Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 130555
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1155 PM MDT SAT APR 12 2014

.SHORT TERM...TONIGHT THROUGH SUNDAY

AS AN UPPER LEVEL LOW PRESSURE TROUGH DIGS SOUTHEAST ACROSS IDAHO...
A COLD FRONT WILL MOVE SOUTH FROM MONTANA SATURDAY EVENING.  THE
UPPER TROUGH WILL PRODUCE FAIRLY STRONG UPPER DIVERGENCE OVER MUCH
OF WESTERN AND CENTRAL WYOMING...ESPECIALLY OVER THE COLD FRONT.
THE MID LEVELS WILL DESTABILIZE WITH INCREASING DEFORMATION AND
FRONTOGENETIC FORCES INCREASING THE BAROCLINICITY ALONG THE COLD
FRONT.  AHEAD OF THE COLD FRONT...DEEP CONVECTION WILL BE POSSIBLE
WITH A THREAT OF AT LEAST ISOLATED THUNDERSTORMS...EMBEDDED IN A
LARGER FIELD OF SHOWERS.  SMALL HAIL AND GUSTY WINDS MAY ACCOMPANY
THE THUNDERSTORMS WHICH WILL BE ACROSS CENTRAL AND SOUTHERN AREAS AS
WELL AS THE MOUNTAINS WEST OF THE CONTINENTAL DIVIDE.  BEHIND THE
COLD FRONT THE PRECIPITATION MAY START OUT AS RAIN EARLY IN THE
EVENING...BUT TEMPERATURES ALOFT COOL QUICKLY AND EXPECT A QUICK
CHANGE OVER TO SNOW.  THE SNOW SHOULD BE WET AROUND A 10 TO 1 RATIO
AND WITH SOME CONVECTIVE NATURE WITH AT LEAST MID LEVEL INSTABILITY
SUPPORTING LOW LEVEL CONVERGENCE...SNOWFALL RATES OF 1 TO 1.5 INCHES
AN HOUR ARE POSSIBLE.  THE STRONGEST PERIOD OF SNOWFALL SHOULD BE
FROM LATE EVENING TO EARLY MORNING SUNDAY...OR ABOUT 9 TO 10 HOURS
AND THIS SHOULD HELP DETERMINE ACCUMULATION POTENTIAL.  THERE WILL
LIKELY BE AN OROGRAPHIC COMPONENT TO THE SNOWFALL DISTRIBUTION WITH
HIGHER AMOUNTS IN THE NORTHERN BIGHORN MOUNTAINS...CASPER
MOUNTAIN...THE OWL CREEK AND BRIDGER RANGES AND THE EAST SLOPES OF THE
WIND RIVER RANGE EXTENDING EAST ALONG THE NORTH SLOPES OF THE
GRANITE AND GREEN MOUNTAINS. HAVE CONTINUED WIN STORM WARNINGS AND
ADVISORIES AS ISSUED FOR MUCH OF THE AREA EAST OF THE CONTINENTAL
DIVIDE FROM 03Z SUNDAY THROUGH 21Z SUNDAY. EXPECT ACCUMULATIONS TO
DECREASE FROM NOON TO 3 PM AND DRYING SPREADING SOUTH THROUGH THE
AFTERNOON AND SUNDAY EVENING.

.LONG TERM...SUNDAY NIGHT THROUGH SATURDAY

SLOW CLEARING FROM NORTH TO SOUTH SUNDAY NIGHT AS OUR WINTER STORM
EXITS INTO COLORADO. 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.

MODELS HAVE BEEN BACKING OFF ON A STRONGER RIDGE HOLDING ITS PLACE
OVER WYOMING ON TUESDAY...NOW THERE ARE SOME HINTS AT ANOTHER STORM
SYSTEM MOVING INTO THE NORTHWEST BY TUESDAY AFTERNOON AND THEN
GRAZES THE NORTHERN THIRD OF THE REGION WEDNESDAY WITH A SECONDARY
MOISTURE FEED MOVING INTO SOUTHERN WYOMING WITH SOME INSTABILITY
KICKING OFF SOME SHOWERS IN THE AFTERNOON ACROSS SWEETWATER COUNTY.
THE STRENGTH AND THE TRACK OF MAIN MOISTURE REMAINS UNCLEAR AS THE
GFS AND GEM MODELS HAVE BEEN MORE BULLISH THAN THE ECMWF...BUT THE
LATEST RUN IS BRINGING IT CLOSER INTO LINE WITH THE GFS. THE SYSTEM
MOVES OUT EARLY ON THURSDAY TAKING THE PRECIP WITH IT FOR THE MOST
PART. LINGERING MOUNTAIN SNOW SHOWERS ARE POSSIBLE AND ISOLATED
SHOWERS EAST OF THE DIVIDE BUT THURSDAY LOOKS DRY FOR MOST OF THE
REGION. THE MODELS DIVERGE QUITE A BIT AFTER THURSDAY WITH THE GFS
ADVERTISING STRONG 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.

AS FOR NEXT FRIDAY...ALL GLOBAL MODELS BRING ANOTHER STORM SYSTEM
INTO THE REGION...WITH VARIED TIMING AND STRENGTH. TEMPERATURES WILL
BE KEY AS SOME MODELS START THE PRECIP EARLY...AND WITH A MORE ZONAL
FLOW THAT COULD MEAN SOME RAIN FOR THE JACKSON AREA AND BAD NEWS FOR
THE LAND SLIDE...OTHERS DIG THE SYSTEM A BIT MORE AND BRING IN
SOUTHWEST FLOW AND COOLER TEMPERATURES...WHICH WOULD LEAN TOWARD
SNOW. WILL KEEP CONTINUITY AS THE PREVIOUS SHIFT HAS IT COVERED
PRETTY WELL...BRING IN LOW PRECIP CHANCE TO THE WEST THURS NIGHT.
THEN A BETTER CHANCE OF PRECIP FRIDAY AND FRI NIGHT OVER THE WEST.
WILL HAVE A LOW CHANCE OF PRECIP EAST OF THE DIVIDE FOR FRIDAY
AFTERNOON AND FRI NIGHT. NEXT SATURDAY LOOKS DRY FOR MOST
AREAS...ISOLATED SHOWERS IN THE WESTERN MOUNTAINS MAINLY FOR THE
AFTERNOON AND EVENING HOURS. HIGH TEMPS ON TUESDAY LOOK TO BE
MILDER...THEN COOLER ON WED DUE TO THE WEATHER SYSTEM. THURS LOOKS
TO WARM UP A LITTLE. FRI WILL BE A TAD MILDER EAST OF THE DIVIDE
AHEAD OF THE WEATHER SYSTEM WHILE THE WEST IS NEAR OR SLIGHTLY
COOLER TO THE THURS HIGHS.

&&

.AVIATION.../06Z ISSUANCE/

WEST OF THE DIVIDE...KJAC/KPNA/KBPI/KRKS ROUTES
A DRY SLOT WAS OVER THE WEST...KJAC/KPNA/KBPI...AT 06Z WITH A LINE
OF RAIN AND SNOW SHOWERS FROM VCNTY KIDA INTO THE NW CORNER OF
WYOMING AT 06Z.  THIS AREA OF -SHSN WILL MIGRATE SOUTH OVERNIGHT
BRINGING MVFR/IFR -SHSN INTO VCNTY KJAC AROUND 10Z AND TO KBPI AND
KPNA AROUND 14Z.

A STRENGTHENING NORTHEAST FLOW WILL BRING LOWERING CIGS...WIDESPREAD
IFR SHSN INTO VCNTY KRKS BY 12Z.  EXPECT WIDESPREAD MTN OBSCURATIONS
AND MVFR/IFR CONDITIONS IN -SN AT MOST TERMINALS THROUGH 18Z...AND
THEN GRADUAL IMPROVEMENT FROM NW-SE THROUGH THE AFTERNOON.  SKC
CONDITIONS WILL PREVAIL 06Z-12Z MONDAY.


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

WIDESPREAD IFR/LIFR CONDITIONS IN SN AND MTN OBSCURATIONS WILL
CONTINUE THROUGH 15Z SUNDAY ALONG WITH AREAS OF NORTH WIND AT 15-25KTS.
CONDITIONS WILL SLOWLY IMPROVE FROM THE NORTH IN THE LATE MORNING
AND AFTERNOON.  MVFR/IFR CONDITIONS IN SN WILL PERSIST LONGEST VCNTY
KLND/KCPR INTO THE AFTERNOON.  SKC CONDITIONS WILL PREVAIL ACROSS
THE REGION 06Z-12Z MONDAY.

&&

.FIRE WEATHER...

A STRONG WET COLD FRONT WILL BRING WIDESPREAD SNOW TO MUCH OF THE
AREA TONIGHT AND INTO SUNDAY 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.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WARNING FROM 9 PM THIS EVENING TO 3 PM MDT SUNDAY
WYZ015-018>020-022.

WINTER WEATHER ADVISORY FROM 9 PM THIS EVENING TO 3 PM MDT
SUNDAY WYZ004>007-010-011-016-017.

WINTER WEATHER ADVISORY FROM 6 PM THIS EVENING TO NOON MDT
SUNDAY WYZ002.

WINTER WEATHER ADVISORY FROM 6 PM THIS EVENING TO 3 PM MDT
SUNDAY WYZ008-009.

WINTER STORM WARNING FROM 6 PM THIS EVENING TO NOON MDT SUNDAY
WYZ003.

&&

$$

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










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