Area Forecast Discussion

KEY MESSAGES

- Cold front this morning with cooler temperatures this afternoon. Thunderstorms look to remain confined to the higher terrain.

- Multiple waves Wednesday through Friday will combine with abundant moisture to produce thunderstorms with heavy rain, especially for the southern Mountains.

- Some uncertainty for the weekend into early next week with the pattern evolution.

SHORT TERM /THROUGH TONIGHT/

Issued at 1235 AM MDT Tue Sep 15 2026

Currently...satellite imagery shows widespread cloud cover across southern Colorado early this morning in persistent southwest flow. Radar shows light rain showers across the Continental Divide which will continue through much of the early morning hours. Temperatures are currently in the 60s across the Plains. A cold front is forecast to drop south across the Plains early this morning, with gusty north winds 20 to 30 mph forecast through daybreak. This will bring cooler temperatures by morning with most areas on the Plains in the 50s to low 60s. There could be some patchy fog across the San Luis Valley through morning.

Today and tonight...the cold front will travel south across the Plains this morning with northerly flow shifting southeast by this afternoon. Moisture will slowly increase with dewpoints in the 50s expected by this evening. Temperatures will be cooler, with mainly 70s across the Plains and San Luis Valley. Instability looks to be limited today, with less than 500 j/kg across the higher terrain. Expect showers and thunderstorms to remain confined to the Continental Divide, with more isolated to scattered activity by late afternoon to early evening over the Eastern Mountains. Lack of instability on the Plains should help limit shower and thunderstorm activity, keeping areas east of I-25 dry. Lightning, brief heavy rainfall and wind gusts near 40 mph may accompany any stronger storms over the higher terrain. Overnight lows tonight will fall into the 50s across the Plains and 40s for the San Luis Valley.

LONG TERM /WEDNESDAY THROUGH MONDAY/

Issued at 1235 AM MDT Tue Sep 15 2026

Models in good agreement through Friday, with differences showing up for the weekend into early next week. Active weather is expected for mid to late week, with uncertainty heading into the weekend and early next week.

Wednesday through Friday...an upper low will slowly shift east out of the Pacific Northwest, while upper high pressure sits across the southeast states. This will put southern Colorado under south to southwesterly flow, with multiple upper wave moving north across the state. PWAT values increase significantly to in excess of 1 inch, while dewpoints remain elevated in the 50s and lower 60s across the region. All point to efficient rain producing thunderstorms across the higher terrain. The main vort max train runs from Arizona, northeast into northeast Colorado, with areas over the higher terrain, Palmer Divide and Raton Mesa favored. Issued a Flash Flood Watch for the eastern San Juan Mountains and upper Rio Grande Valley for Wednesday afternoon through Thursday evening. The first upper wave will lift north Wednesday afternoon and evening, with periods of heavy rain expected across the Colorado Mountains. A brief lull is expected Thursday morning, before another upper wave lifts into the southwest portion of the state Thursday afternoon. This will lead to another round of heavy rain producing thunderstorms. Further east, showers and thunderstorms are expected, both Wednesday and Thursday afternoon and evenings, favoring the Palmer Divide and Raton Mesa. Models differ on how far east to track thunderstorms, but they could shift off the higher terrain and impact portions of the Plains through the overnight hours. Flash flooding may be possible on area burn scars and a watch may be needed.

The upper low tracks eastward into the Northern Rockies on Friday shifting the main vort max feed east into eastern Colorado. This will likely be the best chances for areas on the Plains to see shower and thunderstorm activity. Mountain areas will continue to see periods of heavy rainfall on Friday, with a continued flash flood risk.

Temperatures look to remain cooler, with 70s and 80s each afternoon Wednesday through Friday. Overnight lows will fall into the 50s and 60s across the Plains.

Saturday through Tuesday...there is a high degree of spread among the deterministic guidance and ensembles heading into the weekend and early next week. The GFS remains activity with a quick moving upper ridge over the weekend, followed by another upper wave tracking across Colorado early next week. The GFS would dry southern Colorado out over the weekend, with a return to wet conditions early next week. The ECMWF and Canadian are similar to the GFS with an upper ridge for the weekend, but differ by early next week, with a broad trough out west and southwesterly flow across Colorado. Overall, drier and warmer weather is forecast for the weekend, with active weather heading into early next week with the GFS the wettest guidance compared to the ECMWF and Canadian.

AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/

Issued at 1051 PM MDT Mon Sep 14 2026

A cold front will move across the eastern plains overnight, bringing gusty north winds of 20-35kts to COS and PUB by 10-12Z. Winds gradually become south to southeast 15-25kts through the late morning and afternoon along with VFR cigs. Currently looks too stable for convection at COS and PUB through the taf period, though will need to watch for possible outflow boundaries from mountain storms.

Clearing skies and light winds at ALS this evening could lead to IFR fog developing early Tuesday morning, however, there is not enough confidence to include more than VCFG at this time. Breezy southerly winds develop aft 18Z with PROB30 for storms at the terminal through the late afternoon and evening.

PUB WATCHES / WARNINGS / ADVISORIES

Flood Watch from Wednesday afternoon through Thursday evening for COZ067-068.