textproduct: Cheyenne

KEY MESSAGES

- There is a Marginal Risk (Level 1 of 5) for severe weather this afternoon and evening over portions of the High Plains. Isolated large hail and damaging winds are the primary concerns.

- Friday will be cool and breezy with showers ending in the morning hours. Expect freezing temperatures in Carbon and Albany county Friday morning, with lows in the 30s elsewhere.

- A warming trend will carry through Memorial Day weekend, with near record high temperatures possible by Monday.

- Isolated high-based showers and storms will be possible each day over the long weekend but rainfall will be limited. Rainfall potential will increase on Tuesday and Wednesday.

SHORT TERM /THROUGH FRIDAY NIGHT/

Issued at 210 PM MDT Thu May 21 2026

A potent upper level trough is swinging across Wyoming this afternoon, which will support active weather through early Friday morning. ahead of the primary forcing, we have a dryline boundary setup from roughly Cheyenne to Fort Laramie to the WY/NE/SD triple point. Southerly winds east of the boundary are advecting in good low-level moisture, while drier air and westerly flow dominates to the west. The dryline is providing a focus for some pre-frontal convection, with several storms already kicking up. The environment ahead of these storms is favorable for isolated strong to severe thunderstorms, with SBCAPE around 1000 to 1600 J/kg and 20-40 knots of effective bulk shear. Vertical wind shear increases further south, and the most favorable environment for storms is located in the southern Nebraska panhandle. The overall hazards for today remain unchanged, with strong, gusty winds and isolated large hail the primary concerns. An isolated tornado cannot be ruled out, particularly in the southern panhandle. Expect multiple rounds of showers and thunderstorms this afternoon and evening. Coverage will greatly increase over the next few hours as forcing associated with the approaching trough increases. Current thinking is that the primary severe threat will be associated with the initial round of dryline convection, whereas the strongly forced second round about to move into Carbon county will have lower chances for severe, but high coverage of rainfall and gusty winds. The window for discrete storms (and the primary severe threat) should conclude around 8PM to 10PM. The progression of the strong forcing will move eastward slowly, likely not reaching the edge of the forecast area until around 10PM to midnight tonight. This will still have the potential to produce locally heavy rainfall and gusty winds. Showers with synoptically driven gusty northwest winds will continue behind the main line, mainly north of the North Platte River Valley. This will continue into Friday morning. Chadron will be the last area to dry out, but expect rain to conclude by noon. This lingering shower activity will be driven by a narrow TROWAL developing in the wake of the potent upper level low tonight.

As the surface front moves through this evening, expect gusty northwest winds to spread across the area. The probability for high winds is low (20% or less), but we can expect to see fairly widespread wind gusts of 35 to 50 mph, lasting into the day on Friday. This front will enforce the chilly airmass over the area, causing much of the area to fall back into the 30s again tonight. Around Cheyenne, Douglas, and Lusk, look for lows around 32 to 35. This may stress sensitive vegetation, but confidence in dropping below freezing not high enough for a Freeze Warning (30 to 50% probability). In addition, the gusty winds should limit frost formation. Further west, particularly where snow cover lingers, cold air advection will support higher probabilities of a freeze (70 to 90%). Winds will also be lighter, mainly in Carbon County, which should improve radiative cooling. Therefore, confidence was high enough to issue a Freeze Warning for the valleys of Carbon and Albany county. Heading into Friday afternoon, high temperatures will be similar or slightly cooler than today for most of the area. Another weak vort-max will approach the area from the west Friday afternoon, which will increase cloud cover over our western areas, and also lead to a slight chance for a few showers mainly tied to the higher terrain. This will linger into the evening hours, and possibly creep eastward along the Colorado state line into the High Plains overnight.

LONG TERM /SATURDAY THROUGH THURSDAY/

Issued at 210 PM MDT Thu May 21 2026

After this trough pushes through into the Northern Plains on Friday, A weak upper level ridge starts to build over the Intermountain West. Southeast Wyoming and the Nebraska Panhandle will largely be dry this weekend as there will be limited vorticity and decent lift to play with. However, some diurnal afternoon showers may be possible, but mostly confined to the southern half of the forecast area Saturday and Sunday. By Monday the synoptic pattern starts to shift as a progged Low pressure system starts to push into Baja California with another northern system to pushes into the Pacific Northwest. This will push us into a southwest advecting in some moisture from the Pacific and some dry air from the downsloping winds off the mountains near the surface. As these two systems push into United States the southern system almost gets absorbed by the northern system to form this deep trough to kick start our wet pattern again on Tuesday most likely in the afternoon. Thanks to our summer sun, the synoptic set up of this deep trough will lead to decent destabilization of the atmosphere and produce scattered thunderstorms for the afternoon and evening. The models really start to diverge with the synoptic pattern after Wednesday morning. The GFS has a tilted ridge working its way into the Intermountain West possibly drying us out or we can go with the Euro or Canadian that have systems of varying intensities keep us rainy and stormy throughout the week. It will be interesting to see how the models trend past our Tuesday trough.

AVIATION /00Z TAFS THROUGH 00Z SATURDAY/

Issued at 555 PM MDT Thu May 21 2026

Severe thunderstorms have been impacting mainly the Nebraska terminals this afternoon, resulting in visibilities as low as 3/4 mile in the heavier showers and thunderstorms, as well as CIGS below 500 feet, yielding LIFR. Expect similar conditions to remain in place before 06Z as some of the stronger storms move off to the east of our area. Overall expect thunderstorm coverage to decrease after this time, however cannot rule out a few rumbles of thunder as forecast soundings still show some weak instability (< 300 J/Kg MLCAPE). Showers are expected to continue through the overnight period as a potent shortwave trough begins to exit our region.

Surface cold front moves through later this evening shifting our winds to northwesterly. Can expect a quick ramp up in our winds after 06Z, with gusts as high as 30-35 knots for the Nebraska terminals and KCYS. Sustained winds are expected to range from 20-25 knots before the surface pressure gradient weakens and winds relax to 15-20 knots after 21Z. High confidence that CIGS lift and VFR will prevail after 15Z.

CYS WATCHES/WARNINGS/ADVISORIES

WY...Freeze Warning from midnight tonight to 9 AM MDT Friday for WYZ104-105-109>111-113-115-116. NE...None.