FXUS65 KRIW 210730

AFDRIW



Area Forecast Discussion

National Weather Service Riverton WY

130 AM MDT Mon Sep 21 2026



.KEY MESSAGES...



- Temperatures will be a bit chilly come Monday morning, with

  lows in the 30s and middle 40s with closer to seasonable 

  temperatures in the afternoon.

 

- Areas of fog are possible Monday morning across much of central

  and western Wyoming, especially in low-lying areas.



- Apart from shower and thunderstorm chances (40% to 70%) on

  Tuesday afternoon and evening, this work week is forecast to

  be dry with above average temperatures returning by Thursday.



&&



.DISCUSSION...

Issued at 130 AM MDT Mon Sep 21 2026



Diminishing cloud cover across the CWA in wake of the weekend's

storm system that brought much needed and ample precipitation,

especially east of the Divide. IR shows warming cloud tops as

the aforementioned system makes its way eastward across the

upper Great Plains to the Great Lakes stretching southward all

the way to the Gulf of America. WV shows the main finger of the

PFJ well to the north across Canada pushing cyclonically around

an upper level low over the Gulf of Alaska. Another weak low

near California will be the next system to bring in storm

activity for Tuesday afternoon and evening with its slow

progression east and northeastward. 



With the clear skies west of the Divide, expect fog development

over some of the area. Jackson hole looks to be the best chance

for a heavier impact with the surrounding lakes and recent

rainfall. Points further east of the Divide, the cloud cover

looks to hinder much of the area but possible (10-20%) around

the Casper area but confidence low at this point in time

dependent on cloud cover by Monday morning sunrise. Beyond that,

expect light winds and seasonable temperatures into the

afternoon with tranquil weather conditions to be had heading

into the next system for later Tuesday. 



The aforementioned closed low near California will become more 

of an open and progressive wave with its northeastward movement 

through the upper Rockies Tuesday afternoon and evening. 

Scattered rain showers and isolated thunderstorms likely 

(40-70%) for much of the area west of the Divide, with lower 

confidence to the east (20-40%). The strongest PVA anomalies 

look to occur across Sweetwater County through the upper Green 

River Basin for the strongest storms to occur. The likely 

impacts will be that of heavy rainfall and gusty outflow winds.

Hi-res models are pushing the 36 hour limit on its output but 

it tends to be close enough at this point in time. The Winds 

will likely block much impact to the east, but strong winds will

be the main factor pushing down into the Wind River Basin 

towards sunset Tuesday evening. 



Beyond Tuesday's storm and shower activity, expect induce

ridging to build in through the Rockies that will bring above

average temperatures for the remainder of the work week. Winds

will be relatively tame for the week as well with no indications

of fire weather concerns at this point in time. The next system

looks to push in by Friday night into the weekend as the

aforementioned GOA low extends down into the Pacific Northwest 

as the PFJ dips into the continental US. Early indications of 

model runs keep the main impacts north into Montana but still 

affects to be had in the CWA with precipitation and more 

seasonable temperatures for the weekend and into the following 

week. 



&&



.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...

Issued at 1030 PM MDT Sun Sep 20 2026



VFR conditions to start the period across all terminals with 

precipitation moving out of the area. The main concern tonight into 

Monday morning will be the potential for areas of fog to develop. 

Due to lingering cloud cover confidence at this time remains low 

with high uncertainty regarding exact locations, timing, and any 

terminals impacts. KCPR and KJAC look to have the best chances for 

seeing some fog develop and as a result TEMPOs are in place from 11Z 

to 16Z. The remaining terminals at this time look less likely to see 

impacts from any potential fog. Fair weather clouds and light winds 

less then 10 knots are expected to prevail through the afternoon and 

evening Monday. VFR conditions persist to end the TAF period with 

clouds starting to increase in association with the next 

disturbance.  



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.



&&



$$



DISCUSSION...Lowe

AVIATION...Dziewaltowski