textproduct: Cheyenne

KEY MESSAGES

- Red Flag Warnings continue for the Nebraska panhandle through 7 PM Friday evening.

- Next chance for precipitation returns during the weekend alongside cooler conditions. Severe weather will be possible both Saturday and Sunday.

- There is a Marginal Risk (Level 1 of 5) for severe weather Saturday with a Slight Risk (Level 2 of 5) for severe weather on Sunday.

- A potential late season snowfall event is taking shape to start the work week. Colder than normal temperatures may linger into the middle of the week.

SHORT TERM /THROUGH SATURDAY NIGHT/

Issued at 204 AM MDT Fri May 15 2026

Another warm and dry day is in store for southeast Wyoming and western Nebraska as afternoon temperatures warm into the low-70s to mid-80s and humidity values drop into the single digits once again. Largely zonal flow aloft will keep precipitation chances at bay, while westerly 700mb flow increases downslope warming and drying along and east of the Laramie Range. A subtle increase in 700mb winds through the afternoon hours will enable breezy conditions near the surface, leading to favorable conditions for rapid fire starts and spread. Red Flag Warnings remain in effect through 7 PM this evening due to the dry, crispy, and breezy conditions anticipated across the region. Clear skies turn cloudy this evening as a subtle, 700mb shortwave pushes across the region. No precipitation is expected today.

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 500mb 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. Modest warm air advection kicks up after noon, allow additional upward lift to aid the system as a whole. 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 in and around the region, ample surface forcing is expected, especially with the broader lift typically found within the warm sector of a midlatitude 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. Hires model guidance suggests 800 to 1000 J/kg of MLCAPE with forecast RAP soundings suggesting ample effective bulk shear, low-level turning, and minimal caping 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 tornado 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 caping until after 18Z or so.

LONG TERM /SUNDAY THROUGH THURSDAY/

Issued at 204 AM MDT Fri May 15 2026

Active in the long range, with models coming into better agreement with a potential late season snow event for most of southeast Wyoming and possibly the higher elevations of western Nebraska. However, considerable uncertainty exists regarding a potential severe weather event for the high plains Sunday afternoon and travel impacts on Monday.

At the end of the weekend, models show a double-barrel upper level low pressure system over Montana, Idaho, and northern Utah. The evolution of this system will be key in determining which end of the spectrum our sensible weather will be. If the southern upper level low/trough digs further south and is less progressive, southeast Wyoming may see a late season snow storm. If the southern upper level trough/low is more progressive and further north, less precipitation is expected, but in the form of mainly rain. For 00z, all 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. Will have to monitor this area closely for severe thunderstorms over the next few days. At this time, it looks like the front will move through the area a little too quick for much of a severe threat. In addition, low clouds and a strong cap inversion are present on both the GFS and NAM soundings east of Interstate 25 for most of the day. Therefore, pretty low confidence in this event so far (~10%), but will continue to keep an eye on it as we head into the weekend. Kept severe thunderstorm wording for mainly just the southern Nebraska panhandle for now.

Things get interesting Sunday night and Monday with cyclogenesis over the central and southern plains and an intense polar surface high behind the main cold front. Models show a strong surface pressure gradient with upslope north to northeast winds, plentiful moisture, and decent lift/dynamics. Forcing will be mainly be from low level upslope flow/convergence and upper level jet dynamics, but there is some hints of instability as well with a period of ample frontogenesis Sunday night into early Monday. Will need to watch this evolution closely with all models showing around an inch of QPF. Ensemble means are even higher, closer to 1.5 inches of QPF...especially along the I-80 corridor and over towards western Nebraska. All models show 700mb temperatures plummeting below -5c and close to -10c by noon Monday. This places the snowlevel around 5000 feet, with some snow flakes down to elevations as low as 4500 feet. Of course, lots of uncertainty with a system like this in the middle of May, similar to the heavy snow event on May 5th, where the grassy and elevated surfaces saw decent snow accumulations but little accumulated on the pavement. For this forecast, will trend towards climatology and prior May late-season snow events. Expect most of the accumulation below 8000 feet to remain on grassy/elevated surfaces. However, if models start showing the snowfall occurring more in the nighttime hours, may need to reevaluate and adjust.

In addition, temperatures will be quite cold with highs on Monday struggling to reach 40 degrees. When/if widespread precipitation is falling, these highs may be optimistic. Low temperatures Monday night and early Tuesday morning may be down right frigid for this time of the year, especially if we maintain a snow pack with clearing skies overnight. At this time, the base NBM has lows in the upper teens to upper 20s across most of the area. NBM 10th percentile and grand ensemble 10th to 25th percentile are well into the teens to low 20s across the region, even western Nebraska. These lows may shatter some long standing low temperatures for mid-late May (1910s to 1960s). For the rest of next week, all models and ensembles show a slow warming trend as the storm system lifts northeast into the Great Lakes region. Long wave upper level trough will remain over most of the western US, but weaken over time as a shortwave ridge axis moves into the west coast. Northwest flow will continue over Wyoming, with 700mb temperatures maybe climbing above 0c by Wednesday night. Cloudy and cool conditions are expected with several embedded shortwave/vort maxes meandering across the area, resulting in showers and possibly some thunderstorms each day.

AVIATION /12Z TAFS THROUGH 12Z SATURDAY/

Issued at 545 AM MDT Fri May 15 2026

Dry westerly flow will continue over the next 24 hours with some midlevel cloudiness developing later in the day. Typical diurnal winds are expected with gusty west to northwest winds between 15z Friday to 02z Saturday.

HAZARDS/WEATHER TRENDS: VFR will continue into early Saturday morning with some SCT-BKN midlevel cloudiness at all terminals late in the afternoon. Westerly winds will occasionally gust up to 35 knots at KRWL and KLAR after 15z, with gusts up to 25 knots elsewhere.

CYS WATCHES/WARNINGS/ADVISORIES

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