textproduct: Cheyenne

KEY MESSAGES

- A significant, late season snow storm is moving across the area. The greatest impacts are between Tuesday afternoon and Wednesday morning.

- Snow will accumulate over 5500 feet in elevation, with significant snowfall expected in and near the Snowy Range and southern Laramie Range

- Snowfall is expected to be heavy and wet, which could damage tree limbs and produce power outages.

- Travel impacts due to snowfall are expected along Interstate 80 between Rawlins and Cheyenne, and Interstate 25 between Wheatland and the Colorado state line.

- Impacts may extend eastward on Interstate 80 towards Kimball, mainly Tuesday afternoon and Tuesday night as colder air moves into the area.

- Drier, warmer, and windier weather returns to the area for the second half of the work week.

SHORT TERM /THROUGH WEDNESDAY/

Issued at 400 AM MDT Tue May 5 2026

The significant, late season snow event is underway across the area this morning. Overall, the forecast remains largely on track with relatively minor adjustments made to the official forecast with the latest update. Current GOES water vapor imagery shows the synoptic features in place to set up active weather over the next few days. The broad, closed upper level low over the West Coast is meandering inland this morning, with abundant Pacific moisture stretched out from northern California towards our area. Meanwhile, the northern branch shortwave is apparent over central Montana this morning, which will be bringing a reinforcing shot of cold air and forcing for lift sometime this afternoon. The latest mesoanalysis shows potent frontogenesis parked more or less right along the I-80 corridor this morning. Overrunning isentropic lift is primarily over northern Colorado but extends just across the state line and into the I-80 corridor. These two forcing modes are driving widespread precipitation, mainly over the southern half of the forecast area. Laramie is the winner so far, picking up 0.23" liquid as rain last evening, and another 0.27" as snow as of 3AM. The current phase of the system is expected to last through around sunrise or perhaps a few hours later. After that, models show the strongest frontogenesis slipping to our south. Isentropic lift will keep scattered precipitation going through the morning hours, but we should see rates ease while coverage on radar becomes a little spottier. Plentiful cloud cover will keep unseasonably cold temperatures over the area today. Laramie, Cheyenne, and possibly Rawlins will probably hover within a few degrees of freezing all day, while others will only make it to the 40s at best. Chadron will be the warmest spot, as the area is unfortunately expected to miss out on this event.

The second phase of the event will kick up this afternoon as the reinforcing shortwave trough mentioned above pushes southward. Look for increasing isentropic lift, followed by another surge in frontogenesis later as the upper level low strengthens and begins to absorb the Pacific closed low. This feature will also bring an additional surge of cold air through the area, which should cause snow levels to drop again this afternoon and evening. More cold air and stronger forcing will thus increase the coverage of snow impacts across the area. Due to this, the Winter Weather Advisory was expected to include central and northern Carbon County beginning at 6PM, and eastern Laramie and Kimball counties beginning at 3PM. Laramie remains an area of greater uncertainty. So far, the low- level easterly downslope flow appears to have been easily cancelled by the synoptic forcing. Current thinking is that the downslope flow will dominate later in the event when we lose the powerful frontogenesis. However, current forecast snow totals are pretty close to Warning criteria for the city, so we will need to watch this closely for an upgrade to a Winter Storm Warning if needed.

Concerning total liquid and snow amounts, the forecast has changed little since yesterday. The official forecast incorporates a blend of HREF and ECMWF ensemble guidance for QPF, and ends up a little below the NBM which still looks a little on the aggressive side. The most likely amounts are currently around 8" in Cheyenne, 5" in Laramie, 3" in Kimball, and 3" in Rawlins. The higher elevations of I-80 around Arlington and the Vedauwoo area still look like the bullseye of this system, with 10 to 18" expected. It would not be a surprise to see some amounts locally over 2 feet show up in the Snowy Range, the southern Laramie Range, or their adjacent foothills. We have seen the 10th and 90th percentiles closing the gap a little bit over the last 24 hours as confidence improves, but there is still a fairly wide range of outcomes, which will largely depend on how long we can keep strong frontogenesis in place in our area. In terms of impacts, travel conditions could improve a little during the day today with the benefit of the strong early May sun, but expect this to deteriorate in the late afternoon or evening again as temperatures cool again. The heavy wet snow accumulation on trees remains a primary concern with this event. As trees are largely leafed out or in the process of leafing out, trees will accumulate more snow than usual, which is already expected to be of a fairly dense quality. Therefore, damaged or downed trees and possibly powerlines will be a concern through Wednesday morning.

Model guidance differs in how long precipitation will last into Wednesday. The upper level low will dive nearly straight north to south, and recent guidance shows this system trying to close off as it absorbs the Pacific low pressure system. This could allow overrunning isentropic lift to continue through much of the day, although even in this case, rates should be fairly light by this time. With lower rates and the help of the high sun angle, conditions should improve Wednesday morning. All headlines continue through 9AM Wednesday, except the higher terrain which expire at 12PM Wednesday. Once the axis of the upper level shortwave trough finally passes through the area, much drier air and subsidence will move in overhead, but it is still unclear if that will be Wednesday morning, or as late as early Wednesday evening. Wednesday will be another chilly day regardless, but high should climb a few degrees above today's values. In addition to the snow, we will have a widespread freeze tonight, and this will locally be a hard freeze.

LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/

Issued at 400 AM MDT Tue May 5 2026

Drier air will move in overhead Wednesday night, leading to clearing skies. Areas with fresh snow cover (primarily Laramie and Cheyenne) may have a window to see temperatures drop quickly before westerly winds and strong warm air advection returns late Wednesday night or Thursday morning. We could see overnight lows reached in the evening, with warming occurring later as the winds pick up. The arctic high pressure moving through over the next few days will be settled in over the interior Rockies by Wednesday night. On the large scale, the overall weather pattern will shift into a northwest flow pattern with a ridge located over the West Coast, and the persistent upper level trough remaining over the Hudson Bay region. Another progressive shortwave will approach the area as early as Thursday. This feature will be accompanied by a surface trough, which will drop surface pressure over the High Plains. As a result, we will need to watch for the potential for a gap wind event Wednesday night into Thursday morning. High wind probabilities remain around 30 to 40%. Interestingly, this event appears to a low- level / surface driven gap wind event, which is somewhat unusual this late in the wind season. 700-mb winds look unlikely to exceed 50 knots, and 700-mb height gradients are fairly unimpressive. For now, winds were nudged towards the NBM 90th percentile in the official forecast, but remain below high wind criteria. Both the Arlington/Elk Mountain and I-80 summit areas will have ample snow on the ground when the winds pick up. We could have some blowing snow concerns, but there is a lot of uncertainty in this owing to the snow consistency and how much thawing (i.e. wetting the snow) can occur on Wednesday.

Expect a breezy to windy day elsewhere Thursday with temperatures quickly recovering to near seasonal averages. The Laramie to Cheyenne corridor will remain cool, but the rest of the area should warm above average. The next shortwave aloft will arrive late Thursday, and will bring a chance scattered showers and isolated thunderstorms across the area Thursday afternoon and Thursday night. This will not bring much rainfall, but temperatures will be warm enough that we will not have to worry about snow. The northwest flow pattern should remain fairly locked in place through the weekend. Overall, expect temperatures near seasonal averages and breezy to windy northwest winds every day. We will also remain fairly unsettled, with chances for showers each day.

AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/

Issued at 1152 AM MDT Tue May 5 2026

A series of weather disturbances with plentiful low and mid level moisture will move across the terminals this afternoon and especially tonight, producing enough lift for widespread snow, and low ceilings and visibilities, south of a Rawlins to Scottsbluff line.

Wyoming TAFS...High confidence in widespread IFR due to moderate to heavy snow, with periods of fog as well. Ceilings and visibilities will improve after 09Z at Rawlins to MVFR with VFR after 12Z. Laramie and Cheyenne will have IFR conditions in light to moderate snow, and fog, until early morning, around 14Z, then improve to MVFR Wednesday morning.

Nebraska TAFS...IFR continues at Sidney through much of the period, in light snow and fog, due to ceilings and visibilities, with VFR flight rules developing after 14Z Wednesday.

Scottsbluff, with moderate confidence, will see occasional MVFR in rain and snow through this evening, with visibility obstructions around 2 miles at times. VFR flight rules return after 10Z with ceilings improving and no visibility restrictions.

High confidence in Chadron and Alliance seeing occasional MVFR through late afternoon, due to visibility and ceilings at Chadron, and ceilings at Alliance, with VFR and ceilings improving this evening and late tonight.

CYS WATCHES/WARNINGS/ADVISORIES

WY...Winter Weather Advisory from 3 PM this afternoon to 9 AM MDT Wednesday for WYZ119. Winter Weather Advisory until 9 AM MDT Wednesday for WYZ103- 105-106-115. Winter Weather Advisory from 6 PM this evening to 9 AM MDT Wednesday for WYZ104-109. Winter Storm Warning until noon MDT Wednesday for WYZ110-114- 116-117. Winter Weather Advisory until 9 AM MDT Wednesday for WYZ112. Winter Storm Warning until 9 AM MDT Wednesday for WYZ118. NE...Winter Weather Advisory from 3 PM this afternoon to 9 AM MDT Wednesday for NEZ054.