textproduct: Cheyenne

KEY MESSAGES

- An unsettled weather pattern will continue this weekend with daily chances for afternoon/evening showers and thunderstorms as a potent upper level disturbance moves northeast over the area.

- Strong to severe thunderstorms will develop this afternoon for areas east of the I-25 corridor. If severe thunderstorms develop all hazards are possible; large hail, damaging winds, and tornadoes are possible.

SHORT TERM /THROUGH MONDAY/

Issued at 215 PM MDT Sat May 30 2026

Primary forecast concern over the next 48 hours is the potential for severe thunderstorms over far eastern Wyoming and western Nebraska this afternoon through late this evening. Potent upper level low clearly seen on IR and Visible Satellite over south central Wyoming is forecast to become a negatively tilted open wave trough over the next several hours. This trough axis will accelerate northward over eastern Wyoming and western Nebraska through early this evening. Current surface observations show ample moisture east of a line from Lusk Pine Bluffs, paralleling the Wyoming/Nebraska border. Activity has already started to form across far east central Wyoming and the northern Nebraska Panhandle where low clouds have dissipated earlier in the day. Further south, expect another round of thunderstorms to push across far southeast Wyoming and the southern Nebraska panhandle, which are now starting to form south of the Wyoming/Colorado border at this hour. This area will likely become our primary focus as it moves northeast into this evening. Upper level analysis shows strong upper level diffluence increasing rapidly late this afternoon along and east of I-25 as the base of the trough/vort max lifts northeast. Expect multicells and isolated supercells initially, with activity growing upscale once the vort max lifts north. Overall, expect a large hail threat (1.00-2.00 inches) and maybe an isolated tornado becoming a straight line wind threat through the evening hours. Could see some gusts up to 75 MPH with the strongest lines. A Severe Thunderstorm Watch has been issued mainly for areas east of Interstate 25 until 900 PM late this evening. Although cells will move north and northeast, expect any lines of thunderstorms to propagate eastward into this evening.

Further west, moisture is much more limited with dewpoints already dropping into the 30s this afternoon. Still expect isolated to widely scattered thunderstorms with a gusty wind threat into this evening before the cooler air, associated with the negatively tilted trough, moves east into central Wyoming. Once the trough lifts northeast, westerly winds will increase behind it with most models showing 700mb winds around 50 knots. In-house wind guidance shows 55% to 65% probability of high wind criteria for Arlington/Elk Mountain, with probabilities between 30% to 45% for Bordeaux and the I-80 Summit/foothills. With shallow convection over the Arlington area, and a possibility for gusty winds, decided to upgrade the High Wind Watch to a Warning and start it earlier (400 PM) in the day.

Thunderstorm activity should push east of our area by midnight, with left over showers before sunrise Sunday. Can't rule out some low clouds and patchy fog in areas that received heavy rain, but westerly winds will quickly increase towards morning limiting any fog threat. Other than High Wind concerns in and near the wind prone areas and breezy conditions elsewhere, quiet weather expected into Sunday with any thunderstorm activity staying well to the north of I-80 towards Douglas and Lusk. Not as cool with a slight warming trending...and high temperatures in the upper 60s (west of I-25) to low/mid 80s for western Nebraska.

For Monday, showers and thunderstorms should return to the high plains as surface winds shift into the south and southeast. Further west, another broad upper level trough will brush the northern Great Basin region and move into Wyoming later in the day. May see some strong to marginally severe thunderstorms with 0-6km shear around 35 knots and some low to midlevel instability.

LONG TERM /MONDAY NIGHT THROUGH SATURDAY/

Issued at 231 PM MDT Fri May 29 2026

The long term period will begin under broad SW flow aloft and a ridge axis located to our east over the Central Great Plains, with a large closed upper-level low situated over Montana. Tuesday will feature high temperatures of 5-10 degrees above climatology in the mid-upper 70s along and west of the I-25 corridor with mid-80s further east mainly across our Nebraska counties. With PWAT values around the 90th percentile and some weak IVT within the SW flow, can expect showers and thunderstorms as numerous weak impulses propagate around the base of the aforementioned closed system to our north. While the strongest deep-layer shear is expected to remain well to our north over SE Montana, effective bulk shear around 30 knots will result in a chance for a few severe thunderstorms, especially east of the Laramie Range where low-level moisture is expected to be highest. Although exact details are likely to change, ensemble guidance has a dryline located somewhere in the vicinity of the Wyoming/Nebraska border which could also provide a source for mesoscale forcing for ascent depending on the strength of the dryline circulation and the magnitude of capping. With the above- average high temperatures on Monday located upstream of SE Wyoming/W Nebraska across Western Colorado, SW aloft may advect a strong elevated mixed layer over our low-level moisture which may limit shower and thunderstorm coverage to the higher terrain, with lower elevations remaining capped. This will need to be monitored in short- term updates to address chances of severe weather on Tuesday.

Wednesday will feature weakening flow aloft as the closed system and associated belt of strong flow to our north lifts to the north and east over Canada. There should be enough remaining moisture underneath the ridge to allow for another round of diurnal showers and thunderstorms, however with an overall lack of large-scale forcing, these should be confined to the higher terrain. Weak mean cloud-layer flow underneath the ridge would also suggest little storm coverage over lower elevations. High temperatures on Wednesday will be similar to the day prior.

Heading towards the end of the work week, the longwave ridge flattens and mid-level flow becomes more zonal. As mid-level heights rise, we will also see a gradual warming trend along with mostly dry conditions. Some lingering moisture will allow for daily chances of showers and thunderstorms, although no widespread precipitation is anticipated through the end of the long term.

AVIATION /06Z TAFS THROUGH 06Z MONDAY/

Issued at 1110 PM MDT Sat May 30 2026

Primarily VFR conditions expected overnight as showers and storms move out of the are. There is a slight chance for a shower or two at KRWL over the next few hours, but all precipitation chances end by the early morning hours. Gusty winds are anticipated for the late morning into the afternoon hours. Expecting mostly clear skies for the afternoon.

CYS WATCHES/WARNINGS/ADVISORIES

WY...High Wind Watch through Sunday afternoon for WYZ106-116-117. High Wind Warning until 9 AM MDT Sunday for WYZ110. NE...None.