textproduct: Grand Junction

KEY MESSAGES

- Showers and thunderstorms will continue each afternoon and evening through at least early next week.

- Main threats with these storms include lightning, localized heavy rainfall, and gusty outflow winds (35-45 mph).

- These 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 1012 AM MDT Sat Jul 18 2026

The current upper level pattern is characterized by a stagnant high pressure system. This will lead to many rinse and repeat days when it comes to the forecast. Current guidance continues to suggest PWAT values around 150-200% of normal for the next few days. This will be enough moisture to support daily showers and thunderstorms each afternoon and evening through the weekend for the CWA. It is also becoming more possible that we hold onto this moisture into early next week as well. A system moving along the US/Canada border will cause the high to pivot allowing moisture to fill in across the northern CWA, which has been relatively quiet. By mid next week the flow shifts to more a more southerly and possibly westerly direction. The will change the evolution of afternoon convection compared to the last several days.

A majority of these daily storms will initialize over the higher terrain before spreading through the valleys as outflows develop. Additional storm development is also possible where these outflows collide with each other and the higher terrain. The primary threats with these storms include lightning and heavy rain, in addition to small hail and gusty outflow winds (35-45 mph). Although we welcome much of this rainfall with open arms, localized heavy rainfall could result in flash flooding and debris flows. This is especially of concern over highly sensitive areas like recent burn scars. The hydrology section below discusses the risk in greater detail.

As previously mentioned, these storms have the ability to pop up rather quickly, so be sure to monitor the forecast and have multiple ways to receive weather alerts. This is especially important if you are visiting or reside below terrain that is vulnerable to flash flooding.

AVIATION /18Z TAFS THROUGH 18Z SUNDAY/

Issued at 1012 AM MDT Sat Jul 18 2026

VFR cigs and vsby are expected to remain across most of western CO and eastern UT TAF sites through the forecast period, except periods of MVFR cigs/IFR vsby in and around thunderstorms. Showers and isolated storms will continue to expand in areal coverage thru the aftn. Convection today, is expected to diminish in a similar fashion to yesterday, trending more twd stratified showers btwn 02Z and 04z. The main threats with convection will be lightning, gusty outflow winds (30-45kts), and brief periods of heavy rainfall.

HYDROLOGY

Issued at 1012 AM MDT Sat Jul 18 2026

Anomalous moisture has become established across portions of eastern Utah and western Colorado. 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 recent burn scars.

Storms over the last few days have helped prime lower levels of the atmosphere and saturate the ground where rain was observed. Several locations across southwest Colorado have reported 0.5 to 1.0 inches of rain within 30 minutes; which is more than sufficient to create issues in our steep, rocky terrain that is already susceptible to flash flooding. This environment also triggers heightened awareness over recent (or actively burning) fires, due to the burnt ground's inability of absorbing moisture under heavy rainfall. As such, we continue to emphasize the potential for flash flooding and debris flows in this regime.

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 vulnerable terrain to flash flooding and/or debris flows. Storms across the west develop quickly, leaving little room for lead time in flashy terrain.

GJT WATCHES/WARNINGS/ADVISORIES

CO...None. UT...None.