textproduct: Cheyenne

KEY MESSAGES

- Severe weather will be possible both Saturday and Sunday. A slight risk is in effect this afternoon for the Nebraska Panhandle, with a marginal risk for Sunday.

- 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 average by Thursday.

SHORT TERM /THROUGH MONDAY NIGHT/

Issued at 216 PM MDT Sat May 16 2026

Radar echoes are seen across the area this afternoon with stronger storm activity currently just south and east of the CWA. Current mesoanalysis shows some weak to modest MUCAPE across the region, ranging from 250-600 J/kg, strongest in the southern Nebraska Panhandle. Bulk shear is looking a bit more favorable with around 35-40 knots for our eastern zones, and 100 m2/s2 of helicity with a bullseye of 200 just south of Sidney. High resolution guidance has been in pretty solid agreement on the overall setup today with the ongoing precipitation and expectation that storms will begin to consolidate in extreme eastern Wyoming/northern Colorado, and form into a strong line as they reach the eastern periphery of our CWA in the Nebraska Panhandle. Current timing for this would be between 22-02Z, with the bulk of the activity exiting the CWA after that time. This looks to favor the strongest activity from about Scottsbluff southeastwards during that timeframe, with large hail initially followed by strong winds quickly thereafter as the primary hazards, along with a low-end tornado risk most likely along the I-80 corridor in the Panhandle. That being said, models were keeping activity fairly quiet until that time for our Nebraska Panhandle zones, but some decent thunderstorms have formed just south and east of Sidney, which could help to limit severe potential for this area. Still, would expect that the atmosphere would be able to recover and produce another round of stronger storms into the later afternoon and evening even at Sidney. Elsewhere across the CWA, expectation of strong to severe wind gusts possible with inverted V soundings present promoting some downdraft activity this afternoon and evening.

Overnight scattered showers and weak thunderstorms should persist with another round of strong to severe thunderstorms possible on Sunday. This time the front is expected to be through the region, limiting overall severe potential as temperatures will be around ten degrees cooler tomorrow with much more limited instability. Still, some lingering severe parameters should be present once again across our southeastern zones, so a few strong to near severe storms may be possible during the day with multiple rounds of activity, with small hail and gusty winds possible.

Now behind the cold front Sunday evening, look for temperatures to plummet as a surge of cold Canadian air descends as the stout upper low dives across the Four Corners and then swings up into Nebraska by Tuesday morning. This will promote some aggressive forcing and with modest moisture present, we'll see rain continuing across the area with elevations generally above 5000 feet transitioning to snowfall Sunday evening and continuing into Monday. For this update, have added the Rawlins area into the Winter Storm Watch as we're looking at the potential for 6+ inches of fresh, heavy wet snow. The one caveat to locations outside of the mountains will be the fact that temperatures have been warm, and with how late season this system is, snow ratios of around 7-10:1 are expected, keeping us from seeing notably heavier snowfall. That being said, with heavy wet snow we do have to worry about trees and power lines suffering from the weight of this activity and causing local damage and power outages. And if snow falls quickly, it can accumulate on roads enough to shut down travel before melting off. High resolution guidance has dialed back accumulations further east into Cheyenne proper though, so for this update did reduce us back to around an inch. And once again with how warm temperatures have been, it's going to be tough to make accumulations stick even on elevated surfaces or grasses east of the mountains, but we will definitely feel the cold at the bare minimum. Temperatures will struggle to eclipse the mid 30's to mid 40's on Monday, and lows will bottom out overnight into Tuesday morning below freezing across our entire CWA, nearing record cold. Any sensitive plants and crops will surely be impacted by this system, and the appropriate precautions should be taken accordingly.

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 /06Z TAFS THROUGH 06Z MONDAY/

Issued at 1205 AM MDT Sun May 17 2026

Active. 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 in the afternoon. Low clouds are also expected once these winds become more northeasterly this afternoon and tonight over the high plains. Rain will gradually change to snow late in the TAF period for KRWL, KLAR, and after 06z for KCYS.

HAZARDS/WEATHER TRENDS: Low confidence forecast for any MVFR or even IFR conditions between now and 00z Monday due to typical timing and coverage concerns with convection, in addition to intensity of precipitation. Handled most likely timing with PROB30 groups and will wait to see what develops before changing these to TEMPO or prevailing. Otherwise, expect VFR conditions to prevail with KCDR, KAIA, and KSNY the most likely terminals to see low CIGS by 12z.

CYS WATCHES/WARNINGS/ADVISORIES

WY...Winter Storm Watch from Sunday evening through Monday afternoon for WYZ103-104-110-114-116. Winter Storm Watch from late Sunday night through Monday afternoon for WYZ109. NE...None.