textproduct: Cheyenne

KEY MESSAGES

- Another round of thunderstorms will bring the potential for localized flash flooding and isolated strong to severe thunderstorms this afternoon and evening.

- A Flood Watch & Severe Thunderstorm Watch are in effect through this evening for much of the High Plains.

- Isolated strong to severe storms and localized flash flooding will remain possible Sunday, though overall storm coverage will be lower.

- Drier weather and temperatures close to seasonal averages will return early next week.

SHORT TERM /THROUGH SUNDAY NIGHT/

Issued at 216 PM MDT Sat Aug 15 2026

Another round of slow moving thunderstorms is in store for this afternoon and evening. Looking at Water Vapor, the mid and lower levels show plumes of moisture advecting through Colorado and Arizona and into our region. This will drive our PWAT values into the 1.0-1.25 inch range during the weekend as we are in Southwest flow. 700mb flow will remain rather slow today, with generally westerly to southwesterly flow expected. A messy, surface high pressure system will attempt to develop west of the Rocky Mountains over western Colorado before strengthening into the afternoon hours. With ample moisture available due to continued monsoonal moisture advection, the easterly flow will lead to very moist, upslope flow along and east of the Laramie Range. 700mb and 500mb vorticity maxima will be the major players in the synoptic forcing which is expected to increase into the later afternoon hours. Heavy rainfall is anticipated once again today, with the Weather Prediction Center placing portions of the region in a Slight Risk of excessive rainfall and a larger portion in a Marginal Risk of excessive rainfall. With the sustained rainfall across the lower elevations yesterday, the soils should be moderately saturated to aid in localized areal and urban flooding. A Flood Watch was issued on the overnight shift that is valid from 2PM through 10PM for nearly all locations along and east of the Laramie Range, where Precipitable Water values remain at and above the 90th percentile and moist, upslope flow persists. In addition to the flooding risk today, the Storm Prediction Center has placed far southeast Wyoming and western Nebraska in a Slight Risk (Level 2 of 5) of severe weather this afternoon. Primary hazards look to be isolated, large hail and damaging wind gusts. Isolated pockets of MLCAPE and SBCAPE around 1000 J/kg will provide enough instability for stronger updrafts to develop this afternoon, especially across western Nebraska. The biggest question will be whether or not the early morning cloud cover anticipated across the region puts a damper on the severe potential this afternoon. Pockets of clearing skies occurred across the forecast area to aide in some diurnal heating this morning and strengthening the instability for the showers/thunderstorms later. Forecasting the daily high temperatures and trying to get the hourly trend will be rather difficult as these clouds push into the region potentially cooling areas faster than the models could predict as well.

For Sunday, slightly drier condition as the upper-level flow turns a little more westerly, cutting off some of the monsoonal moisture advection into the area. However, with the ample moisture present over the past several days, plenty of residual moisture will be present to get another round of showers and storms Sunday afternoon into the evening hours. A few lobes of 500mb vorticity will advect across the region Sunday afternoon, providing some forcing for ascent. Slightly stronger 700mb warm air advection briefly develops Sunday afternoon, adding an additional forcing for ascent for showers and storms. Surface flow turns southerly Sunday afternoon through much of the overnight hours, leading to weak ascent across the Cheyenne Ridge, likely resulting in showers and storms developing in this area once again. Precipitable water values look to return towards more climatologically average values Sunday, decreasing the threat for isolated flooding across the region. However, with monsoonal moisture still in play, flooding potential continues for Sunday with a Marginal Risk of Excessive Rainfall from the Weather Prediction Center. Another round of strong to severe storms will be possible Sunday, with a Slight Risk of severe weather for much of the area and a small portion of the region under a Slight Risk of severe weather once again.

LONG TERM /MONDAY THROUGH FRIDAY/

Issued at 216 PM MDT Sat Aug 15 2026

Drier air will work into the area on Monday, bringing us a break in the stormy monsoon weather pattern. Expect mostly sunny skies to return to the area with temperatures generally near seasonal averages, in the lower 80s around Laramie and Rawlins, and mid to upper 80s along and east of I-25. While isolated showers and/or thunderstorms will still be possible, coverage will be significantly lower than the preceding days. The boundary layer will be much drier on the Wyoming side, which may lead to a dry microburst, threat, while a few actual rain producing thunderstorms will be possible mainly on the Nebraska side.

The monsoon tap recovers somewhat on Tuesday into Wednesday, though the flow will remain largely westerly aloft. Still, some low to mid level southerly flow over the Great Basin will help inject higher PW into our area, pushing values back to around 0.75 and 1.2 inches or so across the area. This will of course be not quite as high as the current monsoon surge, but should be sufficient to kick up coverage of showers and thunderstorms for Tuesday and Wednesday, especially with some help from an upper level shortwave trough riding over the top of the ridge Wednesday. While the boundary layer will still b on the dry side during this period, there looks to be plenty of moisture aloft so rain should still reach the ground even in the drier areas. Tuesday should see temperatures climb just a smidge above seasonal averages, while these values will fall by a few degrees Wednesday with the aforementioned shortwave.

The upper level ridge will amplify to our west on Thursday, and Friday, turning the flow aloft to a more dry, northwesterly flow. Expect storm chances to become much more isolated once again as temperatures climb back above seasonal averages. An early look at 700-mb temperatures appears fairly marginal for record highs with this round with NAEFS means hovering around +15 to +18C, or near the climatological 90th percentile.

AVIATION /00Z TAFS THROUGH 00Z MONDAY/

Issued at 600 PM MDT Sat Aug 15 2026

Heavy showers and thunderstorms are ongoing across the eastern plains late this afternoon and should continue into this evening. Activity may linger past 03Z, but confidence is limited at this time due to poor model agreement and very isolated coverage. Low CIGS and fog will be the primary concern between 05z and 12z Sunday before another round of thunderstorms impacts the region Sunday afternoon.

HAZARDS/WEATHER TRENDS: Primary concern is thunderstorms with strong gusty winds, very rainfall, and LIFR conditions over the next 3 hours (00z to 03z). Kept TEMPO and prevailing groups for higher confidence or activity already across the terminal, with PROB30 for lower confidence. After 03z, expect patchy coverage of lower CIGS with the possibility of fog for KCYS, KAIA, KBFF, and KSNY between 06z and 12z Sunday.

Another round of thunderstorms expected after 20z Sunday, but coverage is expected to be much more isolated, so will keep out of the TAF for now.

CYS WATCHES/WARNINGS/ADVISORIES

WY...Flood Watch until 10 PM MDT this evening for WYZ102-107-108- 117>119. NE...Flood Watch until 10 PM MDT this evening for NEZ002-003- 019>021-054-055-095-096.