textproduct: Cheyenne

KEY MESSAGES

- Severe weather will be possible Sunday afternoon with a Marginal Risk of strong to severe thunderstorms along the Interstate 80 corridor.

- Another round of accumulating late season snow is increasingly likely on Monday, mainly above 5000 feet in elevation.

- Near record cold Monday and Monday night will lead to widespread freezing temperatures, which may damage sensitive vegetation and outdoor irrigation systems.

- Slow warming trend by the mid to late week with temperatures near normal by Thursday and Friday. Chance of showers and a slight chance of thunderstorms each day through Friday evening.

..Very cold into Tuesday

Thankfully, this storm system won't stick around for too long as it will already be in its weakening phase by Monday afternoon, as the remnant open wave trough quickly ejects east over the area. Snow or rain/snow mix will gradually come to an end mid to late Monday afternoon. With that said, impacts will not complete go away with a remaining snowpack likely and possibly some clearing skies. Expect record low temperatures or near- record low temperatures Monday night and early Tuesday morning with temps possibly lowering into the teens to low 20s. Expect far eastern Wyoming and western Nebraska to be slightly warmer with the lack of a snow pack, but still could see record lows in the mid to upper 20s. This classifies as a very late hard freeze for the region and we'll likely need Freeze watches or warnings shortly. For now, will see how the event plays out before committing. Plus it's still 4 to nearly 5 periods out, so we have some time to make additional adjustments.

LONG TERM /TUESDAY THROUGH SATURDAY/

Issued at 216 PM MDT Sat May 16 2026

The long term period will begin under an anomalously cold air mass in the wake of a powerful winter storm, with record low temperatures across Eastern Wyoming and the Nebraska Panhandle on Tuesday morning (record low for Cheyenne on Tuesday is 27 degrees set back in 1966). Unsurprisingly, high temperatures on Tuesday will remain 15-20 degrees below climatology mainly in the 40s west of the Laramie Range, and 50s east, as we remain under the influence of a broad, positively-tilted trough centered over the Rocky Mountain West. Areas with the most snow cover will be the coldest spots, as snowfall has a high albedo and is highly effective at radiating back into space. Further, melting and sublimation of snow are cooling processes, so this will further limit warming even given the high May sun angle. Tuesday night will again feature record low to near record low temperatures as we remain under weak isentropic descent and cold air advection with partly clear skies which should allow for another night of effective radiative cooling.

The gradual warm up continues as we head into Wednesday and are situated in a zonal flow regime as well as in the left-entrance region of a departing 90-100 knot 250 mb jet, which isn't exactly a favorable relative location for widespread ascent and precipitation. However, given that numerous vorticity maxima will be propagating along the base of the trough combined with differential heating of the sloped terrain, chances for a few high-based showers and thunderstorms are in the forecast. These are likely to produce more wind than beneficial rain (it is Wyoming, of course) as forecast soundings are showing inverted-V profiles and MUCAPE around 100 J/Kg.

Thursday we see another shortwave trough propagate within the longwave pattern, so chances for high-based showers and thunderstorms will remain in the forecast as high temperatures creep back up towards climatology in the low to mid 60s. Flow turns more northwesterly into Friday, however with the absence of any large- scale forcing for ascent, conditions will remain mostly dry with high temperatures around seasonal values.

AVIATION /12Z TAFS THROUGH 12Z MONDAY/

Issued at 615 AM MDT Sun May 17 2026

Active over the next 24 to 30 hours. Strong storm system digging south out of Canada will be located across the Great Basin region later today. Ahead of it, several rounds of showers and thunderstorms are expected...including early this morning with the stronger activity likely in the afternoon. With a potent cold front moving southeast across the area, expect winds to shift into the north and becoming gusty this morning and afternoon. Rain will gradually change to snow late in the TAF period for KRWL, KLAR, and after 06z for KCYS.

HAZARDS/WEATHER TRENDS: Increasing confidence of VFR conditions for a part of today with a break in the showers and thunderstorms between 15z and 20z. MVFR CIGS and VIS expected at KLAR and KCYS over the next few hours as a band of thunder showers move east across the area. The next band of showers and thunderstorms expected to develop early this afternoon and move east or northeast across the plains. Multiple lines of heavy rainfall are possible after 21z with brief IFR conditions and gusty winds. Rain will change over to snow later tonight with IFR conditions expected at KRWL between 06z and 09z, and after 09z for KLAR and KCYS.

CYS WATCHES/WARNINGS/ADVISORIES

WY...Winter Weather Advisory from midnight tonight to 6 PM MDT Monday for WYZ101-105-106-117. Winter Storm Warning from 6 PM this evening to 6 PM MDT Monday for WYZ103-104-110-114-116. Winter Storm Warning from midnight tonight to 6 PM MDT Monday for WYZ109. Winter Weather Advisory from 10 PM this evening to 6 PM MDT Monday for WYZ112. NE...None.