textproduct: Grand Junction

KEY MESSAGES

- Increased moisture will arrive Monday, bringing widespread precipitation chances through midweek.

- This rainfall increases flooding concerns across vulnerable terrain and burn scars, as well as areas that received substantial rain from the last system.

- A Flood Watch is in effect for southeast Utah and southwest Colorado from 6AM Monday through 6AM Wednesday.

DISCUSSION

Issued at 942 PM MDT Sun Sep 27 2026

WIDESPREAD PRECIPITATION MONDAY + TUESDAY:

Moisture advection from the tropical storm activity in the Eastern Pacific will bring anomalous moisture to our region through at least midweek. PWAT anomalies will be upwards of 250% of normal for a good chunk of the CWA, especially south of I-70. This means a return to widespread precipitation chances for much of the region. Shower activity is expected to start in the Four Corners area in the early morning hours on Monday, spreading northward by sunrise. Additionally, this moisture will be accompanied by synoptic forcing, as a closed upper level low digs southward through California on Monday, and then across the Desert Southwest on Tuesday and Wednesday. A jet streak aloft and energy from a trough axis will work in tandem to create lift for showers and storms. This means there may be enough forcing from those factors to create embedded thunderstorms, but even recent HiRes guidance continues to favor the stratiform rainfall storm mode. The potential for widespread precipitation sticks around for Tuesday as well before the trough axis begins tracking eastwards across the Divide by Wednesday.

The potential for prolonged periods of rainfall, including in areas that have recently received substantial rainfall poses flooding concerns for the coming days. Hence, a Flood Watch is in effect for southeast Utah and southwest Colorado from 6AM Monday through 6AM Wednesday. Please see the hydrology section below for more information on those flooding concerns. Additionally, if you plan on recreating outdoors over the next few days, continue to keep on eye on the forecast and make yourself aware of any active watches or warnings in your area.

Rainfall amounts carry some uncertainty because models disagree on the exact track of the closed low and key areas of forcing. Still, south- and southwest-facing slopes in the San Juans are favored. Most of the Four Corners area has an 80-90% chance of exceeding 1" of rain by 6AM Wednesday, while locations like Durango, Pagosa Springs, and Ignacio have a 60-70% chance of exceeding 2.5" for the same time period.

Lastly, increased cloud cover will knock temperatures down quite a bit from Sunday's highs. Most spots will stay cooler than average for the first half of the work week.

MOISTURE BEGINS TO EXIT THE REGION WEDNESDAY:

By Wednesday, the elevated moisture and closed low will move east of the Rocky Mountains, bringing back drier weather for the area. However, lingering moisture may be enough to support additional convection over the higher terrain Wednesday afternoon.

AVIATION /18Z TAFS THROUGH 18Z TUESDAY/

Issued at 1149 AM MDT Mon Sep 28 2026

Showers continue to fill in across the CWA and will be ongoing through the afternoon/evening hours. Broken to mostly overcast skies are being reported at many TAF sites, with a continuation of those conditions into the overnight hours. Winds will be generally light and terrain driven under these showers. Where heavier rainfall is present, expect flight conditions to vary between low end VFR and MVFR, due to low cigs and visibility constraints. ILS breakpoints will likely be met for some terminals and mountain obstructions will be common.

HYDROLOGY

Issued at 942 PM MDT Sun Sep 27 2026

Strong southwesterly winds ahead of a closed low centered over California will pull tropical moisture from Tropical Storm Odalys and Hurricane Polo towards eastern Utah and western Colorado, with atmospheric moisture peaking in our area on Monday. The northerly extent of the expected excessive rainfall poses a threat to our southern San Juan river basins. Current forecasts suggest 1 to 4 inches of rain Monday morning through early Wednesday. At face value, rivers and tributaries will see a rise due to the forecast rainfall. However, localized heavier amounts could result in 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 recently observed. 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. 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 through late Tuesday night for COZ017>023. UT...Flood Watch through late Tuesday night for UTZ022-028-029.