FXUS65 KRIW 261707

AFDRIW



Area Forecast Discussion

National Weather Service Riverton WY

1107 AM MDT Thu Jun 26 2025



.KEY MESSAGES...



- Warmer and drier today with only isolated thunderstorms in

  northern Wyoming. Elevated fire weather is likely in central

  and southern Wyoming.



- Elevated to critical fire weather is likely for much of the 

  area on Friday afternoon. 



- Above normal temperatures are expected to continue through the

  weekend into early next week.



&&



.DISCUSSION...

Issued at 249 AM MDT Thu Jun 26 2025



June is typically the most active month for severe weather 

(hail, tornadoes) etc in western and central Wyoming and the 

past month is no exception. Eventually, we begin to transition 

into a drier time when fire weather concerns become the main 

concern and while we are not completely there yet, we have 

begun the slow transition. 



Flat ridging will dominate the weather through around Saturday. This 

typically means flow will be mainly from the west and southwest, and 

will bring warmer temperatures. We will see a period of above normal 

temperature through the weekend. Areas in our warmer locations, like 

Greybull and Worland, will see highs climb back close to the 90s 

today with 80s widespread across most of the lower elevations. We 

could still see a few thunderstorms today, mainly across the 

northern mountains and adjacent foothills as a shortwave brushes by 

to the north. The atmosphere is much drier today though. This is the 

first day in a while that precipitable water values are below 

the 50th percentile. This means coverage will be isolated (at 

most a 1 out of 5 chance). However, it also means dewpoint 

depressions will be large so any thunderstorm or shower that 

forms could have strong wind gusts of 40-50 mph. As for fire 

weather concerns, humidity will be low, falling below 15 percent

in many lower elevation locations (especially across central and

southern portions). Wind should remain on the light to moderate

side, so critical fire weather is not expected.



Concerns do increase on Friday though. Another shortwave will move 

by to the north. Again, isolated storms (a 1 out of 6 chance) 

will be possible in the northwest but this is the main concern.

The pressure gradient will be a bit tighter. In addition, a jet

streak moving across Montana will put Wyoming in the right 

front quadrant of the jet, enhancing downward momentum of 20 to 

30 knot 700 millibar winds. Increased southwest flow will also 

bring a hot day, with fairly widespread highs in the low to mid 

90s. Humidity will be very low as well, falling into the single

digits at this time. Additionally, fuels have turned critical 

in a few locations. One of these locations is Natrona County, 

and this is also one of our windier locations. With this, we 

have hoisted a Fire Weather Watch for Friday afternoon and 

evening. Other locations could have elevated to critical fire 

weather, but less wind or fuels not being critical should 

prevent more widespread watches.



On Saturday, we have a few more questions. We thought about going 

two days on the Watch, but have held off for now. For one, the 

best jet forcing moves a bit further north, reducing downward 

momentum. The result is wind should be a bit lighter. In 

addition, most guidance shows a bit more moisture moving in, 

raising dewpoints anywhere from 5 to 10 degrees, making things 

more borderline. The increased moisture and with what forcing we

have from the right rear quadrant of the jet, thunderstorm 

chances may increase a bit, but the chance is still only around 

1 out of 4. 



A somewhat stronger wave and associated weak cold front will swing 

through the area on Sunday, taking the edge off of the heat. It will 

also increase chances for showers and storms in eastern portions of 

the area, where surface easterly flow may provide convective 

initiation, mainly in Johnson and Natrona Counties. Ridging then

builds northward for early next week, resulting in above normal

temperatures again. Most convection these days should be in the

mountains and adjacent foothills, but any spot generally only 

has a 1 in 4 chance of a shower or thunderstorm. Another wave 

may bring increased showers and storms for Wednesday, but timing

this far out is uncertain.



&&



.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...

Issued at 1105 AM MDT Thu Jun 26 2025



VFR flight conditions prevail the entire TAF period at all terminals 

with afternoon CU development and increasing mid-level clouds. 

Westerly winds increase between 19-22Z at all west of the Divide 

terminals and KCPR with gusts around 20kts. Gusty winds diminish 

around sunset. Winds less than 10kts are forecast at all other 

terminals.



Isolated showers and thunderstorms are possible across western and 

northern Wyoming between 21Z-04Z. Confidence is highest (30%) in a 

shower and/or thunderstorm at KCOD and this is reflected as a PROB30 

group. Confidence is too low (20%) in a shower and/or thunderstorm 

at KJAC and KWRL so there is no mention is TAF at this time. A 

thunderstorm could produce gusty outflows around 30kts. 



Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for 

the latest information on smoke, icing, and turbulence

forecasts.



&&



.FIRE WEATHER...

Issued at 249 AM MDT Thu Jun 26 2025



Elevated fire weather is possible this afternoon with humidity

falling below 15 percent across much of the southern half of the

area. Wind should remain light to moderate though. On Friday,

stronger wind, combined with low humidity, will lead to the

likelihood of elevated to critical fire weather across much of

the area. A Fire Weather Watch has been issued for zone 280 as a

result.



&&



.RIW WATCHES/WARNINGS/ADVISORIES...

Fire Weather Watch from Friday afternoon through Friday 

evening for WYZ280.



&&



$$



DISCUSSION...Hattings

AVIATION...Gerhardt

FIRE WEATHER...

