textproduct: Cheyenne

KEY MESSAGES

- Chilly temperatures will continue for the next several days. Another round of freezing temperatures expected this morning in areas with snow cover, with patchy frost and fog elsewhere.

- Isolated to scattered showers and a few thunderstorms will continue through Wednesday night. A more widespread round of showers and thunderstorms expected Thursday into Friday.

- Slightly above average temperatures and pleasant weather expected for the weekend.

SHORT TERM /THROUGH THURSDAY NIGHT/

Issued at 215 AM MDT Wed May 20 2026

Current KCYS radar loop shows some light rain showers with a little bit of snow above 7500 feet across the far southeast Wyoming near Cheyenne and Pine Bluffs and the southern Nebraska Panhandle early this morning. The upper level trough axis near the Utah border and WAA aloft out ahead of it is responsible for this activity. Periods of light rain showers will likely continue this morning and into the early afternoon hours with breaks at times. Watching some fog across the I-80 Summit also and will likely need a Dense Fog Advisory shortly since the precipitation appears to have shifted to the east. Southeast winds should continue for the next 6 hours over the Summit, so do not expect the fog to lift until midmorning. Otherwise, Freeze Warnings and Frost Advisories continue for most of southeast Wyoming and Sioux County over western Nebraska.

Slow warming trend will continue for today and Thursday as a long wave trough settles into the western third of the United States. Carbon county will rebound today with highs in the upper 40s to middle 50s with recent webcams showing rapid snow melt. There are still areas with deep snow pack, and those locations will likely still make it into the middle 40s. Kept 20 to 40 percent POP for this afternoon with some weak WAA aloft continuing through the day but better instability should keep widely scattered rain showers and isolated thunder going through this evening. Not as cold tonight with lows in the 30s to low 40s across most of the high plains, and upper 20s to low 30s for Carbon and Albany counties.

Later on Thursday, models show a potent clipper system digging south out of Alberta Canada and slowing down over the region. Will have to monitor this system for additional mountain snowfall, but expect most of the lower elevations to stay as rainfall. The system has trended a little colder compared to yesterday, with rain/snow mix down to 6500 feet...but any accumulations should be minimal for Laramie and Rawlins with generally no impacts on area roadways. Good low to midlevel forcing with this system, and daytime instability will aid in shower and thunderstorm development with CAPE values between 400 to 800 j/kg. Could see some decent rainfall amounts into Friday, with 25th to 50th percentile QPF amounts between a quarter inch and half inch. Some places across western Nebraska could even see up to 1 inch of rainfall from this system depending on the coverage of deep convection. Increased POP above 75 percent for most of the area with the good chance for another much-needed wetting rainfall.

LONG TERM /FRIDAY THROUGH TUESDAY/

Issued at 139 AM MDT Wed May 20 2026

An active and summer-like weather pattern is expected to take shape Friday through most of next week. Upper-level trough continued Friday and Saturday before zonal flow returns for Sunday and Monday. The next best chance for upper-level troughing looks to be Tuesday through the end of the week as a deep, upper-level trough near the West Coast pushes eastwards through mid-week. The 500mb flow will feature a very similar progression throughout the next several days, but isolated vorticity lobes will pass across the CWA, leading to increasing synoptic ascent despite the largely zonal upper-level flow and large-scale ridging late in the week. Westerly to southwesterly flow will dominate at 700mb Friday through much of the upcoming week, with moisture continuing to advect in with the 700mb from the Pacific Ocean just southwest of southern California. Despite the influx of moisture, the NAEFS Mean suggests that Precipitable Water values will remain seasonal for this time of year, so significant rainfall is not expected at this time though still likely more than the region has seen throughout much of this "winter" season. Looking at 700mb temperatures, a warming trend is expected Friday through much of the week, with 700mb temperatures over 10C returning for much of the region early next week. Surface temperatures will also see a warming trend through the weekend and into next week, with a small potential for slightly warmer than average temperatures, favored by the NAEFS Mean 700mb Temperatures being in the 90th percentile for isolated portions of the CWA.

While every day in the longer term forecast will feature some chance for isolated, afternoon showers and storms, as is quite typical with a summer-like pattern, Friday looks to be the most active day with the best potential for isolated, strong to severe thunderstorms. The next best day for precipitation will be Wednesday as the next upper- level trough is progged to push into the region. Looking at Friday, a messy, 700mb low will slowly get its act together in the morning hours becoming a closed low by late morning. An attendant surface low will push northeast out of northeastern Colorado, placing the CWA on the cooler side of the system as a whole. However, 700mb warm air advection is expected to start by the early afternoon hours as warmer temperatures further south start to push north as the first upper-level short-wave trough move off to the northeast and the second slowly swings across the Intermountain West for the overnight hours. Therefore, during the day, there will be favorable ascent in the form of 500mb vorticity maxima moving across the region combined with 700mb WAA, residual ascent associated with the surface low, then finally a secondary, weaker cold front as the second short-wave pushes through the region overnight Friday into early Saturday morning. Hires guidance does not quite reach Friday afternoon and evening at this time, but the NAM suggests anywhere from 200 to 700 J/kg of MUCAPE across the western Nebraska Panhandle. This would be enough, combined with the synoptic ascent across the region, to get at least a few rumbles of thunder, but also the possibility of very gusty winds and possibly some isolated hail. It will be interesting to see how hires guidance depicts this system as it gets into the time range, especially since forecast NAM soundings suggest a very wet environment with very strong 0 to 3km shear.

AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/

Issued at 1140 MDT Tue May 19 2026

Lighter winds, generally less than 10 knots, will continue for the overnight hours across all terminals. In addition, precipitation chances will increase over the next several hours at KCYS and then spread eastward into the Nebraska Panhandle between 12 and 15Z, with KAIA and KSNY having the best chances. This precipitation will bring in lower CIGs and reduced VIS, which could make flight categories dip down to MVFR and/or IFR conditions. Winds will ramp up again, starting around 12Z across southeast Wyoming and between 15 and 18Z for the Nebraska sites. So, expect gusty southerly winds increasing to 20-30 knots. With the added moisture that we've seen across southeast Wyoming over the past day or so, BR/FG once again may be possible, greatest chance at KRWL and KCYS tonight.

CYS WATCHES/WARNINGS/ADVISORIES

WY...Frost Advisory until 8 AM MDT this morning for WYZ102-106-107- 117. Freeze Warning until 8 AM MDT this morning for WYZ101-115. Freeze Warning until 10 AM MDT this morning for WYZ104-105- 109>111-113-116. Dense Fog Advisory until 9 AM MDT this morning for WYZ116

NE...Frost Advisory until 8 AM MDT this morning for NEZ095.