textproduct: Grand Junction

KEY MESSAGES

- Precipitation chances increase through Monday. Stronger storms may be capable of producing flash flooding.

- Daily showers generally over the high terrain expected Tuesday through the end of the week.

DISCUSSION

Issued at 1006 PM MDT Sat Sep 5 2026

Southwesterly flow ahead of a deep trough along the west coast is set up overhead. Amidst this flow, a pool of substantial moisture is nudging into southern Utah per water vapor imagery. According to ensembles, we should expect this pool to continue seeping into the Intermountain West over the coming 48 hours, bringing impacts to our CWA. Per the 00Z GJT sounding, low- levels are still very dry, and model guidance suggests that even as we see the plume of moisture begin drifting from the west Sunday, it will take some time for near- surface conditions to saturate enough to support significant rainfall. With this, look for Sunday's storm coverage to be generally isolated for most of the region aside from northeastern Utah where the stream of moisture will be the strongest.

Overnight Sunday into Monday morning, the moisture plume centers itself over the CWA. With stabilization from nighttime cooling and without any significant upper-level dynamics or forcing mechanisms, look for precipitation to be steady and relatively light throughout the night. Where things get more interesting is after sunrise on Monday. Though the bulk of the moisture will have come and gone, wetter low-levels will remain, supporting more storm development. The caveat to these storms is the denser cloud cover that is anticipated to be in place during the morning hours, dampening destabilization. What this means for us is that storm mode is trending in a more stratiform direction instead of discrete cells capable of heavier localized rainfall. Some early CAM guidance suggests that a few pockets of 300+ J/kg of CAPE may manifest in spite of the morning cloud cover, but this likely would result in little more than a few stronger cells embedded within stratiform rainfall. Though this supports a broader areal coverage of wetting rains without amplifying the hydrologic threat, we have seen in recent days that even stratiform rains are capable of producing flash flooding, partially due to the more saturated nature of soils region-wide. So don't go discounting the flash flood threat come Monday even should stratiform storms dominate. This is especially true for vulnerable areas and recent burn scars.

Beyond Monday, the trough to our west breaks down and transits eastwards, producing more zonal flow across much of the CONUS. This elongates the Southern Plains high, pushing the high westwards towards us and re-establishing in the southwestern CONUS. Exactly how far west the high will get shoved is a point of uncertainty, one which potentially holds significant ramifications on mid-to-late-week storm potential. Moisture from the Pacific is expected to get drawn around the high into the southwestern US. Regardless of the high's position, we are unlikely to be in a favorable position to receive the brunt of this moisture, but the exact trajectory of the pool will still have notable impacts on the resulting precipitation over the West Slope. At the very least, daily showers along the high terrain are expected throughout the week. As it stands, uncertainty is too high to speculate on the details, so stay tuned over the coming days for additional information.

AVIATION /06Z TAFS THROUGH 06Z MONDAY/

Issued at 1118 PM MDT Sat Sep 5 2026

VFR conditions will prevail over the next 24 hours with mid to high level clouds passing through at times. The most probable threat of a thunderstorm or shower will be over KVEL tomorrow afternoon and evening. Better moisture arrives late with precipitation coverage increasing for Monday.

GJT WATCHES/WARNINGS/ADVISORIES

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