textproduct: Cheyenne

KEY MESSAGES

- Remaining warm Sunday with temperatures around 5 to 10 degrees above normal. There is a chance for showers and thunderstorms on Sunday as the next Pacific storm system moves onshore.

- A strong Pacific storm system will bring scattered showers and storms along with seasonably cool temperatures Monday through Wednesday. Slow warming trend expected later in the week.

SHORT TERM /THROUGH MONDAY/

Issued at 220 AM MDT Sun Sep 27 2026

Rather mild early this morning despite the dissipating cloud cover, with surface readings in the 50s to low 60s across most locations. Low level moisture is also higher than previously expected with dewpoints already in the 50s across portions of the western Nebraska panhandle. This should play a role in thunderstorm development today.

All models in pretty good agreement and show the main Pacific storm system moving onshore later today. This storm will quite a bit of energy, and some of that energy will transition eastward into the eastern Great Basin region and the Front Range as a potent upper level disturbance/vort max quickly lifts northeast across the area. Models show this disturbance entering the area late in the afternoon and through the evening hours, so convection may be delayed until this evening, or possibly late this evening. SPC has a Marginal Risk of strong to severe thunderstorms for today, but this appears to be a very conditional risk due to the timing of the disturbance and the time of the year. Model soundings are favorable east of the Interstate 25 corridor, with most locations near 800 to 1400 j/kg of MLCAPE and SBCAPE. 0-6km shear is marginal, but enough to consider some updraft rotation and tilting. However, soundings do show some decent CIN through most of the afternoon. Will continue to monitor the latest high res CAMs, but the HRRR, NAMNEST, and the RRFS are not showing anything other than some scattered rain showers over southeast Wyoming and western Nebraska through 900 pm. Another wildcard is the Low Level Jet, which is expected to peak around midnight across the high plains with forecast 700mb winds around 40 knots. There is concern that the upper level disturbance, if it continues to trend later in the day, will interact with the Low Level Jet, producing rare late-September nocturnal convection (likely strong). Again, high res CAMs aren't really showing this, but the previous 00z HRRR was hinting towards it across the central Panhandle. Will continue to keep an eye on this and brief the next shift, but unsure how aggressively to message this potential at this time. Kept POP between 20 to 40 percent across the area for mainly widely scattered to scattered coverage, with east central Wyoming and the northern Panhandle the most favorable area to receive some decent rainfall. Can't rule out a few stronger storms across the eastern plains...with the first chance this evening, and another chance later this evening once the low level jet increases.

For Monday, synoptic models continue to show good run-to-run consistency with the overall pattern, and more specifically, the Pacific storm system moving onshore across central California and then digging southeast into the desert southwest. Although PWATs are forecast to be between the 95th and the 99th percentile (0.75 to 1.25 inches) over the forecast area, there is little to no instability present due to ample cloud cover and cool-ish temperatures. The midlevels will still be relatively warm with poor lapse rates. The only notable forcing is from the 100kt jet max moving into Wyoming, Colorado and the Dakotas, with moderate to strong upper level diffluence present. Synoptic models continue to show limited precipitation. However, to complicate things: the last few runs of high res guidance are much more aggressive, showing large bands of moderate to locally heavy rainfall quickly lifting northeast across the area...more or less colocated with the best jet dynamics. This is where a bulk of the forecast uncertainty is present. High res CAMS also show some strong thunderstorm activity embedded in the large areas of moderate rainfall. Kept POP as is and increased them a bit across western Nebraska and the mountains of southeast Wyoming. A few of the higher peaks over 10,500 feet may see their first snowfall of the season. There is still some concern that this system may produce some excessive rainfall, but confidence is not very high. Daytime temperatures will lower into the 60s and low 70s. May need to adjust these temperatures even lower with the lack of sunshine and possibly some low clouds and fog for a good portion of the day.

LONG TERM /LATE MONDAY THROUGH SATURDAY/

Issued at 115 PM MDT Sat Sep 26 2026

Unsettled weather will continue into the early part of the week ahead, but it is widespread beneficial rainfall is looking less likely. A split trough approaches the area on Monday, with the northern split passing to our north, and the southern split will be abandoned over the southwest to eventually absorb abundant tropical moisture associated with the remnants of Hurricane Polo. While precipitable water will be well above average Monday through early Wednesday, pushing around the 90th to 99th percentile of climatology, forcing for ascent looks weak at best, and instability remains unimpressive. The official forecast maintains modest PoPs (mostly 20 to 50%) through Monday and into Tuesday morning, as we can expect to see at least a few showers and storms around, but odds of significant rainfall are slim. Probabilities for total precipitation (through Tuesday) over 0.1" are lowest between I-25 and the WY/NE state-line, running around 20 to 50% here. Western Nebraska and the higher terrain of southern Wyoming both have higher odds, between about 50 and 80%. That being said, expect rainfall to be spotty, though the abundant atmospheric moisture will support the potential for highly localized heavy rainfall. A cool front moving through the area will knock down temperatures for Monday, with Tuesday looking like the coolest day.

For the middle of the week, the most likely scenario puts our area just outside of the region of precipitation associated with a soggy closed upper level low to our south. Ensembles are still all over the place in terms of the location of this low pressure system as it ejects eastward into the plains Wednesday into Thursday, but only the far northern end of the envelope of solutions (10 to 20% probability) would bring any impact to our area. The vast majority of ensemble members keep all rainfall with this system to our south, but it is still worth a mention as a shift north would lead to a vastly different outcome than currently shown in the official forecast for Wednesday and Thursday. Expect temperatures to warm up through the latter half of the week, with highs peaking above seasonal averages on Friday.

Another low-confidence storm system is showing up in a handful of ensemble members around next weekend. This will be another Pacific trough moving from the northwest. In about 20% of ensembles, this system is strong enough to knock temperatures enough to support a widespread freeze Sunday morning along with a quick shot of rain and snow showers to the area. However, the other ~80% have light showers and a modest cool down, with overall minimal impacts.

AVIATION /12Z TAFS THROUGH 12Z MONDAY/

Issued at 550 AM MDT Sun Sep 27 2026

Strong Pacific storm system will begin to push onshore and gradually move into the Intermountain West over the next 24 to 36 hours. Expect increasing cloudiness over southeast Wyoming and Western Nebraska with a better chance of showers and a few thunderstorms.

HAZARDS/WEATHER TRENDS: VFR conditions will prevail at most terminals. Low coverage and uncertain timing of thunderstorms for today, and into late this evening, so will not add to most TAFs at this time. Short range ensembles are also showing a larger area of lower clouds over the Nebraska Panhandle, starting up north at first and then eventually building southward. This is kind of a surprise as the low level jet is expected to increase this evening through tonight, and IFR CIGS are typically unlikely in these cases. For now, added low-end MVFR CIGS to KCDR, but clouds to lift once the low level jet strengthens after 03z Monday. These lower clouds may sneak into KAIA and KSNY later on tonight.

CYS WATCHES/WARNINGS/ADVISORIES

WY...None. NE...None.