textproduct: Cheyenne

KEY MESSAGES

- A messy pattern is anticipated today through much of the upcoming week, allowing for ongoing precipitation chances across the entire CWA. The best chance for precipitation will be Sunday, with widespread showers and thunder.

- A Winter Weather Advisory has been issued for the Sierra Madre and Snowy Ranges from 6PM Saturday through 6AM Monday.

SHORT TERM /THROUGH MONDAY/

Issued at 310 AM MDT Sun Apr 26 2026

Dense fog is being observed along the I-80 Laramie Foothills to Cheyenne, visibilities are down to a quarter mile. Another area of patchy fog is being observed along I-20 near Sidney. This advection fog is likely to persist into the morning hours per the latest HRRR guidance and using observation persistence from the last two days. Radar is picking up scattered rain and snow showers along the Rawlins, Pine Ridge, and Chadron corridor. Temperatures will top out today in the 50s for most places, the interior mountains and north of the North Platte River Valley will be in the 40s. Instability is lacking to form thunderstorms this morning, however as the upper level disturbance passes over this afternoon, the chances for storms increases. Hi-res models are highlighting an area of 400-700 J/kg of SBCAPE for portions of the intermountain ranges. Lightning density products from these models are low which makes sense given the thermodynamics. Also, given the low freezing levels paired with 40 kts of storm effective wind shear, it is not out of the question that small hail occurs in the most vigorous updrafts. Outside the storm potential we also have a winter weather advisory out for the Sierra Madre and Snowy Ranges through sunrise Monday. This is primarily for the peaks, but our outlook is for 6-12 inches of snowfall. This will most likely be spread out over two burst in snowfall, one through today and again overnight Monday. Although shower and storm activity is expected to be scattered in nature, most locations will likely receive some form of precipitation. QPF ranges between 0.15" to 0.5" over much of the area. As the initial shortwave departs the precipitation chances fall, but with near or below freezing temperatures, shower activity may convert to snow or mix by daybreak. Outside the mountains most areas may only receive a trace to a few hundredths of an inch. Some parts of northern Converse County may see an inch to two inches of snow. Winds shift to out of the northwest and increase Monday morning as a surface low develops and moves east of our location.

LONG TERM /MONDAY NIGHT THROUGH SATURDAY/

Issued at 310 AM MDT Sun Apr 26 2026

The upper-level trough will slowly deepen and continue its slow eastward progression throughout the day Monday. A subtle positive tilt to the approaching trough will develop Monday evening, though upper-level flow remains largely weak. A weak 500mb ridge will undercut the upper-level trough, continuing the messy pattern that has been in place over the past several days. 500mb vorticity advection will push into the region behind the weak shortwave ridge and just ahead of the incoming upper-level trough. This cyclonic vorticity advection (CVA) will help the trough move eastward a touch quickly, while also providing synoptic ascent across the region. The messy 700mb flow will continue Monday with a brief ridging developing before advecting off to the east and being absorbed into the lower-level flow by Monday night. Warm air advection (WAA) is expected to be fairly strong across the County Warning Area (CWA) in the afternoon, further supporting synoptic ascent across the region. Looking at the surface, northerly flow behind a cold front on Sunday will keep the region cooler, in the 40s and 50s everywhere, with increasing clouds throughout the day. By Monday afternoon, another surface high is progged to develop off the Black Hills of South Dakota, leading to surface flowing turning from the north to a more easterly to southeasterly direction. Precipitable Water values (PWs) will be average for this time of year per the NAEFS mean and climatological percentile, so significant precipitation is not anticipated. However, the moist, easterly upslope flow will enable continued shower development across the region east of the Laramie Range. As a result, another cloudy, cool, and wet day is in store for Monday. Temperatures are expected to remain warm enough to primarily get rain east of the Laramie Range, but a transition to snow is possible into the overnight hours after the sun sets.

On Tuesday, the upper-level trough that has been parked across the Intermountain West will start to lift northeastward into eastern Canada, with largely zonal flow developing in its wake. A strong, subtropical upper-leve jet will push northward and remain just south of the CWA, leading to largely benign weather for Tuesday. Broad, northwesterly flow is anticipated at 700mb, with weak WAA expected throughout the morning and afternoon hours. With added ascent to the region from 700mb WAA, the sky will remain mostly cloudy, prohibiting surface temperatures from increasing too much during the day. Largely northwesterly flow is expected at the surface, with isolated to scattered showers east of the Laramie Range and isolated to scattered snow showers west. Temperatures will rise into the 50s and 60s everywhere. Accumulation is not anticipated to be significant, but another day of rain/snow will be appreciated across the region.

Wednesday through the end of the long term period will be largely dominated by a develop upper-level trough that will be slow to initiate and become messy fairly quickly. An upper-level ridge just off the western coast of the CONUS will slowly move on shore and amplify Wednesday and Thursday, but poor 500mb vorticity advection will cause this ridge to essentially collapse and lead to a cut off low developing by Friday morning before being absorbed into a larger scale trough by Friday afternoon. By Saturday afternoon, this low will have been absorbed into the flow as weaker ridge develops over the Intermountain West. 700mb flow remains weak with limited feature of note through the weekend. With the messy upper-level patter with minimal support for synoptic ascent, conditions are anticipated to start drying out Wednesday through the end of the week with fire weather concerns starting to sneak back into the region by the weekend. After a cool day on Thursday as the cutoff low turning into an upper-level shortwave impacts the region and decreases temperatures, a strong warming trend will return with highs back into the 60s and 70s for the weekend.

AVIATION /12Z TAFS THROUGH 12Z MONDAY/

Issued at 518 AM MDT Sun Apr 26 2026

A challenging forecast this morning across much of the region. Cloud decks have dropped well below LIFR and into the VLIFR conditions at KCYS, KLAR, and KSNY. Fog has been rolling across many terminals, oscillating the visibility from around 1/2 mile to 3 miles across many terminals. This oscillation will continue through the morning hours, with brief periods of improved visibility, but very low ceilings will remain. Ceilings will start to lift in the afternoon hours before isolated to scattered showers and storms develop from southwest to northeast. Any shower or storm that develops will be capable of producing gusty and erratic winds. Best chance of storms will be at the KCYS, KLAR, and KSNY where PROB30 groups have been added to the TAFs. Ceilings begin to drop once more this evening into the overnight hours with visibilities following soon after.

CYS WATCHES/WARNINGS/ADVISORIES

WY...Winter Weather Advisory until noon MDT today for WYZ112-114. Dense Fog Advisory until noon MDT today for WYZ116-117. NE...None.