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.

UPDATE

Issued at 449 AM MDT Mon May 18 2026

Monitoring blizzard conditions over the northern Snowy Range Foothills at this hour. Current observations along the Interstate 80 corridor from Walcott Junction to Arlington show visibility as low as 1/8th of a mile with winds gusting 50 to 65 MPH. Going to give this another hour or so, and then may need to upgrade to a Blizzard Warning if this continues. Also monitoring central Carbon County with similar conditions just starting in and around Rawlins.

SHORT TERM /THROUGH TUESDAY/

Issued at 255 AM MDT Mon May 18 2026

Late season winter storm ongoing across southeast Wyoming with everywhere above 6500 feet changing to snow within the last 3 hours. Rain/snow line is roughly 10 miles west of Cheyenne at this hour based on area webcams which show snowfall at the Warren Exchange along I-80. Most of Interstate 80 west of there shows very difficult travel conditions with some of the worst conditions on the I-80 Summit, which is currently experiencing visibility below one half mile in heavy snow. Snow is starting to accumulate on the roads above 7000 feet and expect this to continue through much Monday morning. Storm system is just starting to intensify at this hour...as seen by the current IR Satellite loop with cooling cloud tops over most of Wyoming and the distinct "comma cloud" beginning to take shape. No changes yet to Winter Weather headlines, but will need to keep a close eye on the I-25 corridor, the Pine Ridge, and the higher hills around Scottsbluff and Banner county for potential extensions this morning. Thankfully, even if snowfall rates become an issue, snow will struggle to stick on the pavement shortly after sunrise.

Snow will be ongoing as we head into this afternoon, although with the high May sun angle impacts should be limited with melting on area roadways. Snowfall rates will begin to ease down during the middle of the afternoon as the best dynamic forcing shifts east into the high plains. Some rain/snow mix expected down to 4500 to 5000 feet, but little in the way of accumulations since this will occur during the daytime hours. Remnant snow (or rain/snow mix below 5000 feet) will taper off and finally end by midnight tonight as the storm system transitions to an open wave trough and rapidly ejects northeast. Once all is said and done, this system should provide much needed moisture to the area with around a half inch of precip for the eastern plains, and close to 1.00 inch to as high as 1.50 inches for southeast Wyoming.

Main forecast concern after today will be how quickly we clear out at night. There is increasing confidence that a good part of the eastern plains with clear out by daybreak Tuesday with portions of Carbon county below 50% cloud cover as well. A hard freeze is expected late tonight through most of Tuesday morning, with freezing temperatures likely lasting until shortly before noon in portions of the forecast area. This is due to a record breaking unseasonably cold airmass behind the main storm system, which is forecast to settle over the area today. Current 10th to 25th percentile low temperatures tonight are between 14 to 20 degrees over most of the high valleys in southeast Wyoming, with 17 to 27 degrees across the eastern plains. Upgraded the Freeze Watch to a Freeze Warning for east central Wyoming and far northwestern Nebraska since these are the most likely zones to see clearing skies earlier in the night. Kept the Watch going for the remainder of the area, but mainly to see how this current storm system and potential snowfall pans out first. Conditions will improve a little on Tuesday with 700mb temperatures between -2c to -5c under northwest flow. High temperatures will be warmest where there is no snow pack...mainly over far eastern Wyoming and western Nebraska with highs in the 50s to low 60s. Further west, expect highs to generally be in the 40s and even upper 30s in areas with the deepest snow pack.

LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/

Issued at 230 PM MDT Sun May 17 2026

Certainly less active than the short term, but the long term period will still have some impacts. We will likely dip below freezing again on Tuesday night especially in regions that don't melt away all of their snow (i.e. areas west of the I-25 corridor). On Wednesday, temperatures will gradually moderate into the upper 50s to near 60 east of the Laramie Range and upper 40s to lower 50s west given weak isentropic ascent/warm advection as the longwave trough responsible for our anomalously cool weather dampens. There may be enough lingering moisture for a few showers and thunderstorms primarily over the higher terrain, however probabilities of seeing QPF > 0.05" are running at about 25%, so any moisture is unlikely to be beneficial. Given dry boundary layers as shown on model forecast soundings show a very dry boundary layer with surface dewpoint depressions exceeding 40 degrees, showers and thunderstorms will likely produce far more wind than rain.

Temperatures gradually warm on Thursday and Friday as a series of shortwave troughs embedded in quasi-zonal flow traverse across Eastern Wyoming and Western Nebraska, leaving in low (30%) chances for high-based showers and thunderstorms. Highs will gradually increase to climatological values (mid-upper 60s for Cheyenne to near 70 for the Nebraska Panhandle). Heading into the weekend, we will begin to dry out and encounter a faster warming trend to above- average temperatures as weak mid-level ridging establishes itself over the Rocky Mountain West, with no widespread or beneficial precipitation chances in sight.

AVIATION /18Z TAFS THROUGH 18Z TUESDAY/

Issued at 1146 AM MDT Mon May 18 2026

IFR to LIFR in place for the Wyoming terminals as visibilities remain under 3 miles and CIGS remain at or below 2 kft. For the Nebraska terminals, MVFR to IFR remain especially in the vicinity of any heavier showers. Expect CIGS to gradually increase after 06Z as this winter storm wraps up with the exception of KLAR and KRWL where low clouds are expected to remain in place through 12Z in addition to blowing snow at KRWL. 15-20 knot NE winds will remain in place through 00Z, gusting to 25-30 knots before backing to NW after 06Z. As surface high pressure settles into the region behind the ongoing system, winds will decrease to around 10 knots.

CYS WATCHES/WARNINGS/ADVISORIES

WY...Freeze Watch from late tonight through Tuesday morning for WYZ106-113-115>119. Freeze Warning from 8 PM this evening to 10 AM MDT Tuesday for WYZ101-102-107-108. Winter Weather Advisory until 6 PM MDT this evening for WYZ101- 105-106-111-115-117. Winter Storm Warning until 6 PM MDT this evening for WYZ103- 104-109-112-114-116. Freeze Watch from 9 PM MDT this evening through Tuesday morning for WYZ104-105-109>111. Blizzard Warning until 3 PM MDT this afternoon for WYZ110. NE...Freeze Watch from late tonight through Tuesday morning for NEZ002-003-020-021-054-055. Freeze Warning from 8 PM this evening to 10 AM MDT Tuesday for NEZ019-095-096.