Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 132224 CCA
AFDRIW

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

.SHORT TERM...TONIGHT THROUGH MONDAY

SNOW WILL RAPIDLY DECREASE THIS EVENING AS THE UPPER LEVEL TROUGH
MOVES EAST AND DRY COLD AIR ALOFT MOVES IN. WITH CLEARING...LOW
STRATUS AND FOG IS EXPECTED TO FORM OVER THE FRESH WET SNOW COVER
IN THE VALLEYS AND BASINS. TEMPERATURES WILL BE MUCH COLDER AND
PARTS OF YELLOWSTONE NATIONAL PARK WILL DROP TO ZERO TO 5 BELOW
ZERO. AFTER AREAS OF MORNING FOG AND STRATUS...CLEARING IS
EXPECTED WITH SLIGHTLY WARMER TEMPERATURES IN THE AFTERNOON.

.LONG TERM...MONDAY NIGHT THROUGH SUNDAY

MONDAY NIGHT...WAA ASSOCIATE WITH A RIDGE BUILDING TO OUR WEST WILL
ENCOURAGE FOG FORMATION IN BASINS AND VALLEYS AS THE FRESH SNOW
COVER LEAVES BEHIND A MOIST BOUNDARY LAYER AND LIGHT SURFACE WINDS.
OTHERWISE...JUST A FEW HIGH CLOUDS SHOULD NOT PREVENT VIEWING OF THE
LUNAR ECLIPSE.

ANOTHER STORM SYSTEM MOVING INTO THE NORTHWEST IS LOOKING MORE AND
MORE LIKELY BY TUESDAY AFTERNOON...THE SYSTEM LOOKED LIKE IT WAS
JUST GOING TO GRAZE THE NORTHERN THIRD OF THE REGION WEDNESDAY BUT
NOW THE MODELS ARE TRYING TO DIG THE UPPER LEVEL TROUGH A BIT MORE
AS WELL AS BUILD A HIGH IN FROM CANADA AT THE SURFACE AS LOW
PRESSURE DEVELOPS IN EASTERN COLORADO...WHICH WOULD BE A VERY
FAVORABLE SET UP FOR YET ANOTHER UPSLOPE SNOW EVENT EAST OF THE
DIVIDE. QUITE A CHANGE FOR THE GFS OVER THE PAST 24 HOURS...WHICH
WOULD NORMALLY LEAD TO US DISCOUNTING THE SOLUTION BUT NOW IT LOOKS
LIKE THE EUROPEAN IS IN DECENT AGREEMENT ON THIS OUTCOME. THE SYSTEM
SHOULD MOVE OUT ON THURSDAY TAKING THE PRECIP WITH IT FOR THE MOST
PART. THE MODELS DIVERGE QUITE A BIT AFTER THURSDAY WITH THE GFS
ADVERTISING STRONG COLD CORE CYCLOGENESIS IN THE PLAINS WITH SOME
COOL AIR AND SHOWERS HANGING AROUND WYOMING WHILE THE EUROPEAN KEEPS
THE FLOW ZONAL WITH MILD AIR STARTING TO BUILD IN FROM THE
SOUTH...TRENDING WARMER WHEN COMPARED WITH THE PREVIOUS SOLUTIONS.

AS FOR NEXT FRIDAY...ALL GLOBAL MODELS WERE BRINGING ANOTHER STORM
SYSTEM INTO THE REGION...NOW IT APPEARS AS THOUGH IT IS WEAKER AND
MAY BE DELAYED UNTIL SATURDAY. GIVEN THE CHAOS IN THE MODELS RUN TO
RUN AND MODEL TO MODEL...CONTINUITY WAS KEPT WITH THE PREVIOUS
FORECAST FOR NOW.

&&

.AVIATION.../00Z 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 COME TO AN END. THESE CONDITIONS MAY
BRING BRIEF IFR TO MVFR CONDITIONS TO KJAC...KAFO...KEMM...
KPNA...KBPI AND KRKS UNTIL 03Z. THIS WILL BRING 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 UNTIL
18Z...THEN VFR CONDITIONS WILL PREVAIL.

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 COME TO AN END. THESE CONDITIONS
MAY BRING BRIEF IFR TO MVFR CONDITIONS TO THE AIRPORTS WITH
IMPROVEMENT IN THE NORTHWEST FIRST SPREADING SOUTHEAST 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 UNTIL 18Z...THEN VFR CONDITIONS WILL PREVAIL.

&&

.FIRE WEATHER...

SNOW WILL RAPIDLY DECREASE THIS EVENING AS THE UPPER LEVEL TROUGH
MOVES EAST AND DRY COLD AIR ALOFT MOVES IN. WITH CLEARING...LOW
STRATUS AND FOG IS EXPECTED TO FORM OVER THE FRESH WET SNOW COVER
IN THE VALLEYS AND BASINS. TEMPERATURES WILL BE MUCH COLDER AND
PARTS OF YELLOWSTONE NATIONAL PARK WILL DROP TO ZERO TO 5 BELOW
ZERO. AFTER AREAS OF MORNING FOG AND STRATUS...CLEARING IS
EXPECTED WITH SLIGHTLY WARMER TEMPERATURES IN THE AFTERNOON.
WITH A COLD AND STABLE AIR MASS...MIXING HEIGHTS WILL BE LOW AND
WITH DECREASING WINDS...SMOKE DISPERSAL IS EXPECTED TO BE POOR.

&&

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

$$

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











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