textproduct: Cheyenne

KEY MESSAGES

- Cooler temperatures will prevail for the rest of the week with widespread showers this evening through Thursday morning.

- Accumulating snow will develop in the higher peaks tonight, and then spread to areas above about 7000 ft in elevation Wednesday evening into Thursday morning.

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

SHORT TERM /THROUGH THURSDAY/

Issued at 300 PM MDT Tue Oct 13 2026

Our area is in the midst of a lull in precipitation chances as a region of dry air moves overhead. While clouds are hanging on in parts of the Nebraska panhandle and into Converse and Niobrara counties, sunshine is breaking through elsewhere, allowing for a pleasant day with fall-like temperatures. However, the sprawling upper level low currently over the Las Vegas area will continue to meander closer to the area, bringing another round of moisture and lift into the area later this afternoon. Isentropic lift kicks up aggressively by late afternoon in Carbon and Albany counties, spread into the I-25 corridor and points east this evening, and finally the Nebraska panhandle after midnight. As the strong forcing expands, shower activity will spread with it. Look for numerous to widespread showers developing in the west and spreading east, with some isolated embedded thunderstorms expected as well. With abundant moisture in the atmosphere, rainfall should be fairly efficient. Most rainfall will be light, but expect periods of moderate to heavy rainfall to occur intermittently through the night. Snow levels overnight tonight will be fairly high, around 10 kft to start, and dropping to around 9 kft by morning.

Easterly upslope flow will become more organized overnight. With a decent reverse gradient developing, expect to see a wind gusts in the 25 to 35 mph range in Carbon and Albany counties. Winds will be weaker to the east, but steady. Excellent moisture advection will bring in plentiful low cloud cover and upslope fog across the area for Wednesday morning. High resolution models are in good agreement showing the area remaining largely socked in for most of the day Wednesday, at least along and east of the Laramie Range. More breaks in the cloud cover can be expected in Carbon and Albany counties where easterly flow is locally downslope. Thick cloud cover will keep temperatures cool. The NBM seems unrealistically warm, so maximum temperatures were blended to the NBM 10th percentile and the HRRR, resulting in highs generally in the 40s for the entire area. The storm system will begin a transition phase beginning around the late morning hours tomorrow, but there is some timing uncertainties. As the axis of the upper level low gets closer to the area, isentropic lift on the leading edge of the system will weaken slightly. In addition, an area of drier air above 500-mb will move over the area. Expect precipitation rates to decrease considerably as this occurs, which will be roughly mid morning Wednesday to the early evening.

Once the axis passes our area, which looks to occur sometime between sunset and midnight Wednesday evening, the storm system will develop a more pronounced TROWAL, wrapping moisture back into the area with strong isentropic lift. Once this occurs, expect precipitation coverage and rates to increase again, filling in over much of the area. While the Nebraska panhandle will probably struggle with precipitation amounts during the first phase of the event, the area should do better in this phase, though there is some uncertainty in the exact location and spatial extent of the TROWAL and associated forcing. Colder air will also move into the area behind the trough axis, leading to crashing snow levels through the night and into Thursday morning. Confidence is now high in accumulating snow above 8000 ft, and the probability for accumulating snow is increasing as low as 6000 ft in elevation. Thus, the primary uncertainty elevation band includes both Laramie and Cheyenne. Precipitation will end Thursday morning or early afternoon as dry air moves into the area behind the storm system. With clearing skies, winds becoming light, and a cool airmass in place, expect a widespread freeze Thursday night into Friday morning.

MOUNTAINS: With accumulating snow likely to begin tonight in the Snowy Range, confidence was high enough to issue a Winter Weather Advisory beginning and midnight and continuing through Thursday midday. The first phase of the event will be more showery and intermittent through Wednesday early evening, with more consistent snowfall expected overnight and into Thursday morning. That being said, high end probabilities are also increasing, such that there is about a 40% chance to exceed 12" in the higher peaks of the Snowy Range. This will need to be monitored going forward. Due to a less favorable upslope wind direction, the Sierra Madre range was not included, but probabilities for 6" or more (spread over a 36 hour period) are around 50% at this time.

I-80 CORRIDOR: The next highest confidence in snow impacts is along the higher elevations of the I-80 corridor, including the summit between Laramie and Cheyenne, and the Arlington/Elk Mountain area. However, snow levels will only drop to these elevations tomorrow afternoon or so, so we have time to wait and evaluate trends for another model cycle. Probabilities for advisory criteria snowfall are around 70% for both zones, and there is a 30% chance to reach warning criteria amounts. Arlington and Elk Mountain often over-perform during northeasterly upslope flow events, so headlines may be needed with later forecast updates.

LARAMIE & CHEYENNE: Once the trough axis passes, winds will turn from northeast to north or northwest. Models are in good agreement showing NNW winds in the Laramie Valley as colder air is pulled into the system. LREF median 700-mb temperatures are around -3 to -5C between Laramie and Cheyenne. At this time, Laramie is likely to flip over to snow and see accumulation Wednesday night into Thursday morning, and Cheyenne is right on the edge due to the extremely marginal temperatures. Laramie has a 80% chance for an inch of snow, and approximately a 10% chance to exceed 4" per the latest NBM probabilities. However, the timing of the event (early morning), combined with a very favorable surface wind direction suggests potential for a boom scenario in and around Laramie. The HRRR shows an excellent example of this boom scenario which is also around the 75th percentile of the ECMWF ensemble. For now, the official forecast is fairly conservative, but this scenario is probable enough to discuss and watch closely over the next 24 to 36 hours.

ELSEWHERE: Accumulating snow is unlikely below about 5000 ft in elevation, with precipitation expected to remain all rain. This storm should bring widespread wetting rainfall to the entire area. Most likely QPF amounts remain generally between 0.5" and 1.0" for the majority of the forecast area. Confidence in reaching 0.5" is lowest north of a Douglas to Chadron line, and in western Carbon county outside of the mountains. Expect to see snow mixing in other areas of Carbon and Albany counties, but the probabilities for impacts are fairly low.

LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/

Issued at 300 PM MDT Tue Oct 13 2026

After a potent, multi-day storm event, the end of the week and into the start of next week, will be quiet with a return to warmer and drier weather. Once the low pressure system responsible for the ample mid-week moisture moves east out of the area, upper-level ridging will take its place. The ridge will usher in warmer air aloft, allowing surface temperatures to rise. Subsidence under the ridge will keep cloud cover away, helping to amplify high temperatures during the day. On Friday, temperatures will rebound back to seasonable, with highs reaching the 50s and 60s. By Saturday, temperatures will be back above average as 700 mb temperatures reach the 90th percentile of NAEFS climatology. Highs east of the Laramie Range will reach the 70s, leading to a warm fall day.

The ridge will flatten out briefly on Sunday as a shortwave passes south through the Four Corners region. Impacts from this shortwave will be minimal, with high temperatures only falling a few degrees compared to Saturday. Expect a breezier day on Sunday as well with strong west winds in the typical southeast Wyoming wind prones. Warm and dry conditions continue once again into the start of the work week. Temperatures will remain above average for Monday and Tuesday with dry conditions expected both days. Precipitation chances begin to increase Tuesday night as a deep trough pushes into western CONUS.

AVIATION /06Z TAFS THROUGH 06Z THURSDAY/

Issued at 1130 PM MDT Tue Oct 13 2026

Primarily MVFR and IFR will prevail through the TAF period as numerous showers and perhaps a few thunderstorms are expected to occur overnight into tomorrow. Expect MVFR CIGs overnight for most terminals based on latest METARs under the ENE upslope flow. Not expecting much in the way of any VIS reductions aside from underneath any of the heavier showers. High-resolution ensemble guidance continues to show IFR CIGs for KCYS after 09Z under a cold air damming regime banked up against the Laramie Range. KLAR and KSNY may see some of these IFR CIGS as well based on current high res data. Can expect brief periods of IFR tomorrow evening after 00Z as another round of showers is expected to impact SE Wyoming and the Nebraska Panhandle.

CYS WATCHES/WARNINGS/ADVISORIES

WY...Winter Weather Advisory from midnight tonight to noon MDT Thursday for WYZ114. NE...None.