Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 200607
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1107 PM MST Sun Feb 19 2017

.Short Term...Tonight Through Wednesday (Issued at 248 PM MST)

There will be a break in the heavier snow in the west tonight
through Monday.  Strong west to southwest winds will bring
periods of high winds to the Cody foothills. A high wind warning
has been issued.  As the strong winds aloft shift further south,
high winds will be possible across Fremont and Natrona county.
Pacific moisture will increase significantly bringing a long
duration heavy snow event to the western mountains.  A strong
Pacific storm will bring heavy snow to the western mountains from
Monday afternoon through Tuesday evening. Strong west to
southwest winds will cause blowing and drifting snow. The western
valleys will see mainly rain. Snowfall of 12 to 24 inches is
expected, possibly up to 30 inches in the Teton mountains. West to
southwest winds of 25 to 30 mph with gusts of 45 to 50 mph on the
passes and upper ridges. Visibility frequently below a quarter
mile in heavy snow and blowing snow. Some rain and rain snow mix
may spill over the mountains to areas east of the continental
divide but this should be light and very spotty.

.Long Term...Wednesday Night Through Sunday

The main concern in the long range continues to be the potential
snow storm in the Wednesday night and Thursday timeframe. One change
is the models have trended a little bit slower in the onset of the
precipitation across areas East of the Divide. As a result, we
lowered POPS a bit in that area. Future shifts may want to lower
them further if this trend continues. The exception may be across
the Interstate 80 corridor which will be in the more favorable left
front quadrant of the jet.

The models have come into somewhat better agreement with the
evolution of the snowstorm, although the exact details remain in
question, as would be expected this far out from the storm. It still
appears that the biggest impact would be further east, especially in
the favored northeasterly upslope flow, especially in Natrona
County. However, the latest runs of both the GFS and European have
shifted the the best lift and QPF a bit further to the east and into
eastern Wyoming. The GFS especially so and has a place like Riverton
with only light snow. It is too early to bite too hard on these
solutions though since it is still a few days out though. For now,
we maintained the likely POPS over the favored upslope areas but
lowered them a bit elsewhere. Thursday will be a shock to the system
after the recent run of mild weather with chilly temperatures with
possible falling temperatures all day. Nothing unusual for February
however. The heaviest snow will move out after Thursday evening.

Friday looks like a cloudy and chilly day at this point. Another
wave will move through the area with another chance of snow.
However, this one is weaker and has much less moisture to work with
so mainly light snow is anticipated with it. As for next weekend, we
made few changes with many slight to chance POPS across the west
with a couple of waves moving down and mainly dry conditions
persisting East of the Divide. Temperatures will be below normal,
but not extremely cold and certainly nothing unusual for the end of
February.

&&

.Aviation.../06Z Issuance/

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

A few snow showers in the western mountains overnight. Snow will
be developing over the western mountains Monday morning and snow
will continue through Monday night. MVFR/IFR conditions will occur
in and near the mountains. KJAC airport will see snow starting
around 15Z and snow is expected through Monday night with MVFR to
IFR conditions. KPNA and KBPI airports will see VCSH by 19Z with
snow developing at these sites between 00Z and 05Z Tuesday.
KRKS airport will have VFR conditions through the period.

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

VFR conditions will prevail at the terminal sites through the
period. A gusty wind will occur at KCPR airport after 15Z and
this gusty wind will continue through Monday night.

&&

.Fire Weather...

There will be a break in the heavier snow in the west tonight
through Monday.  Strong west to southwest winds will bring
periods of high winds to the Cody foothills. A high wind warning
has been issued.  As the strong winds aloft shift further south,
high winds will be possible across Fremont and Natrona county.
Pacific moisture will increase significantly bringing a long
duration heavy snow event to the western mountains.  A strong
Pacific storm will bring heavy snow to the western mountains from
Monday afternoon through Tuesday evening. Strong west to
southwest winds will cause blowing and drifting snow. The western
valleys will see mainly rain. Snowfall of 12 to 24 inches is
expected, possibly up to 30 inches in the Teton mountains. West to
southwest winds of 25 to 30 mph with gusts of 45 to 50 mph on the
passes and upper ridges. Visibility frequently below a quarter
mile in heavy snow and blowing snow. Some rain and rain snow mix
may spill over the mountains to areas east of the continental
divide but this should be light and very spotty.   The areas with
precipitation in the west will have poor smoke dispersal through
Wednesday, while the winder areas east of the mountains will see
fair to good smoke dispersal in the afternoons. The Bighorn basin
and Wind River basin will have less wind and poor smoke dispersal.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...

Winter Storm Watch from Monday afternoon through Tuesday evening
for WYZ001-002-012-014-024.

High Wind Watch from late tonight through Tuesday morning for
WYZ015-018>020.

High Wind Warning from 6 PM this evening to 5 PM MST Monday for
WYZ003.

&&

$$

SHORT TERM...C.Baker
LONG TERM...CH
AVIATION...AR
FIRE WEATHER...C.Baker



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