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.

SHORT TERM /THROUGH SUNDAY/

Issued at 315 PM MDT Fri May 15 2026

Active weather is progged to return for Saturday and Sunday as the next upper-level system starts to push towards the Intermountain West. Saturday afternoon and evening, much of the CWA will be placed broadly within the right entrance region of the upper-level jet, favoring continued synoptic ascent and favorable dynamics across the region. Multiple lobes of 500/700mb vorticity will eject out ahead of the incoming trough, further aiding in the overall synoptic ascent expected. Further down at 700mb, the associated low will slowly wrap up throughout the afternoon and evening hours, leading to stout, southerly to southwesterly flow for most locations east of the Laramie Range. Warm air advection increases after 12pm (noon, allowing for additional upward lift as the system pushes through. The surface low begins to develop Saturday afternoon over northeast Wyoming, inducing moist, southeasterly flow at the surface, especially across western Nebraska. A modest warm front will move northward, keeping the strong southeasterly funneling into the surface low. With the warm front ample surface forcing is expected, especially with the broader lift typically found within the warm sector of a mid-latitude cyclone. With strong southeasterly flow, dewpoints will surge into the mid-40s to low-50s across western Nebraska, with far southeastern Wyoming increasing into the mid-40s. Ample clearing is expected out ahead of the slowly advancing warm front, leading to a prolonged period of destabilization after sunrise Saturday morning. Hi-Res model guidance suggests around 1000 J/kg of MLCAPE with sufficient effective bulk shear, low-level turning, and minimal capping after about 20Z. However, the lower- levels look to remain fairly dry, increasing concerns for downburst potential. DCAPE values are around 1200 J/kg across western Nebraska, further increasing concern for a damaging wind potential on Saturday afternoon. Isolated supercell thunderstorms look possible on Saturday, but may grow upwards into a line fairly quickly due to nearly parallel bulk shear vectors to the expected warm front. Based on this information, discrete supercells could develop Saturday afternoon, but will likely grow upscale into a line a few hours after development. Forecast soundings suggest a potential for large hail, damaging wind gusts, and an isolated brief landspout cannot be ruled out due to low-level turning in the atmosphere. The Storm Prediction Center has highlighted much of the area in a Marginal Risk (Level 1 of 5), with portions of western Nebraska under a Slight Risk (Level 2 of 5) for severe weather Saturday afternoon. The main limiting factor for Saturday's severe threat will be the overall weaker forcing associated with a warm sector and the potential for strong capping until after 18Z or so. For Sunday, models show an upper level low over the Montana, Idaho, and northern Utah area. If the upper level low digs further south and is less progressive as it pushes into the Intermountain West, then southeast Wyoming may see a late season snow storm. If the upper level low is more progressive and moves further north, then less precipitation is expected, and in the form of mostly rain. For the 12Z, the deterministic models show the less progressive/further south solution of the southern low as it digs south near the four corners region late Sunday. The first of a series of cold fronts will push across Wyoming and eventually the high plains midday Sunday. At this time, it looks like the front will move through the area quickly, however some models do slow the front down and produce stronger convection from it. Low clouds and a strong capping inversion looks to be likely on the soundings east of Interstate 25 for most of the day. Therefore, pretty low confidence in this event so far. Severe thunderstorm wording was kept for mainly just the southern Nebraska panhandle again.

LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/

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 /00Z TAFS THROUGH 00Z SATURDAY/

Issued at 525 PM MDT Fri May 15 2026

VFR conditions will prevail across all terminals for the remainder of this afternoon through tonight with winds becoming 10 knots or less. A system will push into the region from the southwest, increasing the threat of thunderstorms. So, this activity will begin around 18Z for KLAR and gradually later for the terminals to the north and east. All sites, except KRWL, will have the possibility by 23Z Saturday. So, a PROB30 group was added to account for this. In any thunderstorm, especially if one comes near or goes over a terminal, expect gusty and erratic winds, lowering CIGs, and reduced VIS.

CYS WATCHES/WARNINGS/ADVISORIES

WY...None. NE...Red Flag Warning until 7 PM MDT this evening for NEZ434>437.