FXUS65 KRIW 211033

AFDRIW



Area Forecast Discussion

National Weather Service Riverton WY

433 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 /12Z TAFS THROUGH 12Z TUESDAY/...

Issued at 430 AM MDT Mon Sep 21 2026



VFR conditions expected for most locations to start the period.

Possible fog development for JAC/CPR to start the period that

will bring MVFR ceilings (~30%) through 15-16Z before lifting to

VFR for the remainder of the period. Otherwise, expect passing

high clouds and relatively light winds 10kts or less at allTAF

sites for the entirety of the period. Dry conditions with no

other weather elements expected at this time. 



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...Lowe