textproduct: Grand Junction

KEY MESSAGES

- Wetter weather returns to the region today, with showers and storms possible each day through the end of the work week.

- There is a potential for moderate and heavy rainfall that could lead to flooding mainly in the southern San Juans and surrounding valleys Tuesday through Thursday. A Flood Watch is in effect for SW San Juans and San Juan River Basin including Durango, Bayfield, and Ignacio Wednesday afternoon through Thursday night.

DISCUSSION

Issued at 139 PM MDT Tue Sep 22 2026

Satellite imagery shows a broad high pressure centered over Texas pulling a plume of monsoonal moisture north through Mexico along the Sierra Madre Occidental into the Desert Southwest along the Arizona- New Mexico Border. A trough extending from the Great Basin south to off the Baja Coast is helping to pull that moist plume north. This pattern will dominate the weather for eastern Utah and Western Colorado through the rest of the week and into the weekend, but forecast confidence drops off by the weekend as the models diverge on solutions with some pulling in deeper moisture from the remnants of Hurricane Polo while other models push Polo west into the Pacific keeping the region dry. Stay tuned for updates on this as we go through the week.

Currently a shortwave low is moving north along the Nevada-Utah Border supported by an overhead jet streak across Utah and Western Colorado. This system has been generating thunderstorms across eastern Utah through this morning which are now developing across Western Colorado as the jet streak slides to the east over the region. The 18Z sounding shows a fairly unstable atmosphere above the cool surface layer. Look for storm coverage to increase through the afternoon with diurnal heating under mostly clear to scattered skies. With 50 to 80 mph winds aloft, the primary threat with these storms are damaging winds gusting 60 mph or more. The Storm Prediction Center has northeastern Utah and northwestern Colorado are under a marginal convective outlook for damaging winds associated with the thunderstorms this afternoon and evening. Though pwats arn't so impressive today at 0.79 inches, lightning and brief periods of heavy rain are always threats with passing thunderstorms. Seek shelter if you are outside when These storms roll through; "when thunder roars, go indoors."

Tomorrow through Friday will see an increase of showers and thunderstorms across southwestern Colorado as the southerly flow pushes the moisture up on the southern face of the San Juan Mountains. We have issued a Flood Watch starting a noon tomorrow through 6 AM Friday for zone 19, the southern face of the San Juan Mountains, and for zone 22, the area south to the Colorado-New Mexico Border where 1.50 inches rain or more is possible. If you are in these areas, you should monitor forecast updates and be alert for possible Flood Warnings. Those living in areas prone to flooding should be prepared to take action should flooding develop.

AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/

Issued at 1133 AM MDT Tue Sep 22 2026

Clouds will increase during the afternoon with scattered showers and thunderstorms expected. The main threat with these storms would be gusty winds and heavy rain lowering visibility. PROB30 groups were added to TAF sites to capture the scattered convection through the day. High and mid level clouds will remain over the region overnight with some lowering possible over southern Colorado. VFR conditions are expected though some brief MVFR from a stronger shower or storm can't be ruled out. However, chances for MVFR will increase near daybreak tomorrow.

HYDROLOGY

Issued at 100 PM MDT Mon Sep 22 2026

After a couple days of dry weather, moisture returns today with the deepest moisture expected Wednesday and Thursday, focused across southwest San Juans and southern valleys. Issue a Flood Watch for Wednesday afternoon through Thursday night for SW San Juans and the San Juan River Basin south to the New Mexico Border. This area has seen plenty of rainfall over the last week and remains saturated with the forecast indicating several inches of additional precipitation possible during the Wednesday and Thursday timeframe. Forcing from a robust shortwave will result in multiple rounds of showers and storms with potential for heavy rainfall and flash flooding.

GJT WATCHES/WARNINGS/ADVISORIES

CO...Flood Watch from Wednesday afternoon through late Thursday night for COZ019-022-023. UT...None.