textproduct: Cheyenne

KEY MESSAGES

- An powerful cold front arriving Monday will bring a chance for showers and thunderstorms, changing over to snow Monday night and continuing into Wednesday morning.

- Accumulating snowfall is expected over 5500 feet in elevation, with significant snowfall likely (70% chance) in the Snowy Range, southern Laramie Range, and their adjacent foothills.

- Travel impacts due to snowfall are expected along Interstate 80 between Rawlins and Cheyenne, and Interstate 25 between Wheatland and the Colorado state line.

- Impacts may extend eastward on Interstate 80 towards Kimball, but confidence is lower for areas below 5500 feet in elevation. - Snowfall is expected to be heavy and wet, which could damage tree limbs and produce power outages.

- Drier, warmer, and windier weather returns to the area for the second half of the work week.

SHORT TERM /THROUGH WEDNESDAY/

Issued at 402 PM MDT Mon May 4 2026

Tonight through Wednesday (The system): The RRFS has the front moving through this evening around 6pm. This front will be the start of the system as the moisture begins to lift and showers begin to develop. The 12z Hi-Res models have a band of Frontogenesis (FGEN) or enhanced precipitation right along the Colorado border and sort of fill in amongst the mountain ranges. The snow levels will drop quickly overnight going from about 9,000ft to 7-6,000ft by midnight and then finally dropping below topography (4-5,000ft) by Tuesday morning. This should quickly transition from rain to snow but in the mountains and mountain adjacent areas. The band of enhanced snowfall (FGEN) should temporary stall along the Colorado border increasing snow rates and cooling down the ground to allow for measurable accumulation instead of melting. Tuesday, a reinforcing upper level shortwave will push through the Intermountain West. This wave will push another stream of vorticity to help aid in the overall lift in the northern half of our forecast area well as strengthen the isentropic lift over the southern half and mountains. The Hi-res models do develop another band of FGEN with this secondary trough. This will essentially continue the snow showers in the mountains with a rain/snow mix along and east of the I-25 corridor to the Nebraska Border. The rain/snow mix may extend into Kimball,NE as the heavier rates should keep it as such. But for most of the Nebraska Panhandle, the precipitation will likely stay as rain from Tuesday morning through the evening. Tuesday night into Wednesday morning, A reinforcing shot of cold air overnight will transition the rain showers into light snow. The snow showers are expected to start tapering off through the afternoon. By Wednesday evening the showers should have either dissipated or continued to follow the trough moving southeast to not be our problem anymore.

SNOW ACCUMULATIONS: The Hi-res models have really ramped up snow accumulations due to their placement of the band of FGEN. The 12z model of the HRRR had snow accumulations between 14 to 18 inches of snow for the CHeyenne area while the RRFS 12z run had between 8 to 10 inches. The ensemble means were used for the total snow accumulations between the Euro/GFS/and Canadian Ensembles. The euro ensemble mean was more heavily weighted as it seemed to do a better job of the Snow shadowing that occurs over Laramie in easterly flow due to the previous down sloping environment mentioned. So the snow totals were updated to between 8-12 inches for Cheyenne, 4-6 inches for Laramie and 2-4 inches for Rawlins. Do to the progged placement of the strong FGEN the models converged on the Summit and Foothills area and along I-80 between elk mountain and Cheyenne to receive about 12-18 inches of snow. So that range has been roughly consistent so totals were kind of left alone. The ensembles had about 18-21 inches for the Snowy range and the Sierra Madre range 10- 13 inches. A Winter Weather Advisory was put out for the Sierra Madre mountain range and the Winter Weather Watch was upgraded to a Winter Storm Warning for the Central Laramie County area based upon the new snow accumulations.

IMPACTS: Another challenge with this system is the degree of impact. On one hand, the time of year and warm ground temperatures suggest lesser accumulation on roadways. However, that doesn't mean zero, especially for any snow that falls at night. Roadways will probably be slushy and slick late tonight through Tuesday, but then there could be some re-freezing and icing concerns Tuesday night into Wednesday morning as colder air moves into the area. In addition, the snow is expected to be very heavy and wet. Thanks to the exceptionally warm spring weather so far, deciduous trees are leaving out across the area. Therefore, the snow weight is expected to strain or break tree limbs, which could lead to some downed powerlines and power outages across the area. These concerns will need to be closely watched over the next 24 hours as the storm system gets going.

LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/

Issued at 445 AM MDT Mon May 4 2026

The axis of the strong upper level shortwave trough is expected to pass over the area Wednesday morning, which should abruptly conclude the widespread lift, and also begin to advect in drier air aloft. While some snow shower activity may linger into Wednesday afternoon, we should be mostly done with the system by midday. The strong sun will help to melt snow and improve travel conditions quickly, especially as clouds clear in the afternoon hours. Wednesday will still be quite chilly across the area, with highs expected in the upper 40s to low 40s in areas receiving accumulating snow from this system, and upper 40s to mid 50s elsewhere. Ridging will try to build in across the western US by Thursday. Our area will remain on the periphery of the ridge. Initially, expect a period of increased winds as warm air advection takes over. Probabilities for high winds remain around 20 to 40% in the wind prone areas on Thursday. Still, a windy day can be expected for much of the area as temperatures recover to near or slightly above seasonal averages.

The area is expected to remain under a fairly unsettled northwest flow pattern through the end of the operational forecast period. While temperatures will most likely recover to near normal, global model guidance keeps a parade of upper level shortwaves moving through the area every day or two. There are significant disparities in timing and strength of each shortwave, which makes it difficult to get into the details. The make take away is that the unsettled weather pattern will keep chances for showers in the forecast for much of the long term period. There is potential for another system to tap into some cold air by the upcoming weekend, but only a handful of ensemble members are cold enough for snow levels to drop to the level of our populated areas.

AVIATION /18Z TAFS THROUGH 18Z TUESDAY/

Issued at 1122 AM MDT Mon May 4 2026

A rather strong cold front for early May will sweep southward across the terminals this afternoon and evening, ushering in a colder airmass with widespread rain and snow south of a Rawlins to Scottsbluff line, and less areal coverage further north.

Wyoming TAFS...High confidence in ceilings lowering from 8000 to 12000 feet, to 5000 feet this evening, then further lowering to MVFR late this evening, then to IFR late tonight and Tuesday morning. Low confidence in isolated thunderstorms this afternoon producing wind gusts to 30 knots and visibilities from 4 to 6 miles. High confidence in widespread rain and snow showers developing this evening, changing to all snow late tonight, with widespread IFR due to visibility and clouds. After cold frontal passage, winds gusting to 30 knots most of the period at Rawlins, and into early evening at Laramie and Cheyenne due to thickness packing behind the cold front.

Nebraska TAFS...High confidence in ceilings gradually lowering this evening to low VFR, and remaining VFR at Chadron and Alliance through the period, while Scottsbluff and Sidney have ceilings and visibilities lowering to MVFR after 06Z in rain and snow showers, then IFR at Sidney late tonight and Tuesday morning. After cold frontal passage, surface pressure packing and cold air advection will help produce wind gusts to 35 knots for 3 to 6 hours after the cold frontal passage.

CYS WATCHES/WARNINGS/ADVISORIES

WY...Winter Weather Advisory from 9 PM this evening to 9 AM MDT Wednesday for WYZ103. Winter Weather Advisory from midnight tonight to 9 AM MDT Wednesday for WYZ105-106-115. Winter Storm Warning from 9 PM this evening to noon MDT Wednesday for WYZ110-114-116-117. Winter Weather Advisory from 6 AM Tuesday to 6 AM MDT Wednesday for WYZ112. Winter Storm Warning from midnight tonight to 9 AM MDT Wednesday for WYZ118. NE...None.