Owl Creek Trail, Wyoming Weather Forecast Discussion

003
FXUS65 KRIW 181834
AFDRIW
Area Forecast Discussion
National Weather Service Riverton WY
1234 PM MDT Thu Sep 18 2025
.KEY MESSAGES...
- Warm and mostly dry conditions today through Saturday.
- A cold front treks across the area Sunday into Monday,
  bringing gusty winds, shower and thunderstorm chances, and
  cooler temperatures.
- Warm and dry weather returns Tuesday through much of next
  week.
&&
.UPDATE...
Issued at 1231 PM MDT Thu Sep 18 2025
18Z water vapor satellite imagery shows an upper trough over
the Plains and an upper ridge over the Great Basin. The forecast
remains on track for a pleasant day as the ridge builds over
the region. The upper trough`s associated upper low over Montana
is forecast to eject southeast late this evening into early
Friday morning. A weak shortwave disturbance will round the
backside of the low, and with enhanced PVA and some available
mid-level moisture, there will be support for very isolated
showers and thunderstorms (around 15% chance) across high
elevations of the northern Bighorns and far northeast Johnson
County between 9PM tonight and 2AM Friday.
A warmer day remains in store on Friday with mean 700mb temperatures
ranging from 7C to 10C. This reflects to high temperatures in the
mid to upper 70s to low 80s. However, increased cloud cover on
Friday, especially across southwest Wyoming, could keep temperatures
in the mid-70s range. These increased clouds will be associated with
an approaching weak upper level disturbance. This disturbance
may provide some support aloft for an isolated shower or
thunderstorm Friday afternoon and evening.
Otherwise, the forecast remains on track for the weekend with
elevated fire weather conditions Sunday afternoon ahead of a cold
front. With a slight uptick in moisture (mean RHs in the
20%-35% range) and gusty winds (20-30 mph) ahead of the front,
fire weather conditions remain marginal at this time. There
remains inconsistencies in the exact timing and coverage of
associated precipitation with the cold front. However, the most
likely timeframe is sometime between Sunday afternoon and Monday
morning.
&&
.DISCUSSION...
Issued at 123 AM MDT Thu Sep 18 2025
We are now entering a quieter period of weather as the upper
level low that brought the showers earlier this week has now
moved into the Plains states. Ridging will build over Wyoming
and bring a nice early autumn day for the most of the area,
with comfortably warm temperatures and light wind. The one small
fly in the ointment will be a weak shortwave dropping across
far eastern portions of our area. There may be just enough
instability and moisture for an isolated shower or thunderstorm
this evening in Johnson County. The chance is small with a
capital S though (less than 1 out of 6). Any threat of this
should end shortly after midnight.
Friday looks like a nice late summer day with temperatures averaging
around 10 degrees above normal. Saturday also looks like a nice day
across most of the area as well with warm temperatures and a few
more clouds. Some mid level moisture may try to approach
southwestern Wyoming and bring a late day or evening shower or
thunderstorm though. However, the chance once again is small
(less than 1 out of 5).
The next quandary in the forecast is what happens Sunday into Monday
with an approaching cold front. The latest model trend has moved
further south and a bit stronger with the front, and an upper level
low possibly developing as it passes through Wyoming. Coverage of
convection has increased with this latest model run as a
result. There has been a large lack of consistency with the
guidance with this system though, with models flip flopping more
than a fish out of water. My confidence in the passage with
some gusty wind and cooler temperatures for early next week is
high, but confidence of the details on placement or coverage of
any precipitation remains very low. Some more model consistency
could improve this though. With the frontal passage, there could
be some elevated fire weather ahead of it in the southwest
flow, pre-frontal areas Sunday, mainly Rock Springs to Casper.
Monday will be a cooler day in the wake of the front, with
temperatures near to a few degrees below normal.
Ridging should then build back northward for Tuesday and into
the middle of next week, bringing dry conditions and above
normal, but not hot temperatures, through Thursday.
&&
.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 1122 AM MDT Thu Sep 18 2025
VFR conditions will continue as ridging builds into the area. Wind
will be light through the period, with increasing high clouds
tonight through Friday morning.
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...Gerhardt
DISCUSSION...Hattings
AVIATION...Myers

NWS RIW Office Area Forecast Discussion