Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 121000
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
400 AM MDT Mon Apr 12 2021

.SHORT TERM...(Today through Tuesday)
Issued at 400 AM MDT Mon Apr 12 2021

Light snow has increased in the Wind River Basin and east slopes
of the Wind River mountains since 05Z. Light snow is occurring in
Natrona county as well. Accumulations are light, except for Lander
and the east slopes. Will get some reports in the morning which
could be interesting. Roads are wet for the most part. This snow
is a combination of low level upslope and a weather system aloft
moving through the northwest flow. The snow will gradually end
after sunrise as the weather system departs and the moisture
decreases. Snow showers will still occur in most mountains through
the afternoon, ending this evening. Accumulations will be light.
The north, far west, and south will be dry today and tonight. High
temperatures will be on the cold side again today with 30s and
40s, 20s for most mountains. Lows tonight will be in the 20s with
some upper teens in places. Expect single digits and teens for
lows in the mountains.

Tuesday will be dry for most places. There may be some light snow
developing in the south late Tuesday afternoon ahead of a weather
disturbance that moves toward that area Tuesday night. High temps
will remain below normal with 30s and 40s, and mainly 20s in the
mountains. It will be windy across the south Tuesday with a
northeast wind gusting over 40 mph in Sweetwater county, southern
Sublette county, and southern Lincoln county. Breezy areas elsewhere.


.LONG TERM...(Tuesday night through Monday)
Issued at 400 AM MDT Mon Apr 12 2021

The much below normal temperatures and the projected snowfall that
have been previously advertised are the main stories for the long-
term.  The challenge to these is going to be snow amounts during the
daylight hours and on the roads due to the high sun angle as it is
now almost the middle of April.  Now to move into more of the
details.

The beginning of the period (00Z Wednesday) shows the cut-off low in
the area of the CA/OR/NV border area.  The GFS shows the most
precipitation of the four main models and keeps it primarily over UT
and CO, with a bit pushing into far southwestern WY.  The other
models are drier, but keep the moisture as well mainly south of the
CWA.  Moving throughout the day, the precipitation coverage looks to
increase as the area of moisture pinwheels around the low from the
southwest.  By 00Z Thursday, the low is forecasted to be just a bit
further east. The general pattern from Wednesday looks to continue
into Thursday.  Models start to diverge more into Friday as the cut-
off becomes part of the main flow and is projected to start moving
more to the east.  As of this point it looks like most of the
moisture may be confined to the easternmost parts of the CWA on
Friday.  Temperatures at H7 look to be between -6 to -12 during
Wednesday and Thursday so all precipitation should be in the form of
snow.  The only exception may be in southern portion of Sweetwater
County, where a pocket of a bit warmer air may push into the area.
Projected snow totals at this time look to be around 4-5" for parts
of the Wind River Basin; 7-8" for KLND; up to a foot possible in the
Wind River Range; up to 6" in the Bighorns, around 5-6" in the
Tetons and around 2" for Sweetwater County.  Since it is a fairly
long duration event, however and due to it being mid-April, much of
the snow may only accumulate on grassy areas and not be a factor on
roads during the daylight hours.  Temperatures should stay mainly in
the 30s for both Wednesday and Thursday with the snow and abundant
cloud cover.

For Friday, as the system looks to start moving out of the area,
some precipitation is still expected, but temperatures may improve
by a couple of degrees over Thursday, but still may struggle to
reach much above 40 in many spots.  This would be especially true if
there is a blanket of snow.  Into Saturday, models continue to
differ.  The GFS keeps moisture over the area with an east-west
oriented trough draped near the southern border of the state.  The
EC/CMC have it dry.  All show a good northerly to northeasterly wind
so temperatures look to still remain below normal. Temperatures
finally look to rebound to back to near normal by Sunday.  Models
pick up on another area of moisture moving in from the north during
the day Monday, but confidence is low at this point.

&&

.AVIATION...(For the 12Z TAFS through 12Z Tuesday)
Issued at 400 AM MDT Mon Apr 12 2021

East of the Divide...KCOD/KCPR/KLND/KRIW/KWRL Terminals

Some snow showers will be ongoing to start the TAF period,
especially near KLND, KRIW, and KCPR. However improving conditions
are expected this morning from north to south. KLND looks to keep
MVFR conditions the longest into late this morning. VFR conditions
are expected at area terminals this afternoon into this evening,
but there will continue to be mountain snow showers as well as
some obscurations before all showers and after sunset this
evening. Largely VFR conditions are expected tonight.

West of the Divide...KBPI/KJAC/KPNA/KRKS Terminals

VFR conditions are expected at all terminals through the period.
Winds will generally be light through the period, except for the
south, including KRKS, where breezy northeast to east winds will
continue. These winds at KRKS will then last through the TAF period.
During the afternoon, there looks to be increasing cloudiness as
some snow showers possibly push west over the Continental Divide.
The most likely location would be in vicinity of KPNA but not
enough confidence for anything but VCSH yet.

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 400 AM MDT Mon Apr 12 2021

Areas of light snow will be ending in the central zones by late
morning. Snow showers will occur in most mountains zones today,
ending this evening. Otherwise, dry weather over the region with
cool temperatures. Breezy areas today in the north and far south.
Smoke dispersal will be good to very good in the afternoon. Mainly
dry tonight and Tuesday over the region. Some light snow may move
into Sweetwater county late Tuesday afternoon. Breezy areas, with
windy conditions in the south zones as a northeast to east wind
occurs there. Still cool on Tuesday with below normal temperatures.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$

SHORT TERM...AR
LONG TERM...Clayton
AVIATION...Hattings
FIRE WEATHER...AR


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