Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 120551
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1150 PM MDT FRI APR 11 2014

.SHORT TERM...TONIGHT THROUGH SATURDAY

MILD BUT BREEZY WESTERLY FLOW THIS EVENING AS A SHORT WAVE ZIPS
BY TO THE NORTH OVERNIGHT. THIS SHORT WAVE WILL KICK DOWN A WEAK
COLD FRONT TONIGHT. ITS MAIN IMPACT WILL BE A WIND SHIFT AND SOME
COOLER TEMPERATURES TONIGHT INTO SATURDAY...ESPECIALLY ACROSS
NORTHERN WYOMING. SOME WEAK INSTABILITY ARRIVES AHEAD OF THE
TROUGH TOMORROW...KICKING OFF A FEW SHOWERS AND THUNDERSTORMS
IN THE AFTERNOON ON SATURDAY...ESPECIALLY SOUTH AND WEST OF WHERE
THE FRONT WASHES OUT ALONG THE DIVIDE.

.LONG TERM...SATURDAY NIGHT THROUGH FRIDAY

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.  BOTTOM LINE HAVE ISSUED A WINTER STORM
WATCH 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.  SOME SHOWERS AND CLOUDS WILL LIKELY LINGER THROUGH
SUNDAY EVENING THEN PARTIAL CLEARING IS EXPECTED.  MONDAY MORNING
EXPECTED TO BE COLD WITH POSSIBLE FOG OVER FRESH WET SNOW COVER.
DRY AND WARMER PERIOD THEN EXPECTED MONDAY THROUGH TUESDAY WITH SOME
SHOWERS DEVELOPING IN THE FAR NORTH TUESDAY AFTERNOON AND EVENING.
WEAK COLD FRONT AND SCATTERED SHOWERS EXPECTED TO SPREAD SOUTH
THROUGH TUESDAY NIGHT AND WEDNESDAY WITH FRONT BECOMING QUASISTATIONARY
ALONG OR NEAR THE CONTINENTAL DIVIDE.  THE FRONT IS THEN EXPECTED TO
REMAIN ACTIVE THROUGH WEDNESDAY NIGHT...DECREASING THROUGH THURSDAY
WITH DOWNSLOPE WINDS PRODUCING DRYING AND WARMING WHICH IS EXPECTED
TO CONTINUE THROUGH FRIDAY MORNING BEFORE ANOTHER PACIFIC TROUGH
MOVES IN PRODUCING INCREASED SHOWERS IN THE WEST AND NORTH FRIDAY
AFTERNOON.

&&

.AVIATION.../06Z ISSUANCE/

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

VFR CONDITIONS WILL PREVAIL THROUGH 20Z SATURDAY.  INCREASING
MOISTURE AND INSTABILITY WILL INITIALLY BRING SCT SHRA AND ISOLD
TSRA VCNTY AND SOUTH OF INTERSTATE 80 AND INTO THE NW CORNER OF
WYOMING AFTER 20Z SATURDAY.  A COLD FRONT WILL SPREAD NMRS SHSN AND
WIDESPREAD MTN OBSCURATIONS SOUTH FROM MONTANA TO A VCNTY KJAC-KDUB
LINE BTWN 0Z-6Z SUNDAY.  HOWEVER INCREASING NE DOWNSLOPE FLOW WILL
RESULT IN SOME IMPROVEMENT ACROSS THE NW AFTER 06Z.  RAIN AND SNOW
...WIDESPREAD IFR/LIFR CONDITIONS...WILL DEVELOP PRIMARILY FROM KRKS
TO THE SOUTH PASS AREA 6Z-12Z SUNDAY AS THE COLD FRONT BACKS INTO SW
WYOMING.

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

VFR CONDITIONS WILL PREVAIL ACROSS THE AREA THROUGH 21Z SATURDAY
WITH A PREVAILING N-NE SFC FLOW DEVELOPING THROUGH THE MORNING.
WIDESPREAD RAIN AND SNOW WILL RAPIDLY DEVELOP ACROSS THE NORTH AFTER
21Z SATURDAY AND SPREAD SOUTH THROUGH THE EVENING.  THE RAIN OR
RAIN/SNOW MIX WITH MVFR/IFR CONDITIONS WILL LAST A COUPLE OF HOURS
WITH THE INITIAL FRONTAL BAND WITH SNOW LEVELS RAPIDLY LOWERING
BEHIND THE FRONT.  EXPECT WIDESPREAD IFR/LIFR CONDITIONS VCNTY AND
NORTH OF A KCOD-KBYG LINE BY 00Z SUNDAY SPREADING TO A VCNTY
KLND-KCPR LINE BETWEEN 05Z-08Z SUNDAY.


&&

.FIRE WEATHER...

A DRY COLD FRONT WILL DROP SOUTHWARD EAST OF THE DIVIDE TONIGHT
WITH LITTLE IMPACT ASIDE FROM A WIND SHIFT AND COOLER
TEMPERATURES...IT WILL WASH OUT ALONG THE DIVIDE EARLY SATURDAY.
A FEW THUNDERSTORMS ARE POSSIBLE AHEAD OF THE NEXT COLD FRONT
DROPPING SOUTH SATURDAY...ESPECIALLY OVER THE HIGHER TERRAIN
ACROSS THE NORTH AND ALONG RAWLINS DISPATCH AREA. THE NEXT COLD
FRONT WILL BRING WETTING RAIN AND/OR SNOW TO MUCH OF THE FORECAST
AREA ALONG AND EAST OF THE DIVIDE SATURDAY NIGHT AND SUNDAY.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WATCH FROM SATURDAY EVENING THROUGH SUNDAY
AFTERNOON WYZ002-003-005>011-015>020-022.

&&

$$

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










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