textproduct: Cheyenne

KEY MESSAGES

- Cooler temperatures will prevail for the rest of the week with increasing confidence is widespread rainfall Tuesday evening through Thursday morning.

- Accumulating snow is likely above 8500 ft in elevation Tuesday evening through Thursday morning.

- Near freezing temperatures are possible (20 to 40% chance east of I-25) Wednesday night. A growing season-ending freeze is increasingly likely Thursday night into Friday morning across the entire area.

SHORT TERM /THROUGH WEDNESDAY/

Issued at 349 AM MDT Tue Oct 13 2026

Areas of showers are moving northeast from Laramie through Glendo and Lusk. Fog is also being observed along the Laramie foothills, with patchy areas eastward along I-80 near Kimball and Sidney. This is showing up nicely on the night fog and microphysics GOES products. Other locations east of I-25 are otherwise under a low cloud deck that may lower enough to produce areas of fog through the morning. A subtle mid level shortwave associated with the current shower activity will continue to move northeast out of the area through the morning. Behind it sinking air will dampen more widespread rain potential through the majority of the morning and early afternoon and reduce cloud coverage. This reduced cloud coverage may allow afternoon high temperatures to reach a few degrees above the forecast for portions of the southern Nebraska Panhandle. Otherwise, highs are expected to be in the high 50s to low 60s for most locations outside of the ranges.

Towards evening an increase in deep layer moisture and synoptic lift on the advancing eastern flank of the upper level low will start to increase cloud coverage and precipitation from southwest to northeast. PWATs are elevated at between 0.5 and 0.75", with basically the entire area in the 90th to 95th percentile for this time of year. In other words, showers will be rather efficient rainfall producers, particularly if more convectively enhanced bands develop. High resolution models are depicting areas in the intermountain basins and along the Laramie Ranges receiving QPFs of between 0.75 and 1 inch through Wednesday morning. The upper ends of these predictions are upwards of 2 inches. Not impossible at locations where training convection occur. In addition to the widespread rain is snow at mountain peaks. The snow levels are anticipated to drop below 10 kft around sunset tomorrow allowing precipitation to transition into snow at our higher elevations. These levels should drop gradually throughout Wednesday to 9 or 8 kft. The northeasterly flow should be optimal for snowfall on the north and east face of the Snowy Ranges where totals for the first half of this event are forecasted to reach around 8 inches. There is a 20-30% chance that totals reach 12". Winter weather advisories may be necessary in the future for the Snowy Mountain zones if trends hold. Other summits looks to also receive a few inches of snow, though as mentioned the flow is not as ideal or moisture misplaced for higher amounts. Overnight lows generally in the low 40s to mid 30s can be expected with areas of fog over the Nebraska Panhandle.

A wet and dreary day is shaping up for Wednesday as the upper level low advances into the CWA. Multiple rounds of showers and isolated thunderstorms can be expected throughout the day. The HREF and SPC REFS are in good agreement that the focus of this rain will be along the northern and eastern foothills of the Laramie Range where upslope flow is the greatest. A local maximum of 2 inches of rain is supported by these high resolution ensemble model suites near Wheatland. Elevated winds near the low pressure center in Carbon and Albany Counties could be experienced. If the low pressure system is on the stronger envelope of solutions, wind gusts of 40 to 50 mph are possible. These winds would give wind chills 10 degrees below air temperature. Given the widespread shower and cloud coverage afternoon high temperatures are expected to peak in the mid 40s over much of our Wyoming areas and low to mid 50s over the Nebraska Panhandle.

LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/

Issued at 349 AM MDT Tue Oct 13 2026

Primary forecast concern will be the Pacific storm system expected to move across the region midweek, bringing widespread rainfall, mountain snow (down to elevations of 7500 feet, possibly lower but limited confidence), windy conditions, and much cooler temperatures.

All models show the potent mid to upper level low lifting northeast across Colorado Wednesday night, and gradually into southern Nebraska by Thursday. Both the ECMWF and GFS deterministic show this general trend, with the 500mb low tracking across northeast Colorado. The surface low is quite a bit south, so not expecting (so far) a "slow" stacked storm system at this time with the surface low developing across eastern Colorado and tracking east-northeast into eastern Nebraska by early Thursday morning. However, the NAM and Canadian are further north with the storm system, showing it hugging the CO/WY border with a pronounced dry slot moving into the eastern plains Wednesday night. Due to these remaining uncertainties, did not increase QPF too much Wednesday night through Thursday, but expect a decent rainfall for most of the eastern plains given good upslope flow, persistent isentropic lift, and some jet dynamics due to an exiting 110 knot jet max. Precipitation and precipitation type is a little less clear further west, mainly along and west of the I-25 corridor. Models have trended a bit colder, likely due to some dynamic cooling with this storm system. 700mb temperatures are now between -2c to -5c across the area. With an isothermal layer noted between 1500 ft to 5000 ft on area soundings, this is cold enough to support snow, at least, down to 7000 feet...including the Laramie valley and the high valleys across Carbon County. Further east, it is very close for elevations down to 6000 feet, including Cheyenne, where a mix rain/snow is certainly possible Wednesday night into Thursday morning. Based on current model and ensemble data, intermittent change over(s) to snow and rain/snow mix are expected between 6500 to 7500 feet where some light accumulation possible on grassy and elevated surfaces. However, most of these valleys (west of the Laramie Range) will struggle with some easterly downslope flow off the Laramie Range as winds start to increase and shift east and southeast. This is why POP is a bit lower for Laramie, Saratoga, and Rawlins. High confidence that the mountains will receive accumulating snowfall with Winter Weather Advisory conditions expected Wednesday through Thursday. May need to issue these shortly, but we have additional time to fine tune the accumulation details. The bigger question is the Arlington/Elk Mountain are and the I-80 Summit between Laramie and Cheyenne. Currently, snowlevels are low enough to warrant Winter Weather Advisory amounts. However, not very confident on QPF amounts in this area and if any snow will stick to the roadways. Will continue to monitor this potential with future updates.

Otherwise, models have trended a bit stronger on winds late Wednesday night and Thursday with a stronger pressure gradient behind the surface low and 700mb winds increasing out of the north between 40 to 50 knots. North winds gusting up to 45 MPH possible through Thursday afternoon across the eastern plains.

Precipitation will diminish from west to east Thursday into early Friday morning with clearing skies. This is our most favorable period to see frost and a hard freeze. Currently, forecast low temperatures are in the 20s to near the upper teens across south central Wyoming, including the Laramie Valley. Mid 20s to low 30s forecast for the eastern plains. This is generally around the 25th to 50th percentile of the NBM and the 12z Grand Ensemble which seems to fit this general pattern as some colder air sneaks around the backside of the storm system Thursday night. Would like to note that the new 00z Grand is even colder with 25th percentile lows around the mid teens to low 20s. Freeze and/or Frost headlines expected, but will wait until this storm is through the area first. Friday will be seasonably cool under northwest flow aloft with highs in the 50s to low 60s.

Medium to Long Range models appear to be in reasonable agreement for next weekend, showing a broad ridge axis translating eastward into the Front Range from the eastern Pacific. Expect drier weather with pleasant daytime temperatures for mid October with highs in the 60s to low 70s...and some mid 70s for western Nebraska. Low temperatures will be seasonable and generally in the 30s to low 40s into next Monday morning.

AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/

Issued at 545 AM MDT Tue Oct 13 2026

Strong Pacific storm system beings to track east towards the area today as a stationary front lingers across the mountains of southeast Wyoming. Rain showers and areas of fog continue this morning with a brief break this afternoon and into early this evening as the stationary cold front temporarily lifts northeast as a warm front. Another round of showers and possible thunderstorms this evening through tonight.

HAZARDS/WEATHER TRENDS: Widespread (L)IFR and patchy fog will continue for all western Nebraska terminals and KCYS until 16z to 19z with gradual clearing through the afternoon. A brief break in the shower activity until this evening. Confident enough to add TS to a PROB30 group for KLAR and KCYS. Otherwise, shower activity and MVFR VIS and CIGS will redevelop from west to east after 04z Wednesday with IFR conditions possible after 06z across the southeast Wyoming terminals in periods of rain showers.

CYS WATCHES/WARNINGS/ADVISORIES

WY...Dense Fog Advisory until 7 AM MDT this morning for WYZ116-117. NE...None.