textproduct: Cheyenne

KEY MESSAGES

- Above average temperatures with scattered showers and isolated thunderstorm to start of the week. Some showers and thunder showers may contain gusty winds.

- Much cooler for the rest of the week with moderate to heavy rainfall possible across most of southeast Wyoming and western Nebraska Late Tuesday through early Thursday morning.

- First heavy mountain snow likely Tuesday and Wednesday as the Pacific storm system slowly move across the area. Significant accumulations possible above 8500 feet.

- First widespread freeze looking more likely late Wednesday night and/or Thursday night into Friday morning, ending the growing season.

SHORT TERM /THROUGH LATE TUESDAY/

Issued at 250 AM MDT Mon Oct 12 2026

High Wind Warning remains in effect for most of (lower) Carbon County, including the Elk Mountain/Arlington wind prone area extending eastward into far western Albany county early this morning. Winds have been gusting between 65 to 73 MPH consistently as the remnants of the tropical system, which impacted Arizona and southern Calif this past weekend, ejects northeast across western Wyoming. Warning will remain valid until 600 AM, and will then have to reevaluate if we need to extend the HW Warning through sunrise. This wind event is not like our other typical wind events and has been tricky to pin down due to different forcing mechanisms. Otherwise, added fog to the forecast for the northern and central Nebraska Panhandle with Chadron and Alliance reporting fog over the last few hours, expect these conditions to linger through sunrise before fog lifts later this morning.

Models have trended a little more dry today than previously expected, so lowered POP below 30 percent for most of the morning and early afternoon for Carbon and Albany counties. Kept POP below 10 percent further east as models continue to show a subtle shortwave ridge lifting northeast across the Front Range and Rocky Mountain region through the afternoon hours. Should be one more relatively pleasant day across the region before increasing cloudiness across the mountains and eastern plains late this afternoon and tonight. Relatively mild entering mid October with highs in the 60s north of I-80, and generally in the low to upper 70s from Laramie eastward to Alliance Nebraska and Sidney Nebraska. However, this break will be short-lived as all models indicate the Pacific storm system will become closed off from the mean flow aloft...and gradually tracking eastward across the Great Basin and Utah by late Monday night and early Tuesday morning. Expect another increase in showers and thunderstorms late this afternoon through tonight, and again Tuesday afternoon. Convective parameters are marginal, so expect mainly rain showers (heavy at times) and embedded thunder. Precipitation will come in bands initially (through early Tuesday), with a more solid coverage by the middle of the week as the Pacific storm system moves into the Rocky Mountain Region. Cooling trend will be more noticeable on Tuesday with highs struggling to reach the upper 50s and low 60s across the whole area as 700mb lower below +5c. Low temperatures early Tuesday will likely be in the 30s to low 40s across the area. Not expecting a freeze quite yet, but that's a definite possibility as we head into Wednesday and Thursday (please see Long Term Discussion for more info).

LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/

Issued at 111 AM MDT Mon Oct 12 2026

Our warm streak comes to a close Tuesday with cooler temperatures expected. The upper level shortwave passing north of our area ahead of the stalled upper level low will help push a cold front south. The cooler air is rather shallow and will have a hard time pushing past the Laramie Ranges. Locations along and east of I-25 should see about a 10 to 15 degree drop in afternoon temperatures compared to Monday, while further west a modest 5 degree drop is expected. The trends from yesterday are towards a more substantial cold front that stalls further south, thus pushing the axis of best theta-e advection southward into Colorado. This will be the favored corridor for heavier convective rainfall when the upper level system approaches. Scattered showers pass through the area through the day post front due to isentropic lift ahead of the upper level low. Not much rainfall from these showers, but a dreary and cloudy day can be expected.

Overnight, better forcing begins to move in with the upper level systems arrival. The best opportunity for beneficial rainfall occurs Tuesday night through Wednesday. Grand ensembles have the best chances of rainfall in the western and southern portion of the area where the mean precipitation totals are between half an inch and an inch. If we manage to pull off some MUCAPE on our side of the system, a few thunderstorms or convectively enhanced showers may materialize to give locally higher amounts. The snow level should also be low enough on the western half of the system to allow elevations at or above about 8500 feet to see precipitation cross over to snow. This would let the peaks of the Sierra Madre and Snowy Ranges see snowfall. It is a little soon to talk about possible ranges of snowfall at the peaks given the wide envelope of amounts in ensembles currently.

After Wednesday we still have uncertainty in the evolution of the forecast. As mentioned in the previous few discussions the uncertainty lies in if the upper level system is picked up by a southeastward advancing clipper out of Canada. The consensus starting to resolve in different models and ensembles are towards the solution that the trough ejection that becomes the clipper occurs near Alaska and moves southeast. Still, there are a few models such as the ECMWF that keep the ridge to the north strong enough to block the clipper and instead the upper level system stalls and lingers over our area while decaying through the forecast period. This would keep temperatures more mild and give better chances of rainfall, but does appear to be the outlier solution in more recent model cycles. If we commit to the GFS, and a majority of ensemble solutions at this point, of the system being picked up by the clipper then we can expect a cold end to the forecast. As the upper level system departs the cold air behind it will be forced southeast by a strong ridge. Gusty winds may accompany the cold air over the plains regions. Friday morning looks particularly chilly with perhaps the first widespread freeze of the season for a good portion of the area. Currently the likelihood of freezing temperatures from the Grand Ensemble for areas along and east of I- 25 are 20-40%, while west have a 50-80% chance. It is important to mention that a good number of the GEFS ensemble members are more aggressive with the progression of the trough that promotes these cold temperatures and are skewing the outcome of the Grand Ensemble towards the colder solutions. If we get a solution somewhere in the middle we could have a portion of the upper level trough elongate and stretch southwest while the majority gets swept up. A small chance this solution allows some upslope flow with the remaining moisture to create snow showers. Snow levels with be fairly low at around 6-5000 feet. Saturday morning looks also chilly as the western edge of the cold air mass lingers over the Panhandle. After the cold spell we warm up in the return flow post front Saturday and Sunday afternoons.

AVIATION /06Z TAFS THROUGH 06Z TUESDAY/

Issued at 1106 PM MDT Sun Oct 11 2026

Winds have decreased at most terminals tonight, other than KLAR and KRWL. Winds will remain light and variable for the terminals with winds increasing into the afternoon hours. KLAR and KRWL will remain gusty throughout the night and for much of the day tomorrow. Low clouds started to move into KCDR tonight with low ceilings expected to continue for the next several hours. KAIA may also see decreasing ceilings after 11Z when upper-level clouds clear out. IFR ceilings will be possible. All ceilings improve after 15Z in the morning.

CYS WATCHES/WARNINGS/ADVISORIES

WY...High Wind Warning until 6 AM MDT early this morning for WYZ104- 109>111. NE...None.