textproduct: Cheyenne

KEY MESSAGES

- Dry conditions will persist through the end of the week, but a weak pressure gradient will promote slightly above normal temperatures with winds generally too weak for critical fire concerns.

- A return to more active weather will occur over the weekend and on Monday as a series of weather disturbances combine with adequate low and mid level moisture to produce scattered to numerous late day showers and thunderstorms.

- Somewhat drier air will move into the forecast area for Tuesday and Wednesday of next week, producing a decrease in areal shower and thunderstorm coverage, along with bringing a warming trend.

SHORT TERM /THROUGH SATURDAY NIGHT/

Issued at 202 AM MDT Fri Jun 19 2026

Benign weather will continue for today as weak ridging noses in from the southwest. This will help bring ample sunshine along with lighter winds, so expect highs this afternoon to soar into the low to mid 80s with lows Friday night dipping down into the 50s. Speaking of Friday night, that is when we will start to see some changes. First thing first, the weak ridge overhead will slide off to the east, as it does so, a surface a low will strengthen over east-central Colorado. This will help shift the surface flow to become southeasterly, which will allow ample moisture at low-mid levels to advect into eastern portions of our CWA. At the same time, most of the CWA west of the I-25 corridor will remain dry with a dry airmass firmly in place.

Lets shift focus to the main event in the short term period, Saturday. With the aforementioned surface low pumping in moisture, coupled with an upper-level shortwave sliding across the CWA as the ridge moves off to the east, these features will help bring in the potential for severe weather by Saturday afternoon. Taking a look at a few other severe indices, model guidance is showing Convective Available Potential Energy (CAPE) values upwards of 2000 J/KG while Lifted Indices (LI) around -6, combined with a few other favorable parameters, strong to severe thunderstorms are likely to develop and impact portions of eastern Wyoming and the Nebraska Panhandle by Saturday afternoon. Most of this development should remain east of the I-25 corridor, with southern portions of the Nebraska Panhandle, including Sidney, having the greatest threat of severe weather. Therefore, the Storm Prediction Center (SPC) introduced a slight risk (2 of 5) for this area and a marginal risk (1 of 5) for the remainder of the CWA as mentioned previously. All storm modes are possible of which may produce tornadoes, large hail, and/or strong winds, so stay tuned to the forecast for future updates. The other thing that can't be over looked, guidance is showing precipitable water values of an inch or more across eastern Wyoming and the Nebraska Panhandle, with this much moisture, a very serious threat of flash flooding is possible. The Weather Prediction Center (WPC) has a Marginal Risk (MRGL) for excessive rainfall that could indicate the high probability of the flash flooding potential across portions of the Nebraska Panhandle and far eastern Wyoming.

LONG TERM /SUNDAY THROUGH THURSDAY/

Issued at 111 PM MDT Thu Jun 18 2026

No major changes to the long term outside of removing Saturday to put in the short term and then starting the long term with Sunday from the previous discussion...

Sunday...While a shortwave trough aloft slides eastward across the Dakotas and Nebraska in the afternoon, its associated cold front will bring some heat relief with 700 mb temperatures near 7C suggesting maximum temperatures in the 70s to lower 80s. Continued adequate low and mid level moisture for scattered late day showers and thunderstorms, closer to the deeper moisture east of Interstate 25.

Monday...Looks like a similar setup compared to Saturday, with a shortwave trough passage in the afternoon, spawning scattered showers and thunderstorms for the afternoon and evening focused along a surface trough axis west of the Wyoming-Nebraska state line. Some strong to severe thunderstorms look likely due to expected instability and wind shear profiles, mainly for southeast Wyoming east of I-25. Upslope flow in the low levels will aid lift for storm generation.

Tuesday...Drier air infiltrates our forecast area under northwest flow aloft, allowing only isolated to widely scattered afternoon and evening showers and thunderstorms, primarily east of I-25. Temperatures slightly warmer than Monday with 700 mb temperatures near 11C.

Wednesday...Ridging aloft moves overhead inducing warmer high temperatures. A surface trough will develop east of I-25, with convergence along the trough aiding in isolated to widely scattered late day showers and thunderstorms east of I-25.

Thursday...Typical "beware" northwest flow aloft will prevail, with decent southeasterly low level winds advecting low level moisture northwestward across our eastern half of counties, and helping to spawn scattered showers and thunderstorms focused along a low level convergence axis. Decent shear and instability suggest possible isolated to widely scattered strong to severe thunderstorms in the afternoon and evening east of I-25.

AVIATION /18Z TAFS THROUGH 18Z SATURDAY/

Issued at 1126 AM MDT Fri Jun 19 2026

Later this afternoon the winds should switch to the east and then southwest to south in some place by 06z. By 08z Low clouds will start to push into the region from KCYS and east through tomorrow morning. After 18z tomorrow isolated to scattered thunderstorms are possible for KCYS and terminals east. Next TAF period will cover the thunderstorms.

CYS WATCHES/WARNINGS/ADVISORIES

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