textproduct: Cheyenne

KEY MESSAGES

- Chances for scattered rain and snow will continue through Thursday night.

- Warmer and drier conditions are expected to return for Friday into the weekend.

SHORT TERM /THROUGH THURSDAY NIGHT/

Issued at 245 AM MDT Wed Apr 29 2026

Our area is in between upper level shortwave troughs this morning, leaving fairly tranquil conditions. A weak surface high over the central Plains is producing light southerly winds over most of our High Plains zones, which is keeping dewpoints elevated this morning. With mainly clear skies and light winds, we are seeing some patchy fog and low clouds developing. The main area of this is apparent on GOES satellite imagery, just on the cusp of Sidney and Alliance, and expanding westward up the North Platte River Valley. Observations also indicate some very patchy radiation fog developing elsewhere over the area, but those locations are not large enough to present on satellite imagery. As the surface high retreats further east, the westerly component of the surface wind will increase slightly, but this should be enough to hold the fog from expanding much further to the west (except in the river valley). Any remaining fog should burn off fairly quickly after sunrise today as northwest winds overspread the area.

The next subtle shortwave currently visible on satellite imagery over central Utah will approach the area this afternoon. This feature will help kick off another round of scattered rain and snow showers late this morning or early in the afternoon in the place of modest convective instability expected to develop. Forecast soundings show a fairly pronounced stable later right around 500-mb this afternoon, which will put a fairly low height limit on developing convection. This will in turn limit the potential for rainfall today. The highest chance for seeing more than a few sprinkles is along our eastern row of counties from Chadron south towards Sidney. We will also need to watch the vicinity of the Laramie range and the higher mountains of southeast Wyoming where the boost from orographic lift and some low-level convergence may help anchor some shower activity. In these areas, precipitation type will probably be snow.

Meanwhile, another upper level shortwave will dive down from the north tonight. This will be accompanied by a diffuse surface cold front supporting cold air advection beginning this afternoon and surface pressure rises from north to south. Overnight into Thursday morning, this surface high will push up against the higher terrain of southern Wyoming and stall as the messy shortwave trough inches southward. Models show some modest frontogenesis and overrunning developing along the WY/CO border during this period. A few models also show some similar forcing developing in northern Carbon and Albany counties along the more subtle terrain barrier in that area. This should support another round of developing shower activity. Overall, this system is now expected to take a track that is unfavorable for widespread precipitation for our area. Most of the area will unfortunately see little to no beneficial moisture, but there is still a sliver of hope for the Cheyenne to Elk Mountain corridor. Current probabilities for 0.10" or more of liquid precipitation are around 30 to 50% in Cheyenne, Laramie, and Elk Mountain. This increases to 50 to 70% increasing in elevation around the Snowy Range (especially the east side) and the southern Laramie Range / I-80 summit. Further north, probabilities fall to 10 to 30% in Rawlins, Wheatland, Kimball, and Sidney, and then drop to near zero along and north of the North Platte River Valley. Snow will be the dominant precipitation type, but expect to see a rain/snow mix below about 7000 ft in elevation. We currently have approximately a 20 to 30% chance for reaching Advisory criteria snowfall in the Snowy Range and I-80 summit areas. The timing is a little tricky, but expect this to pick up late tonight or early Thursday morning, and continue through the afternoon before tapering off Thursday evening. Some isolated thunder is also likely with this activity.

LONG TERM /FRIDAY THROUGH TUESDAY/

Issued at 245 AM MDT Wed Apr 29 2026

The unsettled weather pattern will pause Friday morning as the messy shortwaves / upper level low gets pushed south into New Mexico. A disorganized ridge will try to expand into the northern Rockies over the top of this system. While the pattern will remain messy, models are in fairly good agreement that we will see warmer and drier weather return to the area to begin the month of May. 700-mb temperatures will climb to around -2 to 0C on Friday, then +2 to +4C for Saturday, and Sunday. Expect high temperatures near average on Friday, then climbing above average for Saturday and Sunday, by about 10F. Drier air will also work back into the area with precipitable water values approaching the climatological 10th percentile. This will push humidity back down to near or below critical thresholds and increase fire weather concerns. However, the bright side is that the highly disorganized upper level wind field should keep winds fairly light across the area, keeping Red Flag concerns at bay at least for Friday and Saturday. Winds are expected to tick upwards Sunday, but mid to upper level moisture will begin to recover as well. Expect a few high-based PM showers to return to the forecast Sunday.

Looking ahead into the early part of next week, we should start to east back into a more unsettled weather pattern. The primary player on the synoptic scale will be a large, sprawling upper level closed low slowly meandering inland from the West Coast. Meanwhile, the persistent upper level low over the Hudson Bay will continue to spin over the area, sending occasional weak shortwave troughs dropping down from the north. The current most likely outcome is for continued mild temperatures on Monday and Tuesday with daily chances for PM showers and thunderstorms. By the very end of the forecast period towards next Wednesday, the primary closed low may be arriving near our area, which will increase the chances for a cool down and widespread stratiform precipitation. Confidence remains very low in any details concerning precipitation amounts or timing.

AVIATION /06Z TAFS THROUGH 06Z THURSDAY/

Issued at 1145 PM MDT Tue Apr 28 2026

The main concern tonight will be fog at KSNY and KAIA which can be seen on GOES nighttime microphysics imagery as clear skies combined with weak upslope flow is in place. Ogallala is currently reporting fog as well, so decided to add these into the TAFs until 12Z before the low-level moisture begins to mix out and winds turn more westerly. Can expect LIFR conditions in these conditions, although confidence regarding exact timing and longevity is moderate (40-50% chance).

For the remaining terminals, a combination of VFR and MVFR conditions will prevail as CIGS lower below 3 kft in the vicinity of any showers tomorrow afternoon. Shower coverage is expected to increase after 18Z before winding down shortly after sunset. Expect 5-10 knot SW flow to veer to more westerly during the day, before turning to northerly through the remainder of the TAF period.

CYS WATCHES/WARNINGS/ADVISORIES

WY...None. NE...None.