textproduct: Grand Junction

KEY MESSAGES

- Showers and storms will continue this week each afternoon and evening. The greatest coverage will be on Wednesday. - Primary threats include heavy rainfall, lightning, and outflow winds up to 30-50 mph. Hail cannot be ruled out in stronger storms.

- Storms have the ability to produce flash flooding and debris flows in vulnerable terrain, including areas near and downstream of burn scars.

UPDATE

Issued at 130 AM MDT Wed Jul 22 2026

After several days of heavy rainfall rates and reports of flash flooding and debris flows have decided to hoist a Flash Flood Watch for all of eastern Utah and western Colorado today into this evening. The peak of anomalous moisture occurs today along with a passing wave to tap into the moderate instability in place. Expect storms to continue to produce rainfall rates in excess of 1-2 inches per hour with burn scars especially vulnerable. Models are still scouring out much of the convective debris clouds through late morning. The eastern AZ wave arrives at peak heating to help release the instability and produce scattered to widespread convection. Storms today take on a bit more northerly track which could also help it align on terrain which has been sheltered in the E/SE flow the past few days.

DISCUSSION

Issued at 950 PM MDT Tue Jul 21 2026

The main concern over the next 24-48 hours will be a weak shortwave tracking over portions of the area. The moisture we have in place is already modest, but the wave is going to bring a slight uptick (PWAT 175-215 percent of normal). It will also supply some lift to aid convective development, which should translate to widespread coverage. The 00z GJT sounding revealed steep midlevel lapse and those will still be in place tomorrow. The lapse rates and moisture combo should result in CAPE around 1000 j/kg. Given this environment storms tomorrow will be capable of producing strong winds, hail and heavy rainfall. The heavy rain may result in flash flooding and debris flows especially around steep terrain and recent burn scars. This potential is for most locations across the area. Many spots have been getting heavy rainfall the past several days, which has lead to saturated soils. This further increases the potential for excessive runoff. If this increased moisture leads to expansive cloud cover that lingers through mid day tomorrow then the atmosphere will not be as unstable. This could ultimately cause a decrease in coverage and intensity of storms. Therefore held off on issuing a flash flood watch, but it is certainly possible especially if the skies are clear in late morning. Models show the shortwave trough still tracking overhead Wednesday night. This could support showers and storms continuing overnight. Although by late evening the rainfall rates should be on the decrease.

On Thursday the trough crosses the Divide at some point leaving behind westerly flow. Plenty of moisture will still be around for peak heating, so it looks like terrain-driven storms are likely in the afternoon. Despite some dry air behind the wave the moisture values still support the potential for heavy rainfall. On Friday northwest flow will be in place and models hint at dry air trying to filter into the area. When that happens is a pretty good bet the coverage decreases. Although low level moisture is usually slow to filter out, so it should support another round of terrain-driven storms in the afternoon. Behind that the confidence lowers as models are not sure how to handle the pool of moisture. How far south does it go and when will return flow bring it back into the area? Is there enough lingering moisture to keep orographic showers going into the weekend? Stay tuned

AVIATION /06Z TAFS THROUGH 06Z THURSDAY/

Issued at 1132 PM MDT Tue Jul 21 2026

Scattered showers with embedded thunderstorms continue to drift across much of the region late this evening. Light rain and a nearby thunderstorm are impacting several TAF sites but VFR remains. Lingering convective debris clouds will persist through sunrise with cigs at or above 120kft agl. Another active day and overnight is forecast for Wednesday into Thursday. VFR is prevailing in TAF sites with ILS possible in the PROB30 groups at some sites. Confidence not high enough for MVFR or below attm but if a heavy rain shower moves over the airfield this is very possible over the next 24 to 36 hours.

HYDROLOGY

Issued at 1148 AM MDT Tue Jul 21 2026

A rich plume of monsoonal moisture has become established across portions of eastern Utah and western Colorado. Scattered thunderstorms capable of producing heavy rain are expected to continue this afternoon into late evening hours. Rainfall rates of 2- 3 inches per hour will be possible with the stronger storms. These rates could lead to flash flooding and debris flows especially over steep terrain and recent burn scars. Also, rain over the past several days has lead to saturated soils, which increase the chances for excessive runoff.

As a reminder: Keep an eye on our forecasts through the end of the week and stay tuned for updated hydrology alerts if visiting or if you reside below terrain vulnerable to flash flooding and/or debris flows. Dry creeks and arroyos can fill quickly and without warning from storms miles away.

GJT WATCHES/WARNINGS/ADVISORIES

CO...Flood Watch from 11 AM MDT this morning through late tonight for COZ001>014-017>023. UT...Flood Watch from 11 AM MDT this morning through late tonight for UTZ022>025-027>029.