Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 140531

Area Forecast Discussion
National Weather Service Riverton WY
1031 PM MST Mon Feb 13 2017

.SHORT TERM...Tonight through Thursday

Satellite imagery shows split flow pattern, with the northern
branch moving into the Gulf of Alaska and the southern branch
moving over the West Coast into northern Mexico. Upstream ridge
continues to build over the Pacific Northwest and along the
Canadian West Coast. Area of low-level stratus/fog over western
Sweetwater County has shrunk south of Farson and Hwy 28 and is now
mainly confined to Green River/Little America southward.

Dense Fog Advisory may be necessary tonight for the above
mentioned area. Will wait another hour or so before deciding to
issue. Otherwise, patchy fog will be possible in the valleys and
basins tonight through Tue morning. Winds will be light across the
area through Tue. Sfc pressure gradient will increase by Wed, as
high pressure centers over eastern portions of the Great Basin and
a leeside trough forms over eastern WY. This will cause gusty
winds to form over the Wind Corridor Wed and Thu afternoon.
Conditions will remain dry through the period, with temperatures
on the seasonal to slightly below average side. 50+ degrees are
expected along the Cody Foothills, northern Johnson and Hot
Springs counties. These areas still have snow on the ground, so
will have to monitor for minor flooding that may occur. Temps will
reach 60 degrees in southern Johnson County, but there is no snow
on the ground there.

.LONG TERM...Thursday night through Monday

A weather system moves toward Western WY Thursday night and then
moves across WY on Friday. It is fast moving and this should limit
the snow totals in the western mountains to 6 inches or less in
most locations. Will keep an eye on it over the coming days. East
of the divide, rain or snow will be fairly light on Friday as the
system moves through the area. Weather pattern is more complex
Saturday through next Monday with a series of weather systems
impacting the region. The GFS and ECMWF models differ in the
details on timing of these systems. Saturday looks to have the
best chance of precipitation in the west and south with a lesser
chance in the north and central. Then a stronger system would
bring another round of precip to the west and south Sunday into
Sunday night. East of the divide, a chance of precip Sunday night
seems fine for now. Precipitation will linger into next Monday
morning and then decrease in the afternoon from west to east.
Temperatures will be near or above seasonal normals for mid



Patchy fog will be the main aviation concern in the valleys and
basin this morning, and again late Tuesday night. Boundary layer
moisture is on the dry side, so not expecting widespread fog. The
best chance Tuesday morning will be across the southwest in the
Kemmerer, Big Piney, and Rock Springs area. Otherwise, VFR
conditions with mainly SKC, and light winds today. A lee trough
developing Tuesday night will result in winds at KCPR picking up,
and some marginal low-level wind shear at KCOD after 06Z Wednesday.



Fire Danger low for all of WY through the next week, as a good
existing snow pack will combine with seasonal to below seasonal
temperatures and less wind to keep fire danger low for most of the
week. Smoke dispersion poor to briefly fair through Wednesday





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