textproduct: Cheyenne

KEY MESSAGES

- Numerous to widespread showers and thunderstorms are expected Wednesday through Thursday. There is an Enhanced Risk for severe thunderstorms over the eastern plains, mainly along and east of Interstate 25, including western Nebraska.

- Very large hail (up to 4 inches in diameter), strong damaging winds, and a few tornadoes are possible Wednesday afternoon and evening.

- Thunderstorms Wednesday and Thursday will also increase the flash flood potential, particularly over recent burn areas.

- Warming temperatures, falling humidity, and increasing winds will increase fire weather concerns this weekend into early next week.

SHORT TERM /THROUGH FRIDAY/

Issued at 204 AM MDT Wed Jun 24 2026

Yet another active day expected for Wednesday, and possibly Thursday, with deep low to midlevel moisture remaining over the area. For early this morning, last night's thunderstorms have moved southeast into northeast Colorado with some activity remaining near Sidney as of 300 AM. Low clouds and some fog have formed behind this thunderstorm activity as low level winds shift into the east and southeast early this morning. Already observing visibility between 1 to 3 miles in patchy fog and dewpoint climbing into the mid 50s, which will set the stage for a busy afternoon and evening. Over the next 6 hours, should be relatively quiet as the low stratus and fog resulting in boundary layer CIN of -200 to -400 j/kg over the area.

SPC has upgraded the area from a Slight Risk (2/5) to an Enhanced Risk (3/5) Wednesday afternoon and evening over most of the southeast Wyoming eastern plains and most of the western Nebraska panhandle. In addition, the Marginal and Slight Risk for excessive rainfall have been extended and increased in coverage for training thunderstorms along a potent cold front near the Colorado/Wyoming border in addition to any outflow boundaries that run parallel to the mean flow aloft and surface cold front. This may be one of the more active days in this area for the past few years due to several severe weather concerns. Model soundings and mesoscale analysis show PWAT values between 1.00 to 1.33 inches over a bulk of the area. A quick look at NAEFS shows PWAT values, even for this time of the year, above the 98th percentile and nearing the weekly maximum for 00z and 06z. Shear will be the least of our concerns with this event, with all models showing plentiful 40 to 60 knots of 0-6km shear (effective shear even higher). Impressive sounding profiles with peak lapse rates within the primary hail growth zone (0 to -20c or roughly 10k to 25k feet AGL) on both the GFS and NAM soundings. As long as we break the cap, CAPE will be plentiful in this set up with most models and ensemble guidance showing MLCAPE of 1000 to 2000 j/kg and SBCAPE of 1500 to 2500 j/kg...even up to 3000 j/kg in the most unstable scenarios. Low level wind shear is also present with a veering wind profile in the lowest 2 km, which becomes even more impressive in the vicinity of the surface cold front later this afternoon. The only thing that may reduce the overall threat today will be the large amounts of CIN early in the day, which may take a while to erode. However, the forcing along the front should be sufficient enough to break this cap in the afternoon, and this may happen fairly quickly/suddenly. All models of severe weather are possible, including tornadoes. Very large hail is also looking more likely given the steep lapse rates in the hail growth zone and the favorable shear profiles. Would not be surprised to see a few softball-sized hail reports today.

If that wasn't enough, concerns for flash flooding are increasing, not only today...but for Thursday as well (even though storm motion should be quicker on Thursday). Thunderstorm cells that train southeast near the cold front and slowly propagate and redevelop near outflow boundaries could become a problem this afternoon and evening. Therefore, going to start messaging the flash flood threat, very large hail threat, and tornado threat more aggressively today.

For Thursday, along with the Flash Flood threat continuing due to the cold front stalling near the I-25 corridor, there is a slight risk of severe thunderstorms over most of the forecast area. However, this risk may be more of a severe wind threat with high res guidance showing several bands of squall lines moving east across the area. WAA aloft near the front may get this activity going early in the day with upslope flow remaining near the surface, possibly as early as 300 to 800 AM up north. In the afternoon, the HRRR shows what appears to be either a strong squall line or derecho rapidly moving southeast over southeast Wyoming and western Nebraska into the evening hours with an impressive low level cold pool on 36 hour surface analysis. Other CAMs show more in the way of individual bow echo segments as the line move southeast, but not as continuous nor as intense as the HRRR. Stay tuned for updates on a potential strong (convective) wind threat for Thursday.

LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/

Issued at 230 PM MDT Tue Jun 23 2026

Thursday...Westerly flow aloft continues, and with surface low pressure developing over south central Wyoming producing a convergence axis from Douglas to Laramie, and plenty of low and mid level moisture, and 850/700 mb theta-e ridge axis from Casper to Cheyenne, along with CAPE of 1000 to 1800 J/kg and bulk shear near 50 knots, we anticipate some storms to become severe, with large hail and damaging winds as the primary threats east of I-25, with some locally heavy rainers due to flow aloft.

Friday...Low amplitude ridging develops over our forecast area, with some drier air noted advecting in. However, still expect isolated to widely scattered afternoon and evening thunderstorms to form along a low level convergence axis along the I-25 corridor. A few strong and possibly severe storms may occur.

Saturday...The flow aloft turns southwest and increases in speed, with considerably drier air moving across our counties, producing a dry day with a warming trend as 700 mb temperatures spike near 19 Celsius.

Sunday through Tuesday...A broad trough aloft develops across the northern and central Rockies, with dry southwest flow aloft, leading to only isolated to widely scattered thunderstorms at most in the afternoons and evening. Slightly cooler compared to Saturday in the wake of a cold frontal passage.

AVIATION /12Z TAFS THROUGH 12Z THURSDAY/

Issued at 600 AM MDT Wed Jun 24 2026

Low clouds and patchy fog will continue early this morning, mainly for the eastern plains of southeast Wyoming and western Nebraska. These clouds/fog are expected to lift with another round of severe thunderstorms possible for most terminals mid to late afternoon through the late evening hours.

HAZARDS/WEATHER TRENDS: MVFR to IFR CIGS and fog will continue until 16z before lifting by 18z, mainly over KCYS and all of the western Nebraska terminals. Thunderstorms will begin to develop between 19z and 22z. Kept PROB30 groups for most terminals late this afternoon and this evening (22z today to 05z Thursday) for showers and severe thunderstorms. Will continue to add VCTS and TEMPO groups, and possibly prevailing conditions, as coverage and timing becomes more certain over the next few hours. Expect low CIGS and fog to redevelop after 06z tonight after the thunderstorms are finished for the night.

CYS WATCHES/WARNINGS/ADVISORIES

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