textproduct: Grand Junction

KEY MESSAGES

- Isolated to scattered storms will develop Friday. A few storms may be capable of strong outflow gusts, small hail, and localized heavy rainfall.

- Coverage of showers and storms decreases on Saturday with most locations dry on Sunday and Monday.

- Another bout of moisture arrives mid next week. This could bring more showers and thunderstorms to the region.

DISCUSSION

Issued at 956 PM MDT Thu Sep 17 2026

MOISTURE DIMINISHES THROUGH THE WEEKEND, BUT STORMS CONTINUE:

The western CONUS low begins a steady trek through the Great Basin and, eventually, the Intermountain West. This begins to push the pool of powerful moisture out of the region and begins a slow drying out across the West Slope. On Friday though, we will still be holding onto quite a bit of moisture with PWAT's somewhere around 200% of normal give or take. We will reside underneath the entrance of a weak jet streak as well, so there is some evidence that Friday will actually produce some relatively strong storms. Cloud cover is still expected to be dense in the morning, so that will limit storm coverage and updraft strength, but we've already seen a couple days this week exceed expectations, so don't rule out a few instances of powerful outflows, sub-severe hail, and localized heavy rainfall capable of exacerbating flash flooding concerns. According to CAM's, these types of storms are most likely in the far northwest and southeast corners of the CWA during the afternoon and evening, but other regions across the CWA could still see isolated impacts.

By Saturday, PWAT's should be firmly below 200% of normal. This is enough moisture to keep some isolated storms going, but certainly we will see coverage continue to diminish. By Sunday, moisture will be near-normal, or maybe even a touch below normal. This comes as the trough's axis crosses over the CWA. Still, flow around the base of the trough looks to be powerful, and as such, some orographic showers could develop. Impacts would likely be minimal with these storms though.

MOISTURE QUICKLY RETURNS:

The relatively dry period won't stick around for too long as another low follows behind the first, moving into the southwestern CONUS on Monday. There's plenty of uncertainty among ensembles on how much moisture will be drawn up through the southwesterly flow. The GFS Ens keeps the plume mostly to the southeast while the ECMWF Ens draws the plume more directly overhead. In either case, this round of moisture is expected to bring about another round of showers and thunderstorms. It'd take some time for the moisture to arrive, so Monday will likely still be on the quiet side with the arrival of stormy skies occurring Tuesday or Wednesday. By this point though, models are diverging by quite a bit as evident through cluster analysis. Some evidence suggest the low will persist and swing through our region, which would support more powerful storm development, while other guidance appears to more quickly break down the trough before it can make its way further inland. Once we gain more clarity on these details we'll be able to speculate on potential impacts.

AVIATION /06Z TAFS THROUGH 06Z SATURDAY/

Issued at 1139 PM MDT Thu Sep 17 2026

Quieter start to the late evening forecast with most areas rain-free and at VFR conditions. There are some ILS cigs in the eastern TAF sites which may linger past sunrise. Also showers and isolated thunderstorms may progress toward and across KVEL through the early morning hours. Support for an increase in shower and thunderstorm coverage come again by sunrise and expect most TAF sites will be under threat of a passing shower/storm through the remainder of the forecast. There is a small probability of MVFR if the right storm moves through. Also confidence is low but will be watching for stratus and/or fog development at some of the favored sites in this moist regime.

GJT WATCHES/WARNINGS/ADVISORIES

CO...Flood Watch until midnight MDT tonight for COZ018-019-021>023. UT...Flood Watch until midnight MDT tonight for UTZ022-028-029.