textproduct: Cheyenne

KEY MESSAGES

- Near record high temperatures are expected to begin today and continue through Monday.

- Widely scattered high-based showers and thunderstorms with potential for strong gusty winds are expected today and tomorrow.

- Another surge of monsoon moisture will arrive Monday, increasing rainfall chances for the early part of the work week.

SHORT TERM /THROUGH MONDAY NIGHT/

Issued at 400 AM MDT Sat Jul 25 2026

Hot temperatures will be the primary near term concern. The powerful upper level ridge over the Four Corners states continues to amplify this morning, setting the stage for near record heat today and tomorrow. 700-mb temperatures analyzed this morning appear to range from about +16 to +18C across the area, but this is expected to warm by a few degrees Celsius over the day, peaking between +18C and +20C late this afternoon. The heat wave will peak on Sunday, with NAEFS mean 700-mb temperatures near or over +20C for much of the area. Friday's highs ended up several degrees warmer than forecast, and the heat aloft strengthens further today. The 5000 ft elevation contour will provide a pretty good estimate of where to expect temperatures over 100 degrees today. Look for 100s at elevations below about 5000 ft, and 90s at higher elevations. The lowest elevation locations around the Chadron area will see highs over 105 and possibly even approaching 110 degrees (20% chance). Sunday's highs will be similar if not a degree or two higher than today. In addition to the hot daytime temperatures, we will really struggle to cool down overnight over the next few days, especially tonight. A modest low-level jet in the Nebraska panhandle may keep downslope southerly winds off the Pine Ridge all through the night, keeping temperatures in the upper 70s or higher all night. Because of this, northern Sioux and Dawes counties were both upgraded to an Extreme Heat Warning for daytime high temperatures between 105 and 110, and overnight lows between 75 and 80 degrees. Heat Advisories remain in effect for remaining areas of the High Plains through Monday. Monday should be a few degrees cooler than Sunday, and thus more marginal for heat headlines. It is possible the heat headlines could be expired early as the latest forecast keeps Monday's highs in the 95 to 98 percentile range rather than 99+ as it is for Saturday and Sunday.

One uncertainty with the high temperatures both today and tomorrow will be increased potential for convective activity. GOES satellite imagery this morning shows a subtle upper level shortwave rotating over the top of the powerful ridge. Higher middle to upper atmosphere moisture content is apparent with this feature on water vapor channels. Vorticity associated with this feature will move across the area this afternoon and evening, providing lift in the place of modest high-based instability. High- resolution models have trended more aggressive with coverage of this activity this afternoon. The NBM continues to be far too low, so PoPs were increased midday through midnight today. The highest probability for high-based shower and thunderstorm activity is north of a Cheyenne to Alliance line. Forecast soundings show quite decent moisture content in the mid to upper atmosphere this afternoon, such that NAEFS mean PW values are actually near the climatological 90th percentile. Still, this will be on top of a deep and very hot inverted-v sounding in the boundary layer. So, while true dry thunderstorms are not expected, the wind is likely to be more notable than the rainfall today. In fact, the Storm Prediction Center has included much of our High Plains in a Marginal Risk for severe wind gusts with the dry (ish) microburst threat. Increasing cloud cover and some cooling associated with evaporation of the falling rainfall may keep highs a few degrees cooler than forecast in a few locations, but it is tough to say exactly where this will occur.

Modest forcing in place of weak elevated instability will likely keep some shower activity going well into the evening hours today. This will actually provide an excellent setup for heat bursts this evening. After sundown, a very shallow surface inversion will develop with a well-mixed layer perhaps just 100-200m above the surface. Downdrafts associated with dissipating showers and thunderstorms could then actually lead to an increase in surface temperature this evening after the shallow inversion develops. Don't be surprised to see a few locations seeing gusty winds and temperatures above 90 degrees between 8PM and midnight tonight. Sunday will also bring a chance for high-based showers and thunderstorms but synoptic forcing looks a little weaker, which will probably lead to lower coverage compared to today. Gusty winds with potential for heat bursts continuing well into the evening will be the primary concern once again tomorrow.

By Monday, the upper level ridge will shift ever so lightly off to the east of the Four Corners, allowing for an improved tap of monsoon moisture to surge northward. This will increase chances for locally heavy rainfall and perhaps a few isolated strong to severe thunderstorms with the typical PM scattered showers and thunderstorms. However, NBM probabilities look a little too aggressive at this time, and were toned back to PoPs around the 40 to 60% range for most of the area.

LONG TERM /TUESDAY THROUGH FRIDAY/

Issued at 400 AM MDT Sat Jul 25 2026

Ensembles are in fairly good agreement showing PW peaking on Tuesday across the area with the latest monsoon surge. Rainfall chances will remain elevated as the powerful ridge recedes ever so slightly. While we are not expecting temperatures to fall below average, we should see the heat ease to slightly more reasonable values only about 5F above seasonal norms by Tuesday. This will be the theme for much of the weak beyond Tuesday as 700-mb temperatures remain generally in the +16 to +19C range. On the synoptic scale, the powerful ridge will begin to retrograde westward and also broaden its horizontal extent. The result of this is a reduction in the quality of the monsoon moisture plume as the week progresses. Recycled moisture trapped underneath the ridge will continue to produce daily chances for showers and thunderstorms Wednesday onwards, but expect PW to decrease gradually each day with a little lower overall thunderstorm coverage.

AVIATION /12Z TAFS THROUGH 12Z SUNDAY/

Issued at 529 AM MDT Sat Jul 25 2026

South to southwest winds will develop by midday with gusts to around 20 knots expected. Look for scattered high-based showers and thunderstorms to develop across a wide portion of the area during the afternoon, with multiple rounds expected through the late evening hours. While the primary hazard with this activity will be microburst winds, lightning, and brief VIS drops do to rainfall are also possible. By mid-evening, expect thunder to be less common, but gusty showers may continue until nearly midnight. Timing remains difficult to pinpoint as this activity will be disorganized and will come with multiple rounds. PROB30 groups were narrowed somewhat with this update. Most gusts will be in the 25 to 40 knot range, but a few isolated wind gusts exceeding 50 knots are possible near showers and storms.

CYS WATCHES/WARNINGS/ADVISORIES

WY...Heat Advisory from 11 AM this morning to 9 PM MDT Monday for WYZ101-102-107-108-118-119. NE...Extreme Heat Warning from 11 AM this morning to 9 PM MDT Monday for NEZ002-095. Heat Advisory from 11 AM this morning to 9 PM MDT Monday for NEZ003-019>021-054-055-096.