Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 220553
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1153 PM MDT Fri Apr 21 2017

.UPDATE...
Issued at 440 PM MDT Fri Apr 21 2017

Observations show the snow has changed to mainly rain across the
Cody Foothills with current temps in the mid to upper 30s. Could
see a change over back to snow tonight, but any accumulations will
be minor. Thus elected to cancel the winter weather advisory for
the Cody Foothills.

There is a PNS with rainfall and snowfall amounts. However most of
the data only goes through 9 AM this morning.

&&

.SHORT TERM...(This evening through Monday)
Issued at 220 PM MDT Fri Apr 21 2017

An upper level low pressure center over south central Wyoming
bringing widespread rain in the lower elevations with mountain
snow will gradually move east with showers tapering off from late
evening in the west to early morning in the east. Heaviest
snowfall expected in the Bighorn mountains where a winter storm
warning is in effect until early morning. Other mountain area
have winter weather advisories in effect until late evening. Cool
northwest flow aloft with limited moisture and instability will
bring scattered showers to the west tonight dissipating towards
morning. Snow line should be around 7800 feet. Local accumulations
of 1 to 3 inches are possible. High pressure will bring clearing
and lighter winds on Saturday and Saturday night. Sunday will see
increased moisture as the flow aloft over the west shifts to the
southwest with showers increasing Sunday afternoon through Monday
as winds increase.

.LONG TERM...(Monday night through Friday)
Issued at 220 PM MDT Fri Apr 21 2017

An unsettled weather pattern is still in store for the region
through the extended forecast period. A series of short waves are
expected to rotate east-northeast through the upper trough across
the region. This will result in timing issues related to the weather
systems expected to move across the western U.S. in the westerly
upper flow aloft. Areas generally west of the Divide will likely see
a combination of rain and snow in various periods through the
Wednesday and Friday time frame, with mainly snow expected above
7500 feet in the mountains. Due to the amount of moisture inflow in
the western Mountains and cooler temps especially above 8500 feet,
significant snow accumulations are possible through the Wednesday-
Friday period.

For areas east of the Divide, scattered showers will still spill
eastward into the region, with some locations not seeing much
precip, while others seeing some precip each day. Due to timing
issues, will need to update forecast and better time the
onset/ending of precip into the latter part of the extended forecast
later when timing issues are better determined. Expect temps to be
cooler next week generally at most locations due to the expected
increased clouds/precip.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1152 PM MDT Fri Apr 21 2017

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

Very patchy morning fog will be possible over western valleys.
Otherwise mainly SKC to some fair weather cumulus will be observed
today with mainly light winds. Tonight will see increasing cirrus
shield.

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

Improving conditions are expected between 09Z and 15Z in the lower
elevations as the rain showers end, and ceilings lift to low VFR
levels, or scatter out. Northern Johnson County and Bighorn
Mountains including KBYG could see MVFR ceilings linger through
early afternoon. Some areas that clear out during the predawn hours,
mainly over the Wind River Basin, and western Big Horn Basin could
see some fog development. This should also lift/scatter out by
around 15Z. Otherwise fair weather cumulus, and mainly light winds.
Tonight, increasing wind or LLWS in the wind corridor and on the lee
side of mountain ranges, as well as increasing cirrus.


&&

.FIRE WEATHER...
Issued AT 220 PM MDT Fri Apr 21 2017

An upper level low pressure center over south central Wyoming
bringing widespread rain in the lower elevations with mountain
snow will gradually move east with showers tapering off from late
evening in the west to early morning in the east. Heaviest
snowfall expected in the Bighorn mountains where a winter storm
warning is in effect until early morning. Other mountain area have
winter weather advisories in effect until late evening. Cool
northwest flow aloft with limited moisture and instability will
bring scattered showers to the west tonight dissipating towards
morning. Snow line should be around 7800 feet. Local accumulations
of 1 to 3 inches are possible. High pressure will bring clearing
and lighter winds on Saturday and Saturday night. Sunday will see
increased moisture as the flow aloft over the west shifts to the
southwest with showers increasing Sunday afternoon through Monday
as winds increase. The areas with precipitation and low clouds
continuing in the east on Saturday will have poor smoke dispersal
with low mixing heights, while the rest of the area with clearing
will have much improved mixing with sufficient transport winds
for good or better smoke dispersal. Transport winds will decrease
with high pressure building in on Sunday but overall mixing
heights will be favorable for good smoke dispersal.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...

Winter Storm Warning until 6 AM MDT Saturday for WYZ008-009.

&&

$$

UPDATE...Murrell
SHORT TERM...Baker
LONG TERM...Troutman
AVIATION...Troutman
FIRE WEATHER...Baker



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