textproduct: Cheyenne

KEY MESSAGES

- Accumulating snow through Monday afternoon with Winter Storm Warnings for many of our high elevation and mountain zones and Winter Weather Advisories for nearby zones.

- 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.

SHORT TERM /THROUGH WEDNESDAY NIGHT/

Issued at 302 PM MDT Mon May 18 2026

On the backside of the strong system moving up into Nebraska we should see snow and precipitation beginning to subside into the evening hours. Strong pressure gradients did produce significant wind gusts and, combined with the heavy wet snow, near to blizzard conditions were noted this morning, particularly in Carbon County, shutting down I-80 and leaving several people without power across the area. Moving into this evening and overnight, we'll see concerns shift to cold temperatures as the cold airmass in place combined with snowpack or clearing skies helps to produce near to possibly record low temperatures. The entire forecast area is under a freeze warning due to this expected cold, with temperatures in the teens to mid 20's all the way through the Nebraska Panhandle. Cold sensitive plants, crops, and equipment will be impacted notably by this freeze.

After this, look for a slow warming trend through Wednesday as our pattern advects warmer temperatures from the southwest as we stay generally under weak troughing aloft with southwesterly to westerly flow at 500mb prior to the next quick hitting system at the end of the week. Both Tuesday and Wednesday will feature small embedded shortwaves which could produce some scattered showers or possibly even a weak thunderstorm, but overall activity looks to remain minimal and fairly inconsequential. As temperatures steadily rise the region will slowly warm, but don't expect a quick shot of warmth. Highs Tuesday reach into the 40's to 50's outside of Carbon County where the lingering snowpack will likely keep the area cool in the 30's for the day. Tuesday night into Wednesday lows will once again descend into the 30's east of the Laramie Range, while to the west we'll see another hard freeze in the teens to 20's (also including Converse County to the north). A Freeze Watch has been issued for tomorrow night, with an upgrade to warning likely. Moving into Wednesday highs continue to recover into the 40's to 60's, with lows back into the 30's to 40's with sub-freeze temperatures once again west of the Laramie range.

LONG TERM /THURSDAY THROUGH MONDAY/

Issued at 302 PM MDT Mon May 18 2026

Heading towards the end of the work week, a shortwave trough will push through Southeastern Wyoming and Western Nebraska on Thursday providing a source of large-scale forcing for ascent. Ensemble guidance has PWAT around the 75th percentile relative to climatology in addition to median SBCAPE around 300 J/Kg, so showers and thunderstorms are a good bet later in the afternoon and evening. Effective bulk shear is progged to range from 25-30 knots, so widespread severe thunderstorms are not expected, although can't rule out a few storms producing marginally severe gusty winds and hail. Given the increased cloud cover later in the day, high temperatures are expected to be 5-10 degrees below climatology in the 60s east of the Laramie Range, and 50s west. A secondary vorticity maximum will propagate across our region on Friday, combined with PWAT near the 60th percentile, resulting in another chance for a few showers and thunderstorms with little change in high temperatures from the previous day given the cloud cover.

Into the weekend, 500 mb heights rise as weak longwave ridging establishes itself across the Rocky Mountain West, resulting in a warming trend and mostly dry conditions. High temperatures are expected to be near climatology (average high in Cheyenne on May 23 is 67 degrees), with 60s west of the I-25 corridor and 70s further east. The warm up will continue Sunday into Monday as the ridge axis shifts over Wyoming, resulting in above-average temperatures and little to no chances of precipitation.

AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/

Issued at 525 PM MDT Mon May 18 2026

Snow and rain activity will continue at terminals for at least the next four to six hours as the shortwave trough moves northeast. Periods of IFR to LIFR conditions may still occur until this activity subsides. Winds become variable at the southeast Wyoming terminals overnight and into the morning hours. Ceilings are expected to lower at these terminals, possibly dropping to 300-500 feet with mist or fog. After about 16z ceilings should begin to improve and cloud cover thins. At the Nebraska Panhandle terminals ceilings should begin to improve overnight with winds becoming more northwesterly. Clouds also thin during the morning hours to mostly cirrus coverage.

CYS WATCHES/WARNINGS/ADVISORIES

WY...Freeze Warning from midnight tonight to 10 AM MDT Tuesday for WYZ113. Freeze Warning until 10 AM MDT Tuesday for WYZ101-102-106>108- 115>119. Winter Weather Advisory until 6 PM MDT this evening for WYZ101- 105-106-110-111-115-117. Freeze Watch from late Tuesday night through Wednesday morning for WYZ101-115. Winter Storm Warning until 6 PM MDT this evening for WYZ103- 104-109-112-114-116. Freeze Warning until noon MDT Tuesday for WYZ104-105-109>111. Freeze Watch from Tuesday evening through Wednesday morning for WYZ104-105-109>111-113-116. NE...Freeze Warning from midnight tonight to 10 AM MDT Tuesday for NEZ002-003-020-021-054-055. Freeze Warning until 10 AM MDT Tuesday for NEZ019-095-096.