textproduct: Grand Junction

KEY MESSAGES

- Wetter weather returns to the region by Tuesday, 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 Wednesday afternoon through Thursday night.

DISCUSSION

Issued at 1100 PM MDT Mon Sep 21 2026

PRECIPITATION CHANCES RETURN:

After a drier and quiet day yesterday and today (Monday), moisture will make its return as a deeper low pressure trough works into the Great Basin and high pressure sits over Texas, allowing southerly flow to bring up sub-tropical moisture once again. Showers will begin increasing across eastern Utah and the Four Corners as the trough approaches from the west. Showers and storms will increase across western Colorado Tuesday afternoon with scattered storms. A shortwave also moves across northeast Utah into southwest Wyoming with a robust jet streak and our CWA in the right entrance region. So storms that do form Tuesday could be strong given the better shear environment with more localized heavy rainfall possible.

PWATs increase to 180 to 200 percent of normal across SW Colorado by Tuesday evening with the deepest moisture Wednesday and Thursday focused more across SW Colorado. Models seem to indicate a robust shortwave moving through the area overnight Wednesday with a low circulation focused across southeast San Juans and southern valleys, but the SW San Juans and adjacent southern valleys appear to have the best potential for a few inches of precipitation and best forcing. The highest QPF for this round is focusing around the southern San Juans and southern valleys. In fact, there are indications some spots could get several inches, which increases the potential for flooding. Rainfall is possible in the central and northern mountains, but in general the amounts as lower. In coordination with PUB and ABQ, went ahead and issued a Flood Watch for Wednesday afternoon through Thursday night for the SW San Juans (COZ019) and San Juan River Basin (COZ023) where QPF amounts are higher, forcing is better and confidence is higher. This area has also seen plenty of rainfall over the last week with the most recent stretch of moisture so even with two days of dry weather, the ground remains saturated.

Uncertainty increases on whether the moisture gets pushed out of the area or leaves enough to support showers on Friday but some models are indicating another shortwave trough moving through on Friday keeping the weather active. Either way it appears that moisture will not go far so it will not take much to return.

AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/

Issued at 1128 PM MDT Mon Sep 21 2026

Clouds will continue to increase from the southwest overnight bringing few to scattered skies becoming more broken midafternoon onwards. Showers and storms will make an appearance from 21Z onwards with TAF sites either seeing some precip on station or in the vicinity. Heading towards the evening hours, midlevel broken to overcast skies will be the rule. VFR conditions are still expected though MVFR may be reached heading towards the end of the TAF period.

HYDROLOGY

Issued at 1100 PM MDT Mon Sep 21 2026

After a couple days of dry weather, moisture returns Tuesday with the deepest moisture expected Wednesday and Thursday, focused across southwest San Juans and southern valleys. Decided to issue a Flood Watch Wednesday afternoon through Thursday night for SW San Juans and San Juan River Basin. 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 Thursday evening for COZ019-023. UT...None.