textproduct: Cheyenne

KEY MESSAGES

- Temperatures warm on Sunday and Monday with increasing precipitation chances.

- Severe weather chances return on Sunday, with Monday seeing a potential critical fire weather environment alongside high winds.

- Much cooler on Tuesday with temperatures a few degrees warmer through the end of next week and daily chances of showers and thunderstorms.

SHORT TERM /THROUGH MONDAY NIGHT/

Issued at 250 AM MDT Sun Sep 13 2026

The pattern through Monday will consist of an upper level transient ridge today that will give way to a Pacific low moving across the US/Canada border with attending troughing overspreading our region through Monday before departing. At the surface, a stalled frontal boundary will lift as a warm front today and move out of the region, with a secondary cold front then dropping down through Monday. This should create an eventful end to the weekend and an accompanying busy day to start the work week as well. For Sunday, scattered shower and thunderstorm development from surging moisture and the forcing provided by the incoming system and frontal boundary is expected. While the last several days model runs haven't been as excited for severe development, latest guidance is starting to pick back up on the potential for scattered severe thunderstorm development. Initially steep lapse rates with increasing instability and an evening low level jet fueling wind shear should allow for the potential for severe thunderstorms, however convective inhibition may still prevent stronger storms. Nonetheless high resolution guidance shows some destabilization during the late afternoon into the evening, and a few storms capable of damaging winds and large hail could be possible. Otherwise it'll be a warm day, with daytime highs in the upper 70's to upper 80's.

Moving into Monday, focus shifts off of showers and thunderstorms and back to fire weather conditions and high winds. Winds at 700mb are around 40-50 knots during the day due to the passing system, and Craig to Casper pressure gradients of 50+ meters are expected to produce widespread wind gusts of 40-50 mph, with our usual wind prones potential reaching 55-60 mph for the day. While in house guidance remains generally unconvinced with the probability of 58+ mph gusts at only around 40%, seeing enough potential in high resolution guidance that a High Wind Watch was issued for Rawlins, Arlington, and Bordeaux zones (the usual suspects). And as drier surface air moves into the region and daytime relative humidities drop to the teens, critical fire weather conditions will return as well for a good portion of southeast Wyoming. Fire Weather Watches have also been issued for Monday in response to this. A few showers or storms will also be possible on the day, but these should be mostly relegated to the I-80 corridor and southwards, with minimal to nil stronger activity anticipated. Prior to the front look for similar temperatures to Sunday with 70's to 80's expected, but rapidly cooling thereafter leading to a much cooler Tuesday.

LONG TERM /TUESDAY THROUGH SATURDAY/

Issued at 156 PM MDT Sat Sep 12 2026

Active weather is expected for much of the upcoming week with multiple upper-level disturbances pushing through the region. Monday features the strongest disturbance expected for the week as a stout upper-level trough digs across Montana with a 100kt jet along the southeastern portion. The jet will move eastward with the upper- level low, placing the CWA within the right entrance region of the upper-level jet for much of the day Monday. Enhanced, dynamically- driven ascent will provide much needed forcing for showers and thunderstorms Monday morning and afternoon. Multiple 500mb vorticity maxima will eject across the area as the upper-level low moves eastward, favoring addition forcing across much of the region. The 700mb low is expected to be displaced to the north across the southern Saskatchewan Province. While this low will be displaced to the north, it looks to be quite strong, with an associated jet around 50 to 60kts over the Northern Plains. For Southeast Wyoming and Western Nebraska, the low will lead to strong, westerly flow across the CWA around 40 to 45kts Monday morning. If you have lived in this area for a while now, you may know where this is heading... The surface low with this system will dive southeastward from the Black Hills towards central Nebraska, with a strong, trailing cold front. This low progression is favorable for strong, west to east surface pressure gradients to develop across western portions of the area and across the Laramie Range. The surface pressure gradient across the Laramie Range peaks around 2 to 3mb Monday morning. GFS Omega field suggest modest to strong downward motion along the Laramie Range and just east. With all these factors considered, Monday morning will likely see very strong winds across much of the region, though a High Wind Warning is currently not anticipated, but this may change as this event moves into the short term. In-house random forest model guidance is giving around a 30 to 40% chance for high winds at Arlington, Rawlins, Bordeaux, Coleman, and northern Carbon County. Therefore, high wind criteria winds cannot be completely ruled out at this time and this setup will need to be monitored closely as Monday morning approaches.

In addition to the potential for strong to near-high wind criteria winds, this system will bring a strong cold front to the region, dropping temperatures from the low-70s to upper-80s on Monday into the upper-60s to mid-70s on Tuesday. Most locations east of the Laramie Range will be around 10 to 12 degrees cooler on Tuesday. Additionally, isolated to scattered showers will be possible Monday with the front moving through, resulting in low-level forcing for ascent. Dewpoints in the 50s and 60s east of the Laramie Range on Monday will favor precipitation development with the front, before dewpoints tank into the 30s and 40s behind the front. With the frontal passage timing, precipitation will be largely confined to the I-80s corridor across the region. The long range models currently suggest that some CAPE may be present across the region Monday morning and afternoon, so an isolated storm or two cannot be ruled out especially across the southern Panhandle.

After the cold front Monday, temperatures will remain quite nice through the remainder of the week, likely staying in the 60s and 70s with a couple of low-80s possible Wednesday. Daily precipitation chances are expected as the upper-level flow remains more dynamic than it has been in the past several weeks.

AVIATION /12Z TAFS THROUGH 12Z MONDAY/

Issued at 532 AM MDT Sun Sep 13 2026

VFR conditions expected through the next 12 hours or so. Thereafter, increasing showers and thunderstorms will bring brief periods of lowered VIS alongside generally mid level CIGs. Overnight into tomorrow morning showers continue to be possible across most sites with lowering CIGs for western Nebraska terminals. Have left KBFF out of this for now based on latest guidance, but otherwise all other NE terminals can expect the potential for IFR conditions or lower. Strong winds, gusting 25-35 knots with locally higher and erratic gusts from nearby thunderstorms. LLWS also expected for KBFF overnight.

CYS WATCHES/WARNINGS/ADVISORIES

WY...Fire Weather Watch from Monday afternoon through Monday evening for WYZ418>422-432-433. High Wind Watch from Monday morning through Monday afternoon for WYZ106-109-110. NE...None.