FXUS65 KRIW 092204

AFDRIW



Area Forecast Discussion

National Weather Service Riverton WY

404 PM MDT Fri May 9 2025



.KEY MESSAGES...



- Isolated showers and thunderstorms continue through the

  afternoon, especially in Johnson and Natrona counties.



- A warm weekend is in store as temperatures peak into the 70s

  and 80s across the lower elevations. This may lead to 

  elevated river and stream levels early next week as snowmelt 

  increases.



- Sunday will see increased shower and thunderstorm chances, 

  especially across western Wyoming.



- Gusty winds, warm temperatures, and low humidity will bring elevated

  to critical fire weather conditions Sunday and Monday for 

  much of the area.



- The next system approaches on Tuesday. Confidence is beginning

  to increase for this system to bring widespread rain and

  mountain snow through midweek, especially across northern and

  western Wyoming.



&&



.UPDATE...

Issued at 142 PM MDT Fri May 9 2025



Isolated convection will continue today, focused mainly on the 

eastern half of the area off of the higher terrain. This activity 

will drift to the southeast through the afternoon, ending around 

sunset. Gusty outflow winds to 35 mph or so will be the main 

concern. 



No big changes this afternoon to the upcoming forecast. The weekend 

will see temperatures warm to near 20 degrees above normal for most 

of the area. The ridge will begin to move east on Sunday, allowing 

for the return of more widespread convection chances, especially 

west of the Divide. 



There are a couple of resultant weather concerns we are beginning to 

key in on. One is the potential for rising rivers and streams given 

the multiple days of above normal temperatures expected this 

weekend. The other is fire weather conditions as southwesterly winds 

increase ahead of next week's system. This will first be a concern 

on Sunday, though Monday will be the day with the strongest wind and 

lowest humidity.



&&



.DISCUSSION...

Issued at 211 AM MDT Fri May 9 2025



The H5 ridge continues to build, and will stretch northward

along the Rockies today. The ridge will continue to bring

temperatures will above normal in the 70s and low 80s this

afternoon. The weak shortwave that's drifting along the 

northern edge of the ridge will mosey across the Bighorn Range 

this afternoon, and will tap enough instability from heating of 

the day to spark a few showers and thunderstorms. Steer flow is

toward the southeast, so areas of Johnson and Natrona Counties 

also have a 20 to 30 percent chance for thunderstorms as well. 

As was that case assisted, once peak heating wanes and the 

ridge continues building northward, shower activity will fade 

away early in the evening.



The weekend will be marked by even warmer conditions as the axis

of the ridge centers on Wyoming. H7 temps still lead to highs 

in the mid to upper 70s west of the divide and low to mid 80s 

east of the divide. Early next week, the ridge gets pushed east

by a longwave trough off the PacNW coast. Western WY remains 

pinned between the two, but the H7 heat ridge holds across the 

state Monday and Tuesday. Temps will be a few degrees cooler 

these days, held down by the increasing cloud cover from the 

approaching trough. Models still having trouble resolving the 

progress of the trough, with GFS running faster, and EC holding 

back a bit, but feeding more Pacific moisture into the state. 

With either solution, there is an increasing potential for an 

extended period of rain/snow for western WY into midweek.



&&



.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...

Issued at 404 PM MDT Fri May 9 2025



High pressure will keep VFR conditions at terminals through the 

period. The ongoing, isolated convection across the eastern half of 

the area will linger through the afternoon. The best chance for 

brief terminal impacts will be at KCPR but this will be short-lived, 

with any showers or storms ending around sunset. Wind will generally 

be light through the period, though outflow from any showers in the 

broader area may lead to briefly increased wind gusts through the 

evening. No precipitation is expected to impact terminals on 

Saturday.



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...

None.



&&



$$



UPDATE...Myers

DISCUSSION...Straub

AVIATION...Myers