textproduct: Grand Junction

KEY MESSAGES

- Isolated showers and thunderstorms expected over the high terrain today and Friday. Main concerns will be gusty outflow winds and lightning.

- Triple-digit temperatures expected today and Friday in lower valleys.

- Precipitation potential increases this weekend with more widespread coverage of showers and thunderstorms. Flash flooding will be possible, especially Saturday.

DISCUSSION

Issued at 1216 PM MDT Thu Aug 20 2026

Some morning convection occurred as a weak shortwave moved through the area, exiting by mid morning. High pressure remains in place across the area with residual moisture trapped underneath the high allowing for isolated to scattered afternoon convection over the high terrain. A vort max does look to track across the north this evening into the overnight which could result in some lingering activity, but overall should be a hot and dry day otherwise. Friday begins a transition day with a low pressure trough approaching the Pacific Northwest coast. However, high pressure still remains anchored over the Four Corners region, providing another day of scattered showers and thunderstorms mainly over the high terrain. The main concerns with any storm activity remain gusty outflow winds to 35 mph and lightning with some localized wetting rain in the stronger convection. While hydro concerns will be minimal through Friday due to the drier low levels, stronger convection could still result in an isolated flash flood risk over burn scar areas. The main point of interest as we close out the work week will be the abnormally warm temperatures underneath this high pressure, with triple digits possible in many valley locations Thursday and Friday, particularly the lower desert valleys of eastern Utah and west-central Colorado. Because of the lingering moisture in the Intermountain West, cloud cover will play a role in just how hot these temperatures will be allowed to get, but regardless, look for highs to remain about 10 degrees above normal until we hit the weekend.

WET WEATHER RETURNS THIS WEEKEND:

Saturday begins the ramp up in wet weather returning to the region as the low pressure trough pushes inland across the Pacific Northwest and nudges the high pressure ridge eastward, putting us in a more favorable trajectory for monsoonal moisture to surge back northward in southerly flow. While the strongest portion of this moisture plume will push across the Great Basin to our west with PWAT anomalies increasing towards 200 percent of normal, PWAT will increase towards an inch or greater across our CWA on Saturday, which is still a good jump from where it stands currently. Dew points also rise well into the 50s for much of the area. Hydro impacts become more probable during this period as a robust shortwave moves through the southerly flow late Saturday afternoon into the evening across eastern Utah and moves through northwest Colorado over the top of the ridge by Saturday evening and overnight. This added forcing combined with the increase in moisture could result in more widespread storm activity late in the day on Saturday and potentially continuing overnight, including a better chance of wetting rain in the lower elevations as well. The aforementioned Pacific Northwest trough looks to move across the northern Rockies Sunday, so with moisture already in place, this will result in more scattered thunderstorm development as the flow becomes more westerly. Due to the projected placement of this shot of moisture, there`s still wiggle room for models to nudge it further into our CWA, so don`t count out a more widespread event. As guidance stands now though, the flash flood risk appears more moderate with highest potential over the burn scar areas. Hi-res models will reveal much more insight into this system, so stay tuned as we begin to receive this model guidance over the coming days.

It does appear like drier air tries to work back in for early to mid next week as the high pressure shifts back a bit westward and builds overhead. However, lingering moisture will still result in daily afternoon thunderstorms favoring the high terrain but the coverage does not appear as widespread as this weekend with the deeper moisture and more robust forcing in place. Temperatures are expected to cool a bit closer to normal this weekend into early next week with the increase in clouds and precipitation.

AVIATION /18Z TAFS THROUGH 18Z FRIDAY/

Issued at 1118 AM MDT Thu Aug 20 2026

VFR conditions are expected to prevail through the TAF period. Shower and storm chances remain confined to KDRO and KGUC this afternoon, with most other terminals remaining out of the threat. However, gusty outflows have the ability to reach nearby terminals. Winds will mostly follow typical terrain driven patterns during the period, with periodic gustiness possible this afternoon and into the evening hours for some TAF sites. Mid and high level clouds are forecast to develop south of I-70 initially and will begin spreading northward by the late afternoon hours.

GJT WATCHES/WARNINGS/ADVISORIES

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