Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 160416
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
116 PM MDT Sun Apr 15 2018

.SHORT TERM...(This evening through Wednesday)
Issued at 115 PM MDT Sun Apr 15 2018

In the west, Dry conditions are expected tonight and Monday with
strong gusty southwest winds developing Monday. Wind gusts of 45
to 55 mph are expected on the upper ridges and mountain passes.
A Pacific low pressure trough will bring moisture and instability
into the western mountains Monday night and Tuesday with snow
accumulations of 5 to 9 inches mainly above 8500 feet with rain
to a rain snow mix below 8500 feet. East of the Continental
Divide, Strong gusty wind and low relative humidity increase fire
danger on Monday. Southwest winds of 20 to 30 mph with gusts to
40 mph, combined with minimum relative humidity of 12 to 15
percent will produce conditions favorable for fires with rapid
rates of spread and erratic fire behavior from noon Monday to 7 pm
mdt Monday evening. Monday night and Tuesday the Pacific trough
will spread showers and a cold front across areas east of the
Continental divide with colder temperatures Tuesday night and
Wednesday.

.LONG TERM...(Wednesday night through Sunday)
Issued at 115 PM MDT Sun Apr 15 2018

The main concern in the long term continues to be the chance for
rain or snow arriving toward the end of the week. The models are in
decent agreement on the evolution of the storm, but as expected
there are some timing differences with the European keeping things
largely dry through Thursday and the GFS bringing in some
precipitation as early as later Wednesday night. The GFS is
notorious for rushing Pacific systems in too fast, especially in the
the medium and long range time frames. So as a result, we kept POPS
fairly low for Thursday with the main effects for Thursday night and
into Friday. There is not much change in the thinking for the
potential for some east to northwesterly upslope precipitation
during that time frame. Things are borderline for rain and snow,
especially for the daytime when we run into issues with the strong
mid April sun and even if it does snow it could have a tough time
sticking to paved surfaces. As a result only cosmetic changes we
made to the grids. The devil is always in the details and it is way
too soon for detailed QPF or potential snow accumulation numbers.

This system should move out later Friday night with more settled
weather for Saturday. The models then split on any shortwaves for
Saturday night or Sunday, and there will likely be some flip flops
this far out. So for now, we kept the weather mainly dry.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 115 PM MDT Sun Apr 15 2018

West of the Continental Divide...KJAC, KBPI, KPNA, and KRKS

Snow showers over the NW WY mountains will occur at times through
02Z Monday. KJAC airport will see rain or snow showers until 12Z
with MVFR conditions at times. Then VCSH will remain in the terminal
forecast through 02Z at KJAC with VFR conditions. VFR conditions are
then expected through most the rest of the period. The exception
will be in vicinity of KJAC but most of the heavier showers should
hold off until after 00Z Tuesday. A gusty to at times strong
southwest wind will develop after 17Z in vicinity of all TAF sites
except KJAC.

East of the Continental Divide...KCPR, KCOD, KRIW, KLND, and KWRL

VFR conditions are expected through the period. A gusty southwest
wind will develop at all TAF sites after 17Z Monday.

Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for
the latest information on icing and turbulence forecasts.

&&

.FIRE WEATHER...
Issued AT 115 PM MDT Sun Apr 15 2018

In the west, Dry conditions are expected tonight and Monday with
strong gusty southwest winds developing Monday. Wind gusts of 45
to 55 mph are expected on the upper ridges and mountain passes.
A Pacific low pressure trough will bring moisture and instability
into the western mountains Monday night and Tuesday with snow
accumulations of 5 to 9 inches mainly above 8500 feet with rain
to a rain snow mix below 8500 feet. East of the Continental
Divide, Strong gusty wind and low relative humidity increase fire
danger on Monday. Southwest winds of 20 to 30 mph with gusts to
40 mph, combined with minimum relative humidity of 12 to 15
percent will produce conditions favorable for fires with rapid
rates of spread and erratic fire behavior from noon Monday to 7 pm
mdt Monday evening. Monday night and Tuesday the Pacific trough
will spread showers and a cold front across areas east of the
Continental divide with colder temperatures Tuesday night and
Wednesday. Smoke dispersal will be very good or better on Monday
afternoon decreasing to fair to good on Tuesday as clouds lower
and showers become more widespread and temperatures fall with
an increasingly strong frontal inversion.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning from noon to 7 PM MDT Monday for WYZ280.

&&

$$

SHORT TERM...Baker
LONG TERM...Hattings
AVIATION...Hattings
FIRE WEATHER...Baker



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