Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 150552
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1052 PM MST Tue Feb 14 2017

.Short Term...Tonight Through Friday

High pressure will remain over western and central Wyoming
tonight into Wednesday night. Wind will gradually increase and
clouds will begin to increase in Late Wednesday night. The
increase in clouds and wind will be much more noticeable Thursday
with areas of snow, possibly rain in the valleys, in the west
during the afternoon. Southwest wind will become strong and gusty
over and near the mountains especially on the lee slopes and
through the wind corridor from Rock Springs to Casper area.
Thursday night and Friday snowfall will become more widespread
across the west and north mountains with accumulations of 4 to 6
inches in the mountains and 2 to 3 inches in the western valleys.
warming and windy with mostly cloudy conditions east of the
continental divide.

Two areas of ice jam flooding occurring. Bighorn river ice jamming
has moved north of Worland main threats now to Manderson, Basin
and Greybull as ice breaks up. Second area on Blacks Fork river
in western Sweetwater potential impact to Granger, but mainly
pasture land.

.Long Term...Friday Night Through Tuesday

A shortwave ridge will build over WY Friday night, as a closed low
digs southward toward the Desert Southwest and northern Mexico. This
will bring the next round of precipitation to the far west and other
areas west of the Continental Divide. The pattern will also split
again, as the low digs and closes off. The northern branch of the
PFJ will then become established by 00Z Mon and bring a shortwave
trough into phase with the closed upper low (now over northern
Mexico, SW of El Paso). This shortwave will be the first in a series
of shortwaves to impact western WY, from Sunday night through
Tuesday night, as a steady stream of Pacific moisture moves over the
Great Basin and WY. The best chances for snow will occur during this
time frame, with light to periods of moderate and heavy snow, mainly
impacting areas west of the Divide. Some of this will spill over
into the Upper Wind River Basin near Dubois, as well as isolated
activity near the east slopes of the Wind Rivers and Absarokas and
Natrona and southern Fremont counties.

Gusty southwest winds will also return to the Wind Corridor,
starting Saturday afternoon. These winds will mainly be an issue
during the afternoon hours, as 30-40kt h7 winds enter the area. A
weak leeside trough will also redevelop over eastern WY to slightly
tighten the pressure gradient in the area. A cold front will move
through the area Monday, cooling h7 temperatures briefly.
Temperatures are not expected to be extremely warm for mid-February,
but afternoon highs in the 50s for Johnson and Natrona counties are
expected to continue Saturday and Sunday. As was mentioned
yesterday, any effects from snow melt are not expected to impact
these areas.

&&

.Aviation.../06Z Issuance/

Patchy morning fog in the valleys and basins. Boundary layer
moisture is on the dry side, so not expecting widespread fog. The
best chance for fog Wednesday morning will be across the Big Horn
Basin along the Big Horn River. Otherwise, VFR conditions with
mainly clear skies are expected today. Increasing mid to high level
cloudiness is expected late Wednesday night over the west. Winds
will be light in most areas, but breezy to windy west to southwest
wind is expected from the Red Desert/South Pass area to Casper,
Dubois area, and on lee side of mountain ranges. Low-level wind
shear will be an issue at KCOD through the period, and could become
an issue at KJAC Wednesday night.

&&

.Fire Weather...

High pressure will remain over western and central Wyoming
tonight into Wednesday night. Wind will gradually increase and
clouds will begin to increase in Late Wednesday night. The
increase in clouds and wind will be much more noticeable Thursday
with areas of snow, possibly rain in the valleys, in the west
during the afternoon. Southwest wind will become strong and gusty
over and near the mountains especially on the lee slopes and
through the wind corridor from Rock Springs to Casper area.
Thursday night and Friday snowfall will become more widespread
across the west and north mountains with accumulations of 4 to 6
inches in the mountains and 2 to 3 inches in the western valleys.
warming and windy with mostly cloudy conditions east of the
continental divide. Areas with light wind will have poor mixing
and poor smoke dispersal through Friday. Windy areas with better
mixing will see fair to low end good smoke dispersal in the
afternoons.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...None.

&&

$$

SHORT TERM...C.Baker
LONG TERM...LaVoie
AVIATION...WM
FIRE WEATHER...C.Baker



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