textproduct: Grand Junction

KEY MESSAGES

- Showers and storms will continue this week each afternoon and evening, with coverage becoming more widespread by Tuesday and Wednesday.

- Primary threats include heavy rainfall, lightning, and outflow winds (30-40 mph). Some small hail will also be possible.

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

DISCUSSION

Issued at 1018 PM MDT Mon Jul 20 2026

Little change in the synoptic pattern is expected Tuesday with high pressure parked over the Great Basin. However, a few mesoscale developments will prove pivotal to the forecast. Monsoonal moisture will continue to trickle beneath the high Tuesday afternoon. Height falls produced by weak shortwaves will initiate a shift southeast of the high. In the meantime, this shortwave energy will engage the existing moisture pool and produce another afternoon of convective showers and thunderstorms. Storms Monday evening were producing rainfall rates of 1-2 inches per hour in places, enough for numerous flash flood warnings on susceptible burn scars and flood prone terrain. There's reasonable confidence precipitation becomes more widespread with additional dynamic forcing from the shortwaves. This should increase storm half- life appreciably over the next couple of days. Thereby, increasing the likelihood of more flash flooding and hydrological concern on burn scars. Storm motions will stay slightly eccentric on Tuesday favoring east to west motions once again.

By midweek, the high-pressure system will shift slightly, altering our storm tracks. While storms have recently been taking an unusual east-to-west path, the new pattern will likely steer them up from the south and perhaps the west by late week. After that shortwave passes to our north westerly flow becomes established. This may alter the moisture across the area, which in turn may change daily storm chances.

As far as temperatures are concerned, daytime highs will continue to be above normal for the next few days, with near normal temperatures expected Wednesday and beyond.

A special note for outdoor enthusiasts: Please continue to monitor the forecast and adjust your plans as needed. These storms can develop rapidly, bringing sudden hazards. Your best bet is to head out early in the morning, as storm activity typically strengthens in the afternoon. Always ensure you have multiple ways to receive weather warnings.

AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/

Issued at 1138 PM MDT Mon Jul 20 2026

Showers with embedded thunderstorms continue to drift westward across the state line into eastern Utah late this evening. Most TAF sites are clear of this threat with lingering convective debris clouds leaving cigs at or above 120kft agl. KCNY could see some light showers linger past midnight. Plenty of moisture and instability remains for another active afternoon and evening expected to impact most TAF sites with the threat of a passing thunderstorm well into the early morning hours of Wednesday. 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 1018 PM MDT Mon Jul 20 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 Tuesday. Rainfall rates of 1-2 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...None. UT...None.