textproduct: Grand Junction

KEY MESSAGES

- Warmer and drier conditions continue Sunday.

- Another push of moisture will arrive by Monday, bringing widespread moderate to heavy precipitation through midweek.

- Flood Watch in effect from 6am Monday through 6am Wednesday for southern portions of the forecast area.

- Drier conditions return late week.

DISCUSSION

Issued at 1029 PM MDT Sat Sep 26 2026

A pattern shift begins to develop on Sunday as an open trough digging out of the PACNW begins to scoop tropical moisture into the southwesterly flow over the Southwest. Temperatures will remain near normal Sunday afternoon, but skies will cloud over as upper level moisture fills in. A few isolated showers could develop on the mountains Sunday afternoon, but measurable rain will remain in short supply as we wait on the deeper tropical moisture to develop Sunday night. PWAT values surge in excess of 200 percent of normal Sunday night for the Four Corners and much of southwest CO. With the jet overhead providing some lift, we should see rain develop across much of the region by daybreak Monday. This will begin a wet 48 hours for our CWA as the remnant moisture from multiple tropical storms gets entrained into the southwesterly jet streak aloft.

With this jet overhead Monday, forcing and moisture will work in concert to produce training showers over much of southeast UT and southwest CO. The best rainfall rates appear to remain confined to areas south and east of the Colorado Basin for eastern UT and south of the Uncompahgre Plateau/San Juans. Areas to the north will get some wetting rain, but flash flood concerns trend better to the south. The upper low begins to lift out of the region on Tuesday, taking much of the moisture with it. However, convection around the low will likely continue the threat for flash flooding on rain soaked soils.

High pressure returns to the region Wednesday and begins to dry things out in the atmosphere, with temperatures returning back towards normal values Thursday and Friday. Models begin to hint at a clipper system dragging through northern CO next weekend. This could produce some cooler conditions for the northern mountains, depending on the evolution of this disturbance.

AVIATION /18Z TAFS THROUGH 18Z MONDAY/

Issued at 1146 AM MDT Sun Sep 27 2026

Clouds are streaming in from the southwest as moisture increases. An occasional gust of 15 to 20 kts is also possible this afternoon but won't be widespread. Clouds will begin lowering during the evening and overnight with showers developing over southern Colorado. VFR conditions will remain in place through the day. Showers will become more widespread tomorrow morning with MVFR conditions becoming more likely.

HYDROLOGY

Issued at 233 PM MDT Fri Sep 25 2026

In the wake of today's precipitation, our attention will turn to the Eastern Pacific. Tropical moisture is anticipated to spread across the Desert Southwest early next week, drawing moisture from a pair of Hurricanes; Odalys and Polo. The forecast becomes increasingly complex due to a closed low currently forecast to drive across the Southwest CONUS as Hurricane Polo approaches the Baja California Peninsula. Strong southerly winds ahead of the low are expected to pull tropical moisture towards eastern Utah and western Colorado as early as Monday morning. The challenge and uncertainty in our precipitation forecast increase as the week progresses and the low traverses our southern States. Excessive rainfall is most probable over AZ and NM, attm, but the northerly extent poses a threat to our southern San Juan river basins. Current forecasts suggests 1 to 3 inches of rain over Monday morning through Wednesday. At face value, rivers and tributaries will see a bump up due to said moisture. However, localized heavier amounts could result in minor flooding across the southern San Juan foothills and communities further downstream.

Rivers have responded rapidly to recent rainfall due to saturated soils and increased runoff potential. Thus, prolonged periods of additional rainfall over these regions would trigger a similar response. The current precipitation forecast suggests larger peaks in several creeks and rivers than what has been observed over the previous 7 days. However, high end probabilistic rainfall amounts (i.e. above 90th percentile) may lead to rivers exceeding action stage to minor flooding. Most probable basins to see significant rises include; the Rio Blanco, San Juan, Piedra, Los Pinos/Vallecito Creek, and the Animas River Basins.

Convective storms and periods of heavy rainfall fed from said tropical moisture could result in localized flooding impacts across the CWA, however, confidence decreases rapidly north of the San Juans. Confidence has increased enough for a Flood Watch to be issued for southern portions of the forecast area valid from 6am Monday through 6am Wednesday. Even so, please continue to monitor the latest forecasts especially for those who reside and/or plan to recreate in the Watch areas.

GJT WATCHES/WARNINGS/ADVISORIES

CO...Flood Watch from Monday morning through late Tuesday night for COZ017>023. UT...Flood Watch from Monday morning through late Tuesday night for UTZ022-028-029.