textproduct: Cheyenne

KEY MESSAGES

- Above average temperatures and chances for gusty showers and some isolated storms through Sunday.

- A pattern change will bring a gradual cool down and increased chances for precipitation this week. Moderate to heavy rainfall possible Tuesday night through Wednesday night with some mountain snow expected.

SHORT TERM /THROUGH MONDAY NIGHT/

Issued at 225 AM MDT Sun Oct 11 2026

Current observations across the region show mostly cloudy to cloudy skies and periods of light rain along and west of the I-25 corridor early this morning. Rainfall hasn't amounted to too much thus far, even with a few thunder showers last evening. This activity is on the far eastern periphery of the potent Pacific storm system digging south across California and Oregon early this morning. This Pacific storm will allow the remnants of Tropical Storm Rachael to lift northward over Utah and Wyoming today bringing some much needed rainfall to those areas. Although we're expecting an increase in rainfall (and possible thunder) today, the main forcing will likely remain just west of the forecast area where flooding may become a problem in Utah and eastern Idaho. This system will also bring the first widespread snowfall to the northern Rocky Mountains today and Monday.

Expect similar conditions at the start of today compared to Saturday, with showers and thunderstorms gradually increasing in coverage from west to east across southeast Wyoming...mainly this evening and tonight. A little cooler this afternoon, mainly due to the increase in cloud cover and 700mb temperatures lowering a degree or two behind a midlevel cool front. PWATs are forecast to increase between 0.75 to 1.25 inches across the area, easily above the 95th percentile for this time of the year as the remnant tropical system lifts north. Also, models have trended much higher with winds over Carbon and Albany counties tonight with the GFS and NAM now showing 700mb winds between 50 to 60 knots. Believe this is the midlevel reflection of the remnant (sub)tropical storm quickly lifting north across central Wyoming tonight. This makes sense given the PWAT values will increase tonight above the 99th percentile and close to 00z to 12z maxes ahead of the subtropical low, based on NAEFS climatology for mid October. Issued a High Wind Watch for most of Carbon County and far western Albany county, including the Arlington/Elk Mountain wind prone area, late this afternoon through tonight. Gusts between 55 mph to 65 mph are possible with sustained winds around 30 to 35 mph. Models also indicate some strong lee-side subsidence near the Sierra Madre and Snowy Range, so will have to keep an eye on this. Convective winds will also be a concern along with very windy environmental winds during the late afternoon and evening hours. Continued to increase POP tonight up to 70 percent from Carbon county northeast to Converse and Niobrara county...with values gradually tapering down east of I-25. Multiple bands of showers and embedded thunder are expected...mainly between 3 PM today and midnight tonight. Remnant showers are possible early Monday morning, but should remain in the mountains and nearby valleys across Carbon County.

For Monday, pleasant most of the day with mild temperatures in the mid 60s to mid 70s across most of the region...perhaps around 80 for the central to southern Nebraska Panhandle. Models show a very subtle shortwave ridge axis building into the Front Range behind the subtropical remnant low...which is forecast to lift into the Dakotas and southern Canada. This break will be short-lived as all models indicate the Pacific storm system closing off from the mean flow and eventually tracking eastward across the Great Basin and Utah by late Monday night. Expect another increase in showers and thunderstorms. Convective parameters are marginal, so expect mainly rain showers (heavy at times) and embedded thunder. Cooler air continues to move into the region Monday night with low temperatures finally beginning to feel more like Fall (mid 30s to low 40s).

LONG TERM /TUESDAY THROUGH SATURDAY/

Issued at 119 AM MDT Sun Oct 11 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 /12Z TAFS THROUGH 12Z MONDAY/

Issued at 516 AM MDT Sun Oct 11 2026

Satellite and regional radar show widespread cloud coverage and light shower activity over southeastern Wyoming. A weak cold front is making its way south and should pass through the Nebraska Panhandle terminals and KCYS through mid morning. Expect a wind direction shift out of the north or northeast while winds remain light. Winds at KRWL will remain breezy, to at times strong, this afternoon. Some convectively enhanced wind gusts could approach or exceed 50 knots. Several rounds of showers and storms are possible throughout the day at mainly the southeastern Wyoming terminals. Starting tonight the remnants of Post-Tropical Cyclone Rachel will pass to the west and impart increased flow aloft over KRWL and KLAR. Especially during periods where near surface winds decrease, LLWS will occur. Up to 45-55 knots of shear are possible through Monday morning.

CYS WATCHES/WARNINGS/ADVISORIES

WY...High Wind Watch from 3 PM MDT this afternoon through late tonight for WYZ104-109>111. NE...None.