textproduct: Cheyenne

KEY MESSAGES

- Widespread showers and storms are expected over the next several days. Monsoon moisture will lead to heavy rain with the potential for flash flooding. Isolated severe storms will also be possible.

- Numerous to widespread beneficial showers and scattered thunderstorms will occur Thursday afternoon and evening, with lesser coverage of late day shower and thunderstorm coverage for Friday through the weekend and into early next week.

- Maximum temperatures will be moderated by clouds and precipitation coverage for Thursday, then hot temperatures and possible Heat Advisories will return for Friday through Tuesday, east of I-25, due to lesser coverage of late day showers and thunderstorms and cloud cover. Maximum temperatures over the weekend and early next week will range from 90 to 105 degrees east of I-25, with mid 80s to near 90 degrees west of I-25.

SHORT TERM /THROUGH WEDNESDAY NIGHT/

Issued at 203 PM MDT Tue Jul 21 2026

The core of the upper level ridges is kind of centered over the Oklahoma Panhandle/NW Texas area. Due to the clockwise motion of the High this funnels all the warm pacific moisture into the Intermountain West. This translates into an abundant source of mid level moisture that will get translated toward the surface through daily afternoon storm chances and diurnal mixing within the boundary layer. Over the course of today and Wednesday, precipitable water (PWAT) will bouncing between the 90 and 99th climatological average at around 1 to 1.5 inches. NAEFs also shows strong 90th- 99th percentile Integrated Vapor Transport (IVT) as well to really capture the monsoonal moisture coming up from the South. With this abundant moisture weak thunderstorms will be starting to redevelop this afternoon. These showers/thunderstorms will be rather pulsy with the lack of shear and projected CAPE values around 1000 joules. Mid-level lapse rates are also expected to be kind of neutral this afternoon at around 7.5 C/km. So these showers/thunderstorms are going to very hit or miss as to whether they produce lightning but surely aren't expected to go severe. However, there are some potential ponding and flooding in low lying areas across the forecast area today especially near the WY/NE border where NAEFS expects the highest IVT values to be. And this is mostly due to also the lack of mid-upper level wind to really push these storms along.

Wednesday will be a wash, rinse, repeat of today. Some lingering showers will be possible in the morning. But the "main show" will be in the afternoon. There looks to be a little more synoptic forcing as well as MUCAPE pockets ranging between 1000-1500 joules. Once again there is virtually no shear so some a severe storm aspect, the CAPE is kind of wasted in this environment. However, with it being the Intermountain West I can't rule out so BB to pea-sized hail if one of the thunderstorms temporarily pulses up. The also big difference is that the IVT and Moisture content will be a little stronger than today so there's a bigger risk for potential flooding from these slow moving storms. Putting out a flood watch and matching our neighbor office Riverton was on the mind. However, their storms are likely to be stronger than ours with more of a chance for torrential downpour to lead to flash/localized flooding. WPC Excessive Rainfall Outlook does have a slight risk for us West of the I-25 corridor and a Marginal risk for areas along and east of I-25.

LONG TERM /THURSDAY THROUGH TUESDAY/

Issued at 203 PM MDT Tue Jul 21 2026

Thursday...More beneficial rains are anticipated as a decent positively tilted shortwave trough aloft passes overhead near peak heating, and with beaucoup, plenty of low and mid level moisture and decent upslope southeast winds advecting low level moisture northwestward, expect to see numerous to widespread showers with scattered thunderstorms in the afternoon and evening, focused once again along the I-25 corridor and near the mountains where orographics will coincide with the best 850/700 mb theta-e ridge axis. POPS along the spine of the Laramie Range and the Interstate 25 corridor will range from 60 to 90 percent, and weak steering flow aloft seen near 700 mb, around 10,000 feet Mean Sea Level, MSL, will aid in some locally heavy rainfall and some training of storms.

Friday...Will see an abrupt cutoff to the low and mid level moisture supply as drier air at low and mid levels advects into our counties as the dominant ridge over Colorado and southern Wyoming reasserts itself. Thus dry and hotter.

Saturday through Tuesday...Isolated to scattered afternoon and evening showers and thunderstorms expected, with areal coverage increasing each day due to increased mid level moisture. Fortunately, more beneficial rains expected concentrated over and near our Snowy, Sierra Madre and Laramie Ranges, with the best chances for convection on Monday and Tuesday. Typical weak northwest flow aloft on the northeast periphery of the ridge aloft will aid in occasional passing shortwave troughs aloft near peak heating resulting in increasing convective potential each day

AVIATION /00Z TAFS THROUGH 00Z THURSDAY/

Issued at 529 PM MDT Tue Jul 21 2026

The dominant ridging of the past few days will continue to weaken slightly and transition centered over northern Texas, while low and mid level pseudo monsoonal moisture increases over our counties, along with moist upslope east and southeast winds near the surface, advecting low level moisture northwestward into southeast Wyoming. Scattered to numerous afternoon and evening showers and thunderstorms will affect locations west of I-25 primarily this evening, with lesser coverage east of I-25.

Wyoming TAFS...For KRWL and KLAR, high confidence in scattered showers and thunderstorms in the 00Z to 03Z timeframe, per the NAM and HRRR models. Went with PROB30 at KRWL and TEMPO at KLAR as the convection evolves. Strongest thunderstorms will produce gusty and erratic wind gusts to 40 knots along with brief MVFR visibilities. Clouds will decrease later this evening. Expect typical gusty diurnal winds until sunset and after sunrise on Wednesday.

For KCYS, NAM and HRRR show convective potential holding off until the 05Z time frame, and confidence is moderate on much convection reaching KCYS after 00Z, so maintained a TEMPO for now from 02Z to 05Z. VFR prevails with scattered to broken clouds from 6000 to 10000 feet AGL. Will see typical gusty diurnal winds to 30 knots until late this evening.

Nebraska TAFS...Using the NAM and HRRR for timing, it appears that widely scattered to scattered showers and thunderstorms will develop or propagate across the terminals in the 03Z to 09Z timeframe, with lesser chances at KSNY, though high enough chances to include VCTS there. VFR prevails with scattered to broken clouds near 6000 feet prevailing. Will see typical gusty diurnal winds up to 25 knots until early this evening, and again after 15Z Wednesday.

CYS WATCHES/WARNINGS/ADVISORIES

WY...None. NE...None.