textproduct: Cheyenne

KEY MESSAGES

- Severe weather will be possible both Saturday and Sunday. SPC has issued a Slight Risk for the Southern Panhandle on Saturday 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 SUNDAY/

Issued at 335 AM MDT Sat May 16 2026

Active, with multiple hazards expected over the next 48 to 72 hours. Will handle the wintry portion of this storm in the Long Term discussion, and will mainly focus on thunderstorms and severe weather potential today and Sunday.

Current KCYS radar loop surprisingly showing a few isolated thunderstorm cells early this morning over the southern panhandle of Nebraska near Kimball and Sidney. Activity is pretty limited, but detected CG has been pretty consistent over the last few hours. This is likely due to the initial moisture surge/WAA above the surface across the eastern plains with Sidney's dewpoint increasing to near 40 degrees compared to the mid teens Friday evening. Also, a potent upper level jet is also present with good mid to upper level lift over the area and northeast Colorado. Jet dynamics are expected to play a role in convective activity today and Sunday across the area. Otherwise, not much going on for the rest of the forecast area with mostly cloudy skies and relatively mild temperatures for 300 am.

A marginal to slight risk of severe thunderstorms remains over most of southeast Wyoming (Marginal Risk) and western Nebraska, with the slight risk mainly for the southern Nebraska Panhandle today where the best moisture and forcing exist. Will have to keep a close eye on the moisture advection this afternoon as a frontal boundary is expected to develop across the eastern Wyoming high plains and slowly move east. Any additional low level forcing and convergence may result in additional coverage of strong to severe thunderstorms...and further west that previously expected. For now, expect moisture advection to be slow and take its time through the day. With limited moisture, strong to severe storms should be pretty isolated or widely scattered across the I-80 corridor and northward towards the North Platte River Valley. Mainly expect strong gusty winds, especially initially in the event, with plenty of DCAPE (1000-1900 J/KG) over the eastern high plains. As we head into this evening, boundary interactions and additional development may result in a secondary hail threat. There is an outside chance of a tornado or two, but this chance is mainly confined to the southern Nebraska Panhandle late this afternoon and this evening (2% to 4%) with some 0-3 km helicity, especially near boundary mergers. However, LCL's will be quite high during this event, so confidence will remain limited. Outside of the Slight Risk area, expect mainly strong gusty winds from thunderstorm outflow with all models showing inverted-V soundings for much of the afternoon, but can't rule out an isolated hail threat due to lower freezing levels. Scattered showers and isolated thunderstorms will linger through most of Saturday night with temperatures in the 40s and 50s.

For Sunday, chance for severe thunderstorms has lowered significantly with all models showing the initial cold front sliding through the area early in the day, considerably earlier than what was shown 24 hours ago. Limited CAPE behind the front with the best chance for strong to severe thunderstorms across the southern Nebraska Panhandle and far southeast Wyoming where the best instability and forcing will be located. The Slight Risk area has been shifted much further east, into central and eastern Nebraska. Will continue to monitor this into Sunday with some high res guidance shows some pretty strong thunderstorms on simulated prog radar reflectively. With additional cooler air moving into the area and good forcing, any thunderstorms may have small hail and gusty winds with several bands of thunderstorms expected. High temperatures on Sunday will be around 10 to 15 degrees cooler compared to Saturday as an extended rain/snow event is expected to begin Sunday evening. Please see Long Term discussion(s) for additional details.

LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/

Issued at 250 AM MDT Sat May 16 2026

Previous Long Term discussion is valid and on track, with a few updates/model changes compared to 12 to 24 hours ago:

1) Issued a Winter Storm Watch for most mountain zones (Laramie Range and Snowy Range), and included northern Carbon County and the Snowy Range Foothills, including I-80 between Laramie and Rawlins. Models have been very consistent in showing strong frontogenesis and lift in these areas. Although forecast snow accumulations are not quite at criteria, decided to handle the winter weather portion of this storm to take some pressure off the day shift, which will be dealing with severe weather, possibly both today and Sunday. Although this storm is late season snowfall, the timing of the heavy snow may be problematic since it mainly starts out moderate to heavy in the nighttime hours, where quick accumulations are more likely.

2) Quite a bit of uncertainty for the Laramie Valley since they hold onto a prevailing easterly wind for much of the event, and the axis of strong lift near the frontogenesis is mainly just west and north of the area. Although snowfall amounts were nudged slightly higher over a good chunk of the area, kept Laramie roughly the same (3 to 5 inches).

3) There is some uncertainty starting to creep into the forecast for the eastern plains. Several NAM solutions are showing a warm nose along and east of the I-25 corridor through much of the event. This may keep precip type mainly as rain along and east of the I-25 corridor. Will monitor this to see if it becomes a actual trend. Either way, plentiful moisture is expected but impacts will be very different. As for the GFS, 00z started showing a dry layer above 700mb creeping into the Laramie Valley and along the I-25 corridor out of the southwest. Again, will monitor this over the next 24 hours since this will result in some areas with somewhat lower precip amounts.

Previous LONG TERM discussion... Issued at 315 PM MDT Fri May 15 2026

Confidence is increasing in yet another significant, late season snow event impacting portions of the area Sunday night through Monday night. The overall synoptic setup will feature a double barrel upper level low diving in across the western CONUS this weekend. The main trough axis will be fairly slow moving, but a strong, secondary vort-max will swing across the base of the trough Sunday night into Monday, enhancing local forcing for ascent. Showery type precipitation Sunday afternoon will transition to a more stratiform precipitation by Monday morning. A reinforcing cold front is also expected to move southward into the area Sunday evening, leading to a surge in the northerly surface winds and steadily dropping temperatures. The mid-level cyclone will dive down into the interior Rockies during this period, which will close off between about 700 and 500-mb. This will allow moisture and wind to wrap in over the northeast side of the low, in a pseudo-TROWAL like setup, just on the wrong side of the system. Models are rather aggressive on strong isentropic lift and positive theta-e advection over much of the area Sunday evening and continuing through at least midday Monday. In addition, ensembles are in fairly good agreement showing strong frontogenesis setting up along the I-80 corridor west of Laramie. All together, we have numerous lifting mechanisms and ample moisture with nearly saturated vertical profiles.

Ensembles are pretty aggressive on liquid precipitation. Fortunately, this system looks to deliver beneficial moisture to a larger portion of the area, unlike the previous snow event this month which was mainly confined to Laramie, Cheyenne, and areas in between. The 25th percentile liquid precipitation exceeds 0.5" for the entire area, suggesting a good chance for widespread moisture. 50th percentile amounts exceed 1.0" over much of southeast Wyoming where the dynamics are a bit stronger and there will be more of a boost from orographic lift. This would ordinarily be great news for our drought stricken area, but unfortunately, this system will be very cold for this time of year. LREF mean 700-mb temperatures drop to around -4 to -7C over much of southeast Wyoming, and -2 to -5C over western Nebraska. A shallow cold air layer is also expected to undercut a deep warm nose aloft, but this warm nose is expected to remain largely below freezing. These temperatures will support accumulating snow down to about 5000 ft in elevation, and snowflakes mixing in with the rain for the entire area, even in the lower elevations of western Nebraska. Accumulations and impacts (due to snow) are less likely below 5000 ft. Rain will transition over to snow Sunday night in southeast Wyoming, so we may be able to get some snow sticking to the ground before the sun comes up. With the sun angle just a month away from the summer solstice, it will be very difficult to accumulate snow during the day, but we still should see some sticking to grassy/elevated surfaces. Most likely snow amounts are currently sitting around 4-7" in Rawlins and Arlington/Elk Mountain, 3-6" in Laramie, 2-4" in Cheyenne, Douglas, Saratoga, and Lusk, and a trace to 2" elsewhere. The mountains, particularly the Snowy Range, Laramie Range, and Muddy Gap area can expect higher amounts in the 6 to 12" range. While these are the most likely amounts, there is some concern for high end potential with this event. The strong signal for frontogenesis in Carbon county is particularly noteworthy. There is a plausible high end scenario where 10 to 16 inches falls in Carbon county, and 5 to 10 inches falls in other populated areas of southeast Wyoming. The current probability of this scenario is around 10 to 25%.

Deciduous trees are now fully leafed out across the area. With heavy, wet snow expected, the primary impact of this event is expected to be tree damage. Snow will have trouble sticking to the roads, but the higher elevations of I-80 in Carbon and Albany county may anticipate some road impacts. Unlike the previous snow event this month, this one will unfortunately be accompanied by significant surface winds. The high plains can expect a steady, cold north wind gusting around 25 to 35 mph. The surface high pushing up against the higher terrain and stalling will lead to an impressively strong reverse pressure gradient, which is likely to lead to strong winds in Carbon and Albany counties. There is high confidence gusts of 35 to 45 mph in this area, with the possibility of gusts approaching 55 mph. Blowing snow impacts will be reduced by the expected wet consistency of the snow, but we will need to keep an eye on this as well. There is some uncertainty concerning how these winds will affect snow accumulations on leafed out trees. On one hand, this could help knock snow off, but it also might increase the strain on branches and lead to more downed limbs.

The last impact of this event will be the expected cold temperatures. 700-mb temperatures are around the 2.5 percentile of climatology. With plentiful cloud cover, forecast high temperatures for Monday were nudged down towards the NBM 25th percentile, but this may even be still too warm. Highs will struggle to get above the mid 30s in southeast Wyoming where snow is falling, and even western Nebraska will get stuck in the low 40s. Monday night will bring the coldest temperatures of the event. Expect widespread freezing temperatures, with essentially the entire area expected to fall below freezing. Rawlins and Laramie are favored to drop below 25 degrees, with Cheyenne event maintaining a probability of around 40%. The main question will be cloud cover. If we can maintain some low cloud cover through the night, we may be spared the worst of the impacts of the freezing temperatures. However, early clearing will likely lead to widespread 20s and even some pockets of teens showing up. Record low maximum temperatures are likely during the day Monday, and record low minimum temperatures are likely by Tuesday morning. Those with sensitive vegetation or outdoor irrigation systems should take steps this weekend to prepare for the upcoming cold temperatures.

Behind this storm system, the warmup will be fairly slow as general troughing is expected to remain over the area through the week ahead. Expect temperatures to remain below seasonal averages through at least Wednesday, and possibly Thursday. The storm track will remain active as well with a continued stream of vort maxes moving through the area, which will keep slim chances for showers and a few thunderstorms going, but the potential for widespread rainfall will be fairly low after the main event concludes Monday afternoon.

AVIATION /06Z TAFS THROUGH 06Z SUNDAY/

Issued at 1122 PM MDT Fri May 15 2026

A relatively calm night along with VFR conditions will prevail across most terminals through the overnight hours. Things change Saturday morning as a system pushes into the CWA, increasing the threat of thunderstorms, some of which may be severe. Chances of thunderstorms will start off around KLAR at about 18Z, progressing east and north through the morning into the afternoon hours. All terminals, except KRWL, will have the possibility of thunderstorms by 22Z Saturday. In and around any thunderstorm that hits or comes near a terminal, expect gusty and erratic winds along with lower CIGS and reduced VIS in rain.

CYS WATCHES/WARNINGS/ADVISORIES

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