textproduct: Cheyenne

KEY MESSAGES

- Elevated to critical fire weather conditions continue today. A Red Flag Warning has been issued for Laramie County.

- Widely scattered showers and isolated thunderstorms are expected this afternoon and evening, and may produce gusty and erratic winds.

- 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 likely (70% chance) over 6000 feet in elevation, with significant snowfall possible in the Snowy Range, southern Laramie Range, and their adjacent foothills.

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

SHORT TERM /THROUGH TUESDAY NIGHT/

Issued at 410 AM MDT Sun May 3 2026

SUNDAY OVERVIEW: The strong ridge aloft is beginning to weaken this morning as it is compressed from both the north and the west by troughs. A shortwave aloft dropping down from the north today is contributing to increased mid to high level cloud cover across the area. A weak surface high is following this system, and is analyzed over the western Dakotas this morning. Higher surface pressure pushing up against the Laramie Range has led to slightly improved humidity, but the I-80 corridor remains quite dry. Mid to upper level moisture is recovering nicely today, but this is overtop a very dry boundary layer in some areas. After sunrise today, a surface trough is expected to develop along the I-25 corridor and nudge the better moisture slightly off to the east today. It should stall around the North Platte River. To the south and east, expect near critical fire weather conditions to return with RH between 12 and 20% and northwest winds gusting 20 to 30 mph. Confidence in critical conditions was high enough to issue a Red Flag Warning for the Laramie County, but we will need to watch areas of Converse, Platte, and Goshen counties for a possible expansion later. Today's highs are generally expected to be near or slightly cooler than yesterday with the increased cloud cover, but still about 10F above seasonal averages.

SUNDAY STORMS: North and east of the moisture boundary, we should have enough surface moisture to develop modest instability. RAP soundings indicate about 300 to 700 J/kg of SBCAPE along the US-20 corridor. The approaching upper level shortwave will kick off weak overrunning lift this afternoon which should help kick off widely scattered showers and isolated thunderstorms that will be able to tap into this instability. Elevated winds aloft particularly closer to South Dakota will produce some deep layer shear, but currently the instability looks weak enough to keep storms sub-severe. However, a rogue stronger storm cannot be ruled out around Niobrara, Sioux, and Dawes counties. For the most part, this activity will just produce gusty and erratic winds.

MONDAY OVERVIEW: Monday will be a transition day across the area as a powerful cold front approaches from the north. A very complex synoptic weather pattern up will be developing Monday, setting the stage for a few days of much colder weather and precipitation potential. Two major players will be on the board this week. First, an expansive but not particularly deep upper level closed low currently off of the California coast will meander inland by Monday. Second, an unseasonably strong upper level low locked in over the Hudson Bay will retrograde westward and send a series of strong vort-maxes down from the north. In isolation, neither of these features would be favored to provide much precipitation potential, but the interaction between the two (i.e. forcing for lift associated with the northern branch systems in place of plentiful Pacific moisture contributed by the closed low) makes this a more interesting forecast. Monday will start off mild, but the surface cold front is expected to pass through during the day. This may reach Douglas to Chadron by 7AM or so, stunting high temperatures there for the day. The front should reach the I-80 corridor by midday. As a result, expect most areas to see a morning or early afternoon high temperature, with gradual cooling through the afternoon hours. After sunset, temperatures will begin to rapidly cool. The surface front will slow down as it pushes up against the higher terrain of southern Wyoming and northern Colorado, leading to frontogenesis. Forecast soundings along the I- 80 corridor Monday afternoon look nearly saturated with fairly steep lapse rates in place. SBCAPE could locally exceed 1000 J/kg. Strong forcing provided by the frontogenesis and moderate overrunning flow should kick off numerous showers and scattered thunderstorms around midday Monday, mostly along the I-80 corridor. A few stronger storms capable of producing hail and gusty winds cannot be ruled out.

MONDAY NIGHT THROUGH TUESDAY NIGHT OVERVIEW: After sundown Monday, precipitation will begin to transition from a showery convective type towards more stratiform precipitation as the instability dissipated and forcing continues to strengthen. Very potent cold air advection will be present through this transition, sending snow levels tumbling Monday night into Tuesday morning. The higher elevations of I-80 should switch to snow Monday evening, and the populated areas above 6000 ft including Laramie and Cheyenne should be seeing all snow by daybreak Monday. For lower elevations, the precipitation type will probably be dependent on precipitation rate. During periods of heavier precipitation rates, expect to see snow, whereas lighter periods may switch back to rain. Therefore, the official forecast includes a rain/snow mix for most of these areas during the day Tuesday. Most model guidance shows the strong frontogenesis slipping south into Colorado during the day Tuesday, but weak isentropic lift / positive theta-e advection should maintain light to moderate precipitation along the I-80 corridor. Another, stronger vort- max will dive down from the north Tuesday PM, reinforcing the cool air and perhaps providing another slight boost to forcing via enhanced frontogenesis. The axis of this trough will pass through the area by Wednesday morning, bringing much drier air in aloft and abruptly shutting off precipitation.

PRECIPITATION PROBABILITIES: While we have a pretty solid idea of the overall evolution of this system at this time, there are still plenty of details to sort out, mainly concerning QPF, how much of that QPF falls as snow, and how much of that snow manages to stick. Ensembles remain in good agreement on the overall QPF picture with only minor changes over the last 24 hours. Beneficial precipitation remains most likely south of the North Platte River, whereas areas to the north will see weaker forcing and thus much lower precipitation totals. The latest NBM probabilities for 1" or more of QPF are around 50% in Cheyenne, 40% in Laramie & Sidney, 20% in Wheatland & Scottsbluff, and 10% or less further north. For 0.5" or more, this increases to 90% in Cheyenne, 75% in Laramie & Sidney, 50% in Wheatland & Scottsbluff, and 30% or less further north. Ensembles are nearly unanimous in showing beneficial precipitation in the I-80 corridor between Elk Mountain and Sidney, with even the NBM 10th percentile exceeding 0.25". That low end scenario could still play out though. The primary failure mode appears to be the case in which the frontogenesis breezes through quickly and sets up to our south, leaving light precipitation Tuesday and Tuesday night. Currently there is about a 20% chance of this failure mode, which would lead to little to no precipitation north of the North Platte River, and 0.1 to 0.4" further south.

SNOWFALL PROBABILITIES: This system will be quite cold for this time of year. 700-mb temperatures drop to below the climatological 10th percentile, bottoming out around -6 to -10C early Wednesday morning. Confidence is increasing in accumulating snow falling above about 6000 ft in elevation, and significant snow above about 7500 ft (mainly east and northeast facing slopes). The most favored area is currently the southern Laramie Range where frontogenesis and favorable easterly upslope flow should deliver a prolonged period of snow. The eastern and northern sides of the Snowy range will have similar dynamics. Confidence was high enough in these areas to issue a Winter Storm Watch as the probability for 6+" of snow has increased over 50%. We will need to watch adjacent zones too, as even Laramie and Cheyenne have a 30-40% chance for exceeding 6". These areas have the extra variable of whether snow will stick or not, making confidence too low to include in the watch at this time. The current most likely scenario for those areas is a solid Advisory level event in the 3 to 6" range. Accumulations will also depend on the timing, as snow falling during the day will be much less likely to stick and accumulating thanks to the very strong early May sun. We will therefore wait a little longer for confidence to improve before including lower elevation zones in any winter weather headlines.

LONG TERM /WEDNESDAY THROUGH SATURDAY/

Issued at 410 AM MDT Sun May 3 2026

Strong ridging will try to build back into the western US immediately after this storm system. While Wednesday will still feature temperatures well below average for this time of year, expect warmth to recover quickly. Highs around 5F above average can be expected on Thursday, climbing closer to 10F above average by Saturday. Northwest flow will kick up quickly behind the departing trough axis on Wednesday, and lead to breezy to windy conditions. The strongest winds are anticipated on Thursday, when the southeast Wyoming wind prone areas continue to have a 20 to 40% chance for high winds. Both Thursday and Friday will feature isolated to widely scattered PM showers and perhaps a few thunderstorms, but rainfall expectations are limited at best. Precipitation potential will tick up over the weekend a progressive upper level low approaches the area from the northwest. The details concerning this system remain highly uncertain at this lead time.

AVIATION /12Z TAFS THROUGH 12Z MONDAY/

Issued at 523 AM MDT Sun May 3 2026

VFR will prevail through at least midday today. Northwest winds will develop in Wyoming, with gusts to around 25 knots expected mid morning into the afternoon. In Nebraska, winds will be lighter but the direction may move all about the compass through the day today.

Widely scattered showers and isolated thunderstorms are expected to develop this afternoon and continue into the early evening. For terminals along the I-80 corridor, rainfall is unlikely, but these may produce gusty and erratic winds. At BFF, AIA, and CDR, a brief VIS drop cannot be ruled out, but the primary impact will be gusty and erratic winds and occasional lightning. Expect light and occasionally variable winds overnight.

CYS WATCHES/WARNINGS/ADVISORIES

WY...Winter Storm Watch from Monday evening through Wednesday morning for WYZ110-114-116-117. Red Flag Warning from 10 AM this morning to 8 PM MDT this evening for WYZ430-431. NE...None.