textproduct: Grand Junction

KEY MESSAGES

- Warmer and drier conditions over the weekend.

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

DISCUSSION

Issued at 1245 PM MDT Sat Sep 26 2026

PREDOMINATELY DRY THIS WEEKEND:

A flattened high pressure across eastern Utah and Western Colorado is bringing mostly sunny skies to the region with subsidence under the ridge and the drier zonal flow aloft. Look for mild Fall temperatures today near normal to five degrees above normal. There are some low to mid level clouds developing across the region from residual moisture hanging around and no wind to sweep it out. We may see a few isolated orographic showers and thunderstorms this afternoon with the moisture in place, but not seeing any severe weather likely. We'll see things start to change Sunday as the trough descends through the Pacific Northwest , shifting the flow more southwesterly pulling the tropical moisture into the region from hurricanes Odalys and Polo. We'll see increasing clouds moving into the region with the monsoonal surge, but otherwise, it will be similar to today.

WET WEEK AHEAD:

The latest runs of the GFS and GEFS are tracking the low farther north across southwestern Utah/southern Nevada Monday night which would spell stronger thunderstorms for southeastern Utah and southwestern Colorado Monday into Tuesday with the cold air advection aloft and the increased dynamics. Pwats are not extreme at around an inch, but with the increased instability and dynamics, could produce heavy rain and flash flooding with the stronger storms. The Weather Prediction Center has drawn the southern areas under a moderate risk for excessive rainfall for day three and marginal to slight for day four. There is still a lot of uncertainty with continued inconsistent run-to-run solutions among the models. Holding off on issuing headlines 'til we see tonight's or even tomorrow's model runs to get another/better look at the system. Otherwise, we can look for a cooler, wet period through Wednesday with showers and thunderstorms, and temperatures five to ten degrees below normal. Beyond Wednesday, conditions dry out with temperatures returning to near normal for the start of October.

AVIATION /18Z TAFS THROUGH 18Z SUNDAY/

Issued at 1245 PM MDT Sat Sep 26 2026

VFR conditions remain in place over the next 24 hours. Some showers and midlevel clouds will form over the higher terrain this afternoon while high clouds move in during the evening hours. A few gusts of 15 to 20 mph will occur this afternoon as well.

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. Please continue to monitor the forecast as these systems evolve. Especially for those who reside and/or plan to recreate in the southwest quadrant of the forecast area.

GJT WATCHES/WARNINGS/ADVISORIES

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