textproduct: Grand Junction

KEY MESSAGES

- There is a chance for strong storms over the next few days, capable of producing hail, gusty winds, and heavy rainfall.

- Moderate to heavy rainfall could lead to localized flash flooding, rockfalls, and mudslides at times this week.

- Temperatures run near to around 5 degrees below normal through the end of the week.

DISCUSSION

Issued at 1032 PM MDT Mon Sep 14 2026

High pressure remains in place over the Southeast, with troughing over the West Coast. This will keep moist southwesterly flow in place through the end of the week, maintaining an anomalously rich moisture pool over eastern Utah and western Colorado. PWATs will hover around 200% of normal for mid-September through the end of the week. This equates to PWAT values around 1.00 inches, which is more than enough to produce heavy rain. The Weather Prediction Center keeps a marginal risk of excessive rain across most of eastern Utah and western Colorado through at least Friday, with a slight risk of excessive rain outlooked for areas around the Four Corners through Thursday. As a result, the highest likelihood of flash flooding, debris flows, and rockfalls will be for areas south of the I-70 corridor, with lower chances across the north.

An upper level jet lingers over the Four Corners through Thursday, providing some dynamic forcing and adding some wind shear. Where enough instability is present, this could result in strong to severe thunderstorms, capable of producing large hail and damaging winds. The question, as always, becomes whether or not morning cloud cover will hamper afternoon convection chances. Hi-Res models remain bullish on afternoon instability values Tuesday, with 1000-1500 J/kg of CAPE south of I-70, and 500-1000 J/kg of CAPE elsewhere. As a result, we could see similar activity to that earlier today. Wednesday is set up to be the big day at this point, with the best moisture of the week, jet energy still in place, and a shortwave transiting the region. There is potential for widespread heavy rain as a result, though the details will have to wait until the higher resolution model data comes in.

Models indicate the upper level West Coast trough starting to push east on Thursday, nudging the moisture plume eastward. This will lead to a slight downturn in convection Thursday afternoon, but with plenty of surface based moisture still around, it will likely be another rinse and repeat day of widespread afternoon showers and thunderstorms. Friday onward, forecast confidence decreases. Models are in poor agreement as to what happens once the West Coast trough ejects to the northeast, with some solutions building a ridge, and others developing a Rex Block over the Southwest. Ensembles do indicate a gradual drying trend, but keep PWATs of 100-150% of normal around through the weekend. That's enough to keep a chance of at least an isolated, terrain based shower or storm in the forecast. With abundant cloud cover and shower activity expected through the end of the week, temperatures will run near to around 5 degrees below normal.

AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/

Issued at 1141 AM MDT Tue Sep 15 2026

Showers and thunderstorms are expected to develop during the afternoon. TEMPO groups were added for most sites with the main threats being locally heavy rain reducing visibility along with gusty winds. Lesser coverage of showers and storms are expected overnight with PROB30 groups included in most groups. This active pattern will continue for the 24 hour period. MVFR and IFR conditions will be likely in showers and thunderstorms.

GJT WATCHES/WARNINGS/ADVISORIES

CO...Flood Watch from Wednesday afternoon through Thursday evening for COZ018-019-021>023. UT...None.