textproduct: Western and Central Wyoming

KEY MESSAGES

- Still warm but not quite as hot today with less wind than yesterday.

- Record heat is likely on Wednesday afternoon. An approaching weather system will bring strong winds as well as some showers and thunderstorms, with very strong wind gusts possible with any shower or storm.

- Warm temperatures, low humidity and gusty wind will bring elevated to near critical fire weather each afternoon from Wednesday through Friday.

DISCUSSION

Issued at 215 AM MDT Tue May 12 2026

Recently I was discussing underrated films of the past, most specifically in the 90s. And one of the movies that was brought up will be the story across the area over the next couple of days, but especially on Wednesday. If you guessed the 1995 police / crime action / drama "Heat", you would be correct.

We had several record high temperatures set across western Wyoming on Monday afternoon. Expect another day of well above normal high temperatures today. However, with the passage a cold front (if you can call it that, more like a not quite as hot front.) Temperatures will be down around 5 to 10 degrees compared to yesterday East of the Divide. However, West of the Divide it will be another very warm day with most lower elevations well into the 80s, leading to another very warm day, possibly with more record highs. As for any showers, we can't rule out a stray shower near the mountains, but with the chance less than 1 out of 7 we left the forecast dry for now. Also, with the ridge axis building over the area, wind should be lighter than today, leading to some decrease of fire weather concerns.

Wednesday looks to be the warmest day, and more active in regards to impacts. There are three main concerns. We will start with the heat. On this day, 700 millibar temperatures climbing as high as 15 celsius. This is combined with increased southwest wind head of an advancing cold front. This will lead to downsloping flow leading to compression warming to bring the warmest day East of the Divide. Locations in Big Horn Basin from Thermopolis through Lovell have a greater than 3 out of 4 chance of seeing their first 90 degree high temperatures of the year, with a 1 in 4 chance of temperatures as high as 95. As for earliest 90 degree high temperatures, these locations have already passed these dates. Places like Riverton, Lander and Casper have around a 2 in 5 chance of seeing a high temperatures of 90 as well. And here it would be the earliest 90 degree high temperatures in history (currents are May 14th in downtown Riverton, May 20th in Lander, May 26th in Casper and May 28th at the Riverton airport). Numerous high temperatures records are expected to fall regardless.

The second concern is fire weather. All fuels in western and central Wyoming have been deemed not critical, so no Red Flag Warnings will be issued. However, with a greater than 4 out of 5 chance of relative humidity falling below 15 percent across most of the eastern two thirds of the area and a greater than 3 out of 4 chance of wind gusts of 25 mph or greater in the afternoon, elevated to near critical fire weather is a near certainty. Burning is not advised on Wednesday, especially in the afternoon.

And finally, we turn to convection. The cold front will approach the western portions of the state in the afternoon, in association with an 80 knot jet streak to provide some upper level forcing. Instability parameters look good as well with as much as 700 J/Kg of CAPE and lifted indices as low as minus 3. The one thing missing is low level moisture, although there is a decent amount of mid level moisture. This looks like a very good set up for downburst winds. We have very steep lapse rates of greater than 9 degrees celsius per kilometer. Sounding have a well defined inverted V signature with LCL levels anywhere from 6000 to 9000 feet off the surface. And guidance gives very large dew point depressions approaching 60 degrees fahrenheit. The Storm Prediction Center has noted this as well and has hoisted a marginal risk across far western Wyoming. This looks like an ideal "Little Green Blob" day as well with any shower or even a cumulus cloud possibly producing wind gusts over 50 mph. Most convection looks diurnal, ending by midnight.

Thursday and Friday look similar with flat ridging across Wyoming. Temperatures will continue to be above normal, but not record breaking, averaging 10 to 15 degrees above normal. Fire weather will continue to be a concern as relative humidity remains very low and wind remains rather gusty. And there is the chance of high winds on Thursday. This is mainly in the Cody Foothills with a shortwave moving across Montana along with an associated jet streak. Model guidance also shows 50 to 55 knots of westerly wind at 700 millibars. There is a greater than 1 out of 2 chance of wind gusts 55 mph or greater. However, right now this is mainly in locations near the Absarokas where there is little impact. We still have time to decide on any potential highlights though. Gusty wind continues on Friday but with the jet moving away the threat of high wind should end. With low humidity continuing as well, elevated fire weather will continue through Friday.

We could see a bit of a pattern change on Saturday and especially Sunday as a trough and cold front digs into the northern Rockies. This is especially so on Sunday as some model guidance shows 700 millibar temperatures falling as low as minus 6. If any moisture can work in this likely means mountain snow and possibly even in some of the lower elevations. There is poor agreement on any placement of potential precipitation though. However, there is a decent chance of a cooler pattern arriving this weekend and possibly lasting into early next week.

AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/

Issued at 1105 AM MDT Tue May 12 2026

VFR conditions prevail through the period. Fairly light winds today, with gusts to around 20 knots at KBPI, KPNA, and KRKS this afternoon. Otherwise, a mainly clear sky across the area. A few virga showers are possible around KRKS between 22z and 01z, which could locally bring some gusty winds; have added a VCSH group to account for these.

Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for the latest information on icing and turbulence forecasts.

FIRE WEATHER

Issued at 215 AM MDT Tue May 12 2026

Although relative humidity will remain under 15 percent in some locations today, somewhat cooler temperatures and less wind should ease fire concerns somewhat. On Wednesday, a combination of record warm temperatures, a gusty to strong southwest wind and humidity under 15 percent will bring elevated to near critical fire weather to much of the area. Dry showers and thunderstorms are also possible in the afternoon, especially across western Wyoming with wind gusts past 50 mph possible with any shower or thunderstorm. Although temperatures will cool somewhat Thursday and Friday, a continued gusty to strong wind and low humidity will keep elevated fire weather in place across much of the area.

RIW WATCHES/WARNINGS/ADVISORIES

None.