Area Forecast Discussion

KEY MESSAGES

- Showers and thunderstorms expected over the plains tonight and tomorrow, with some strong to severe possible east of I-25.

- Cooler Monday, then gradual warming trend through the remainder of the week as moisture returns to the higher terrain and southern border.

SHORT TERM /THROUGH SUNDAY NIGHT/

Issued at 136 PM MDT Sat Sep 19 2026

Currently...Upper low pressure system centered over southern ID is producing deep southwest flow across the Four Corners, drawing up moisture into Colorado. Some convection has fired over the higher terrain as of 1 PM but nothing too strong just yet. Temps as of 1 PM have warmed into the 70s to lower 80s for the plains, and mid 60s to lower 70s for the high valleys.

Tonight...The upper low to the north will push east into WY tonight, shifting the flow aloft to a more westerly direction which should start drying out the higher elevations. At the same time, a cold front is forecast to drop south across the Palmer Divide right in the 4 PM to 6 PM time frame. SPC has painted a good portion of the far eastern plains within a Slight chance for severe storms, keying in on the 1500-1800 j/kg of CAPE and 40 kts of 0-6 km bulk shear. However, this favorable area for strong to severe storms quickly pushes south as the front moves in, so best chances for heftier storms this eve will be 4-10 PM, with a focus closer to the KS border. Main threats will be gusty outflow winds to 60 mph, 1 inch hail and periods of moderate to heavy rainfall. Further west along the I-25 Corridor, feel that convection will not be as structured and pose a strong wind gust threat through 6 or 7 PM. Plan on overnight low temps tonight in the mid 30s to mid 40s for the high valleys, and upper 40s to mid 50s for the plains.

Sunday...Another active day expected as the low to the north continues pushing east, reaching Nebraska and South Dakota by the afternoon. A couple of things to keep in mind - first, this is a post-frontal day with a healthy amount of llvl moisture to work with across the eastern plains. Model CAPE is ranging from 1500-2000 j/kg across the eastern plains by midday. Second, as the northern low continues moving east, it will force another cold front south that will provide an increasing amount of bulk shear through the afternoon, with some models showing 45-55 kts right along the Palmer Divide. Given this combination, SPC has moved the Slight chance for severe storms down into much of the eastern plains. Convection will likely initiate over Monument Hill and along the Palmer Divide around 1 PM, then gradually spread in areal coverage and intensity through the mid to late afternoon, with activity lingering over the far eastern plains late into the night. As for temps. look for highs in the 70s for the high valleys, and 70s to around 80F for the plains. Overnight lows will cool into the mid 30s to lower 40s for the high valleys, and mid 40s to mid 50s for the plains.

LONG TERM /MONDAY THROUGH FRIDAY/

Issued at 136 PM MDT Sat Sep 19 2026

Monday and Tuesday...With the northern low out of the region, temporary ridging develops across the Four Corners region as another Pacific low moves onshore across southern CA and southern NV. Both Mon and Tue are the coolest days out of the extended period, with high temps failing to hit 80F. Increasing southwest flow aloft will mean a gradual return and moisture to the mts by Tue, but for Mon dry conditions will persist for the higher terrain, while the eastern plains will see some late afternoon and evening convection.

Wednesday through Friday...A lot of variability with the extended solutions, though long range models do seem to agree that the Pacific low ejects to the northeast across the Great Basin on Wed, boosting temps slightly due to the increased southwest flow as well as increasing precip chances for the mts and southern border. Beyond that, NBM indicates stabilizing temps right around seasonal normals, and a daily chance of showers and thunderstorms, more heavily weighted towards the mts and the southern border.

AVIATION /18Z TAFS THROUGH 18Z SUNDAY/

Issued at 1135 AM MDT Sat Sep 19 2026

Upper low over ID will push east in WY this evening, continuing moist southwest flow across the Four Corners and into CO. It will also force a cold front south across the eastern CO plains this evening which will be instrumental in developing convection across the Palmer Divide and eastern plains tonight. Otherwise, VFR conditions are anticipated for much of the forecast area over the next 24 hrs, including the three main TAF sites of KCOS, KPUB and KALS.

KCOS and KPUB: Have PROB30 for -TSRA between 21z and 03z in the TAF as well as variable gusts to 35 kts.

KALS: SW winds gusting to 25 kts today between 20z and 01z. There will be some convection over the surrounding higher terrain, but confidence is low that it will cross terminal so did not mention.

PUB WATCHES / WARNINGS / ADVISORIES

None.