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000
FXUS65 KRIW 251908
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
108 PM MDT Thu Apr 25 2024

.KEY MESSAGES...

- More widely scattered rain showers and isolated thunderstorms
  this afternoon and evening.

- Main system pushes through Friday night and into the weekend
  with ample mountain snow and low valley rain.

- Warming trend and mainly dry next work week with another
  system late week and into the following weekend.

&&

.DISCUSSION...
Issued at 1236 PM MDT Thu Apr 25 2024

IR currently depicts the deep trough over the western CONUS with
cooling cloud tops through the CWA advecting in from the
southwest. Radar shows a much more sporadic day ahead with
widely scattered rain showers and some isolated thunderstorms.
This will continue through the afternoon and early evening hours
before subsiding with radiational cooling and the eventual FROPA
of a cool front. This is pushing into northwestern portions of
the state and will slowly move southeast throughout the
remainder of the day. Temperatures behind it are not much cooler
around 10 degrees from yesterday, but more seasonable in the
days ahead over the weekend.

With these rain showers and thunderstorms, there is enough
instability of DCAPE to see some gustier outflows for southern
counties and those east of the Divide from Wind River Basin to
the I-25 corridor. Updraft is not strong enough to see any type
of hail growth or potential for anything severe at this time.
The prone area with the best potential will be well east of the
CWA into far reaches of the state in eastern Wyoming and points
southeastward. Otherwise, a decent rain fall, even for the
higher terrain expected for the rest of today with the better
bullseye further east from Casper to Buffalo dependent on where
any showers/storms entrain upon one another.

This first initial shortwave off the main low coming in from
the Pacific northwest overnight into much of Friday. Initial
waves of snowfall to the higher terrain of the Absarokas and
Bighorns expected by mid afternoon spreading to the Winds by the
evening. Fairly slow moving over the weekend, substantial
snowfall expected with the Winds the highest amounts up to 1.5
to 2 feet with other ranges up to a foot possible. The better
dynamics and 700mb trough orientation looks to set up off the
Absarokas to the Winds with the highest probabilities over 18
inches of 80-90 percent. Over 12 inches with a 60-70 percent
probability elsewhere at this time. Regardless, winter
highlights have been issued to cover these ranges. Minor
accumulations with little to no impacts with the warmer
temperatures for lower areas west of the Divide.

Liquid precipitation is expected for the lower valleys east of
the Divide where the southern counties to be the possible
winners for the weekend. All areas need the moisture, but
especially this area. However, a minor flooding impact is
possible and something to keep an eye on where up to an inch is
possible. QPF amounts have come down as expected being a more
progressive than expected system. Less than half an inch for
other points to include the Wind River and Bighorn Basins, as
well as along the I-25 corridor. Confidence on the liquid
precipitation amounts are not as high as the snow, being more
of medium confidence at this time as models are not in great
agreement with one another.

Beyond the weekend, expect a warming trend and mainly dry
conditions for next work week as upper level ridging builds in
with increasing convergence aloft. Back to above average
temperatures and some windier days ahead for next week but
hopefully this overall system`s QPF amounts helps to alleviate
any fire weather concerns in the more long term. Beyond that,
long term models and outlooks show another GOA low pushing down
that could affect the CWA by next weekend hopefully to bring in
more of the much needed moisture.

&&

.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 1128 AM MDT Thu Apr 25 2024

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

Terminals to generally remain VFR through the forecast period.
Extensive cloud cover, with brief MVFR ceilings, over northwest
Wyoming late this morning should hinder destabilization around KJAC
this afternoon. As a result, have opted to avoid any TS mention at
KJAC. However to the south where sunshine has been prevalent this
morning, showers and a few thunderstorms were already erupting at
17Z/Thursday. This convection should move northeast through the
southwest terminals between 20Z-23Z. Brief MVFR is possible along
with erratic gusts 25-35kts. Mid-cloud decks remain overnight,
although there is a 30-50 percent chance of MVFR ceilings at KJAC
between 06Z-12Z/Friday. Mountain tops frequently obscured.

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

The first round of showers and isolated thunderstorms is lifting
into northern Wyoming late Thursday morning. Clearing behind this
wave will allow for destabilization and redevelopment of scattered
showers and isolated thunderstorms by mid-afternoon. Additional
convection over southwest Wyoming moves into the region late in the
afternoon. Have generally opted for short TS TEMPO groups between
about 22Z-02Z with erratic wind gusts 25-35kts the primary hazard.
Lingering light showers persist until 06Z/Friday. Mid-cloud decks
give way to lowering MVFR ceilings at KCOD around 10Z and eventually
KWRL at 14Z as northerly surface flow strengthens. Other terminals
to remain VFR through 12Z/Friday with possible localized MVFR after
14Z. Mountain tops frequently obscured after 10Z/Friday.

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

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from noon Friday to 3 PM MDT Saturday
for WYZ002.

Winter Weather Advisory from 3 PM Friday to 6 PM MDT Saturday
for WYZ008-009.

Winter Storm Warning from 6 PM Friday to 9 PM MDT Saturday for
WYZ015.

&&

$$

DISCUSSION...Lowe
AVIATION...Jones