Odonnell Spur, Wyoming Weather Forecast Discussion

706
FXUS65 KRIW 282004
AFDRIW
Area Forecast Discussion
National Weather Service Riverton WY
204 PM MDT Sun Sep 28 2025
.KEY MESSAGES...
- Widely scattered (20-30%) showers and thunderstorms across
  western portions this afternoon and evening.
- Chances are low (10-20%) for locally heavy rain with the
  stronger storms this afternoon.
- Shower and thunderstorms will be possible over western
  portions again on Tuesday.
&&
.UPDATE...
Issued at 150 PM MDT Sun Sep 28 2025
Open wave continues to sweep northward and weaken. There is
still enough energy and moisture to spark showers and
thunderstorms along the higher terrain, but this is having
trouble moving off the terrain. With available moisture still
above normal, some showers could produce a quick tenth to two-
tenths of rainfall as they pass. Showers will be ending quickly
this evening with loss of daytime heating, with mostly clear
skies expected. The open trough axis will be to the northeast
most of Tuesday, so shower activity will be more isolated in
nature and still restricted to higher elevations.
&&
.DISCUSSION...
Issued at 125 AM MDT Sun Sep 28 2025
Not much change in the forecast. 05Z satellite imagery shows clouds
beginning to increase from the south over Sweetwater and Lincoln
counties and the Upper Green River Basin. Weak virga showers are
also showing up on radar in these areas. Moisture/clouds will
continue to stream northward this morning and through the day today,
leading to widely scattered (20-30%) showers and thunderstorms to
occur over mainly western portions of the CWA through the afternoon.
Some of these showers/storms will spill over near Dubois, Meeteetse
and Cody, as the come off the east slopes of the Wind River and
Absaroka Mountains. Wind gusts of 40 to 50 mph will be the main
threat, as T/Td spreads will be around 40 degrees. Locally heavy
rain cannot be ruled out from the stronger storms either, as PWATs
of 0.6" to 0.8" will be in place by late this afternoon. This,
coupled with generally weak steering flow, could lead to brief heavy
downpours. Any remaining shower or storm is expected to end by
midnight (06Z), with isolated weak showers remaining possible
over the central basins through 09Z. Otherwise, temperatures
will continue to be above normal for areas east of the Divide
and near normal west of the Divide.
A cutoff low, that has been nearly stationary over the Desert
Southwest the last few days, will begin to fill today and get kicked
from a significant longwave trough over the EPAC. This trough will
be the focus for the next week. Showers and isolated thunderstorms
will be possible over the western mountains again, including areas
near Dubois and Cody. Otherwise, conditions will be somewhat similar
to today.
The longwave trough will move onshore over the West Coast Monday
night into Tuesday, filling and weakening as it does so. Showers and
thunderstorms will be possible over western portions Tuesday
afternoon as a result. A southwest flow pattern will Wednesday
through Friday, as a closed low associated with the longwave trough
will make little progression eastward due to a strong high center
over the mid-Mississippi River Valley. No embedded shortwave troughs
are expected to move over the Cowboy State Wednesday and Thursday,
keeping conditions dry. Elevated fire weather conditions do not look
as likely Thursday, as 700mb winds have decreased to 20-30 kt. Model
consensus begins to diverge by Friday due to this high center
(coincidentally, this will also likely affect the forecast for
Tropical Depression 9), with the ECMWF weakening both the high and
PACNW low and bringing widespread precipitation chances across the
CWA as the trough moves over the region. Strangely, the GFS is the
slower solution and keeps the low closed as it digs southward over
northern CA/NV. This would keep precipitation chances to western
portions of the state Friday afternoon into Saturday morning.
&&
.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1100 AM MDT Sun Sep 28 2025
VFR conditions are expected to prevail throughout much of the
TAF period. However, as a disturbance nears the area lowering
cloud decks with showers and thunderstorms may lead to brief
periods of MVFR/IFR conditions. The best chances for showers and
thunderstorms look to be at KJAC, KCOD, KBPI, and KPNA starting
shortly after that start of the period. Short range convective
models still show a chance for an isolated shower or
thunderstorm over the Wind River Basin. As a result PROB30
groups for thunderstorm showers remain at KLND and KRIW from 21Z
to 03Z Monday. KCPR may see an isolated shower this evening but
confidence is low at this time. Clouds are expected to decrease
overnight with some mid level clouds linger into the end of the
TAF period on Monday. Winds will see a slight increase this
afternoon with speeds around 10 to 15 knots at times. Stronger
wind gusts of 20 to 30 knots may be possible nearby any
developing showers and thunderstorms. Winds decrease by the late
evening into the early morning hours Monday with light winds
remaining through the end of the TAF period.
Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for
the latest information on smoke, icing, and turbulence
forecasts.
&&
.RIW WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
UPDATE...Straub
DISCUSSION...LaVoie
AVIATION...Dziewaltowski

NWS RIW Office Area Forecast Discussion