textproduct: Cheyenne

KEY MESSAGES

- Another round of accumulating snow is expected Thursday evening into Friday night. Considerable uncertainty remains regarding forecast snow totals.

- Two scenarios for the evolution of the storm system remain possible, which would lead to significantly different outcomes for our area.

- Gusty winds are expected Friday in the wake of a cold front. This will lead to blowing snow concerns in areas receiving snow Thursday night and Friday.

- The pattern will shift to mostly dry and above normal temperatures after Saturday and persist through the start of next week with high winds possible during this time as well.

SHORT TERM /THROUGH FRIDAY NIGHT/

Issued at 400 PM MST Wed Mar 4 2026

The primary forecast challenge today is the potential for snow accumulation on Thursday night into Friday. First, we have another warm day to get through before winter returns. Currently, we have mainly clear skies in place over the area with mild temperatures in place once again. Winds are pleasantly light for most areas aside from a few modest breezes. Cloud cover associated with the next storm system is already apparent on GOES satellite imagery moving into the western CONUS this afternoon. A north to south band of mid to high level cloud cover is out ahead of the primary trough axis. This will push in late this evening and lead to a cloudy start to Thursday morning especially along and east of the Laramie Range. Expect a window of sunnier skies in the late morning to early afternoon hours as the dry-slot moves overhead, before cloud cover increases again in the late afternoon hours Thursday. Temperatures will be quite warm once again Thursday, mainly east of the Laramie Range, with southwest flow aloft supporting strong warm air advection ahead of the approach upper level low. 700-mb temperatures in the 0 to +3C range over the High Plains, supporting widespread 60s and maybe a chance at 70 degrees in some lower elevation areas.

Thursday evening, attention will shift to the potential for snow. We will start off here with an overview and then get into the details and scenarios for snow accumulation outcomes. We may see a few elevated showers developing late Thursday afternoon and evening, but these will be on top of very dry boundary layers, so anything reaching the ground is fairly unlikely. The surface cold front is expected to move through the area in two phases. During the day on Thursday, an elongated surface trough will develop just east of the I-25 corridor. So, while an initial push of cool air will move in Thursday morning, this is expected to stall west of I-25 during most of the day. By the evening hours, the secondary surface low over northeast Wyoming will begin to cede to a stronger developing surface cyclone in northeast Colorado. As this happens, expect a second push of cooler air to sweep through the High Plains, with gusty north to northwest winds moving in behind. This will make for a dynamic evening as strong frontogenesis sweeps through the area moving into the developing cyclone. In addition, we will have steep lapse rates and some modest instability present, possibly locally enhancing precipitation rates. Initially, snow levels will be around 7500 ft, so precipitation may be rain to begin with. However, expect this to change quickly over to snow at least for areas above about 6000 ft. Cold air advection overnight into Friday morning will continue to drop snow levels, and we should be seeing mainly snow by daybreak. Gusty north winds will fill in over most of the area by Friday morning as well, which will at least be producing some colder wind chills, and possibly leading to areas of blowing and drifting snow depending on how much falls. On that subject, let's get into the details on a pretty uncertain forecast below.

Models have diverged into two distinct camps today, each leading to wildly different outcomes for our area. The deterministic GFS and deterministic ECMWF are fairly representative for each camp. The first scenario represented by the GFS depicts a stronger upper level low positioned slightly further north, while the second scenario represented by the ECMWF shows a weaker upper level low positioned slightly further south. The overall synoptic set up will be a split trough moving across the area, with a parent trough well to our north over the US/Canada border, and a second upper level low moving across the central Rockies. The key differences are in the strength of this second upper level low. The more aggressive GFS scenario deepens this low enough to close it off and distinctly separate the system from the parent trough. This allows easterly flow in the 700 to 500-mb layer to develop over our area by Friday morning, funneling in good moisture and very strong isentropic lift into our area. A TROWAL backing into the area will support strong lift through much of the day Friday and widespread accumulating snowfall over the High Plains. In the ECMWF scenario, the secondary upper level low is slightly weaker, and thus does not close off from the parent trough. Remaining as an open wave, easterly flow is prevented with deeper moisture deflected off to the north and east towards the parent trough. Without the easterly flow and moisture tap, the window for precipitation is much shorter, likely ending Friday midday or so. Precipitation rates would also be lighter and primarily driven by frontogenesis, since the strong positive theta-e advection and isentropic lift would be lacking. It is difficult to favor one scenario over the other at this time. Nearly all GEFS members are very much in line with the deterministic GFS, whereas nearly all ECMWF ensemble members are close to their deterministic run. The Canadian ensemble suite is a little closer to the ECMWF camp, while AI ensemble systems generally lie somewhere in between. This event is near the tail end of the usefulness of high resolution models still, but those are equally divergent, with the HRRR showing a solution roughly in between the two scenarios, and the 3km NAM as an extreme outlier with little to no precipitation for the majority of the area.

Taken all together, the divergence between model scenarios leads to a fairly low confidence forecast today. The official forecast generally splits the difference between the two most likely scenarios, but we have a huge spread between the 10th and 90th percentiles. At this time, the highest confidence in some snow impacts is generally inside an Elk Mountain to Wheatland to Cheyenne triangle. In this area, the most likely snowfall range is around 3 to 6 inches, but the high end scenario could be as much as 8 to 10 inches. Northerly surface winds are good for accumulating snowfall in the Elk Mountain to Laramie corridor, including the city of Laramie, then extending eastward to just north of Cheyenne up towards Chugwater. The Pine Ridge area from Douglas towards Chadron can also do well in northerly flow, but the western part of that area may be on the edge of the moisture, while the eastern part may have issues with precipitation type and snow melting upon reaching the ground due to warm temperatures. For today's update, decided to focus on headlines along and west of the Laramie range, and will leave the I-25 corridor and points east to later shifts. The highest probability for warning criteria snow amounts is in the southern Laramie Range where a Winter Storm Watch has been issued. In adjacent areas including the I-80 corridor from Elk Mountain to Laramie and the central Laramie Range, the probability for warning criteria amounts is about 30 to 40% at this time, which is a little lower than we would like to see for a watch. Opted to issue a Winter Weather Advisory for this area, but there is a notable chance this may need to be upgraded to a Winter Storm Warning if the higher end scenario becomes favored. A Winter Weather Advisory was also issued for much of Carbon County, but this will be a more marginal advisory compared to areas further east. This may also need to be expanded into the Saratoga and Baggs areas, but did not have the confidence to do so at this time. We will also need to expand headlines eastward, but the start time will be a little later there so will wait a bit longer for confidence to improve.

The different scenarios have also differ in the end time of precipitation, but we should be done by around midnight Friday night even in the high end scenario. Warm air advection will return for the weekend behind this storm system.

LONG TERM /SATURDAY THROUGH WEDNESDAY/

Issued at 400 PM MST Wed Mar 4 2026

At the start of the long term, a benign weather pattern will settle in across the region as a system that impacted our CWA the day prior exits off to the east. As we progress through Monday, we dry out and remain dry as precipitation chances are minimal with the upper-level pattern becoming zonal. Then, a pattern change is possible Tuesday as a shortwave drops south, increasing precipitation chances and leading to cooler temperatures, more on that later. As of now, most of the precipitation associated with this system should remain all rain at lower elevations and snow in the higher terrain. There maybe a short window of the rain transitioning to snow Tuesday night, but at this time there should be minimal to no snow accumulations at the lower elevations. Now, lets take a look at temperatures, with a fresh blanket of snow across the CWA, expect slightly cooler temperatures to continue into Saturday. Thereafter, a warming trend will ensue Sunday as 700mb temps increase into the 2 to 4 degree C range. These temperatures will remain in place through Monday, then with a front diving south Tuesday, cooler temperatures will once again make a return. So, we don't live at 700mb, what does this all mean at the surface? Well, expect highs to climb into the mid 30s west of I-25 and 40s to low 50s east of the corridor on Saturday. Temperatures will warm Sunday into Monday as highs soar into the upper 40s to low 50s west of I-25 and low to upper 60s to the east, warmest across the Nebraska Panhandle. By Tuesday, a cooling trend will round out the long term period.

Switching to winds, expect windier conditions to make a return to our wind prones across southeast Wyoming Sunday through Wednesday. A 700mb jet will dive south, increasing mid-level winds to near 65 knots Sunday afternoon/evening. These winds will mix down to the surface as sinking air aloft sets up, negative Omega (GFS). There will be some variance in strength through Wednesday, but expect the windy conditions to continue from Sunday. All this coupled with our in-house guidance, there is a 80% chance of high winds along I-80 near Arlington late Saturday though Sunday night and along I-25 at Bordeaux. High wind probabilities decrease through the remainder of the forecast period. As of now, in-house guidance has probabilities of high winds in Cheyenne generally less than 20% for the aforementioned duration.

AVIATION /06Z TAFS THROUGH 06Z FRIDAY/

Issued at 1050 PM MST Wed Mar 4 2026

Quiet weather expected over the next 18 to 24 hours with low Aviation impacts. The next Pacific storm system and associated cold front will move into Wyoming late Thursday afternoon and evening, with winds shifting more out of the north or northwest.

HAZARDS/WEATHER TRENDS: VFR conditions will prevail over the next 24 hours. The leading edge of the colder air will move into KRWL, KLAR, and KCYS after 19z, with winds shifting into the northwest. Gusts between 20 to 30 knots possible for mainly KRWL and KCYS.

CYS WATCHES/WARNINGS/ADVISORIES

WY...Winter Weather Advisory from 8 PM Thursday to midnight MST Friday night for WYZ103-106-110-112-114-115. Winter Weather Advisory from 8 PM Thursday to 6 PM MST Friday for WYZ104-109. Winter Storm Watch from Thursday evening through Friday evening for WYZ116-117. NE...None.