE AND AS A
RESULT WE WILL MAKE FEW CHANGES TO THEM AT THIS TIME. ALL MODELS
INDICATE SNOW CONTINUING INTO THE MORNING HOURS AND THEN TAPERING
OFF FROM NORTH TO SOUTH AS LOW PRESSURE MOVES AWAY TO THE EAST IN
THE AFTERNOON AND EVENING. MEANWHILE...OUT WEST ANOTHER PIECE OF
ENERGY WILL DROP SOUTH AND BRING SOME SOME PRECIPITATION TO THESE
AREAS AS WELL. HERE IT WILL BE MAINLY ON EASTERN FACING
SLOPES...ESPECIALLY IN THE SALT AND WYOMING RANGE AND TETONS WHERE A
FEW INCHES OF SNOW IS CERTAINLY POSSIBLE. ALL SNOW SHOULD COME TO AN
END TONIGHT AS HIGH PRESSURE BUILDS INTO THE AREA. WITH THE WET SNOW
AROUND THERE COULD BE SOME FOG AS WELL SO WE ADDED THAT FOR LATE
TONIGHT.

HIGH PRESSURE LOOKS TO CONTROL THE WEATHER FOR MONDAY AND BRING A
MAINLY DRY DAY WITH A MIXTURE OF SUNSHINE AND HIGH CLOUDS.
TEMPERATURES WILL BE BELOW NORMAL IN MANY AREAS WITH THE FRESH
SNOW PACK. AND EVEN WITH THE STRONG MID APRIL SUN MOST OF THE
RADIATION WILL GO TOWARD MELTING THE SNOW. WITH THE MELTING SNOW AND
A MAINLY CLEAR SKY AT NIGHT WE WILL LIKELY SEE FOG ONCE AGAIN REFORM
ACROSS THE AREA.

THE BREAK IN THE WEATHER WILL LIKELY NOT LAST LONG AS THE NEXT
SYSTEM MOVES IN FROM THE NORTH AND WEST. PRECIPITATION SHOULD BEGIN
SPREADING INTO WESTERN AREAS ON TUESDAY AFTERNOON AND POSSIBLY
SPREADING ACROSS MUCH OF THE AREA AT NIGHT. GIVEN THE CURRENT
STORM...WE DID NOT HAVE TIME TO TAKE A CLOSE LOOK AT IT SO WE LEFT
CONTINUITY ALONE FOR THE MOST PART. IT LOOKS TO BE WARMER AND BREEZY
DAY EAST OF THE DIVIDE WITH DOWN SLOPING WESTERLY FLOW DEVELOPING.
THE GFS SHOWS SOME 700 MILLIBAR WINDS RISING TO 50 KNOTS TUESDAY
AFTERNOON SO THIS WILL HAVE TO BE WATCHED FOR POSSIBLE HIGH WIND
HIGHLIGHTS. BUT...WE WILL CROSS THAT BRIDGE WHEN WE GET TO IT.

.LONG TERM...WEDNESDAY THROUGH SUNDAY

THE GFS MODEL HAS A WEATHER SYSTEM MOVING THROUGH WEDNESDAY. THE
ECMWF IS NOT AS BULLISH BUT STILL HAS SOME PRECIP MOVING THROUGH THE
AREA. THE GEM MODEL IS MORE LIKE THE GFS. WILL KEEP SNOW IN THE
FORECAST WED. BEST PRECIP CHANCE EAST OF THE DIVIDE IF THE CURRENT
TRACK HOLDS. WILL LOWER HIGH TEMPS EVEN MORE FOR WED. HOPEFULLY
MODELS WILL NOT CHANGE THEIR MIND IN THE COMING DAYS AS THIS PATTERN
IS WELCOME AS IT HAS BEEN A BIT DRY IN APRIL EAST OF THE DIVIDE.
PRECIP TO END AT THE LOWER ELEVATIONS WED EVENING WITH SOME SNOW
SHOWERS LINGERING IN THE MOUNTAINS LATE WED NIGHT. NW FLOW ALOFT FOR
THURSDAY WITH SOME MOUNTAIN SNOW SHOWERS. NOT MUCH MORE THAN
ISOLATED SHOWERS AT THE LOWER ELEVATIONS THURSDAY. MOSTLY DRY
THURSDAY NIGHT. ON FRIDAY A FAST MOVING WEATHER SYSTEM IN A WEST
FLOW ALOFT PASSES THROUGH MONTANA AND CLIPS THE NORTHERN MOUNTAINS
WITH SOME SHOWERS. ISOLATED SHOWERS FOR THE LOWER ELEVATIONS OF
THE FAR NORTH FRIDAY AFTERNOON AND EARLY EVE. GFS SHOWS ANOTHER
FAST MOVING WEATHER DISTURBANCE MOVING THROUGH ON SATURDAY WITH
MOUNTAIN SHOWERS AND ISOLATED ACTIVITY LOWER ELEVATIONS OF THE FAR
WEST. THE ECMWF/GEM MODELS ARE DRY SATURDAY. WILL PUT LOW PRECIP
CHANCE IN THE FAR WEST MOUNTAINS FOR NOW. NEXT SUNDAY LOOKS DRY AT
THIS TIME FOR MOST PLACES. ISOLATED SHOWERS FAR WEST MOUNTAINS
NEXT SUNDAY AFTERNOON WILL BE ADDED. HIGH TEMPS WILL MODERATE
THURSDAY...THEN SEASONAL APRIL HIGH TEMPS FRIDAY THROUGH SUNDAY.

.AVIATION.../18Z ISSUANCE/

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

AS AN UPPER LEVEL TROUGH PASSES THROUGH THE WEST...WIDESPREAD
MOUNTAIN OBSCURATIONS IN IFR TO MVFR CEILINGS AND VISIBILITIES
REDUCED IN SNOW SHOWERS WILL REMAIN THROUGH 00Z.  THIS WILL BRING
PERIODS OF IFR TO MVFR CONDITIONS TO KJAC...KAFO...KEMM...KPNA
AND BRIEFLY AT KBPI AND KRKS.  THE TROUGH WILL PASS EAST AROUND
00Z WITH PARTIAL CLEARING AND A SIGNIFICANT DECREASE IN PRECIPITATION
WITH SOME LINGERING SHOWERS OVER THE MOUNTAINS THROUGH 12Z.  WITH CLEARING
AREAS OF FOG WILL DEVELOP WITH INCREASING MVFR TO IFR CONDITIONS
SPREADING AFTER 08Z WITH LOW BROKEN STRATUS AND VISIBILITIES BELOW
A MILE IN FOG.  ANY OF THE AIRPORTS COULD END UP AFFECTED BY THE FOG.

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

AS AN UPPER LEVEL TROUGH PASSES THROUGH THE AREA...WIDESPREAD
MOUNTAIN OBSCURATIONS IN IFR TO MVFR CEILINGS AND VISIBILITIES
REDUCED IN SNOW SHOWERS WILL REMAIN THROUGH 00Z. THIS WILL BRING
PERIODS OF IFR TO MVFR CONDITIONS TO ALL OF THE AIRPORTS WITH
IMPROVEMENT IN THE NORTHWEST FIRST SPREADING SOUTHEAST FROM 21Z
THROUGH 03Z. THE TROUGH WILL PASS EAST BETWEEN 00Z AND 03Z WITH
PARTIAL CLEARING AND A SIGNIFICANT DECREASE IN PRECIPITATION WITH
SOME LINGERING SHOWERS OVER THE MOUNTAINS THROUGH 12Z. WITH
CLEARING AREAS OF FOG WILL DEVELOP WITH INCREASING MVFR TO IFR
CONDITIONS SPREADING AFTER 08Z WITH LOW BROKEN STRATUS AND
VISIBILITIES BELOW A MILE IN FOG. ANY OF THE AIRPORTS COULD END UP
AFFECTED BY THE FOG.

.FIRE WEATHER...

A STRONG WET COLD FRONT WILL BRING WIDESPREAD SNOW TO MUCH OF THE
AREA THIS AFTERNOON. SIGNIFICANT SNOW ACCUMULATIONS ARE
POSSIBLE...ESPECIALLY ALONG AND NEAR NORTH AND EAST FACING SLOPES.
THE SNOW WILL TAPER OFF SUNDAY AFTERNOON ENDING IN THE EVENING.
TEMPERATURES WILL BE MUCH COLDER THROUGH MONDAY. MIXING HEIGHTS
WILL BE VERY LOW WITH GENERALLY POOR SMOKE DISPERSAL. EXPECT DRY
WEATHER FROM LATE SUNDAY NIGHT THROUGH TUESDAY MORNING BEFORE THE
NEXT SYSTEM BRINGS THE NEXT CHANCE OF PRECIPITATION.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WARNING UNTIL 3 PM MDT THIS AFTERNOON
WYZ015-018>020-022.

WINTER WEATHER ADVISORY UNTIL 3 PM MDT THIS AFTERNOON
WYZ004>011-016-017.

&&

$$

SHORT TERM...HATTINGS
LONG TERM...AR
AVIATION...C.BAKER
FIRE WEATHER...HATTINGS







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