textproduct: Grand Junction

KEY MESSAGES

- Widespread rain is expected Wednesday through Friday.

- Strong to severe storms cannot be ruled out near the Four Corners on Wednesday and Thursday.

- The potential for flooding increases Thursday and Friday, especially for portions of southeast Utah and southwest Colorado.

- Rainfall amounts in the southern mountains range from 1-3 inches with higher amounts of 2-4" or more possible in the San Juans and southern foothills.

DISCUSSION

Issued at 136 PM MDT Tue Oct 20 2026

HAZARDOUS WEATHER POSSIBLE THROUGH FRIDAY:

Remnant moisture from a tropical cyclone formerly known as Trudy will move into the Four Corners tomorrow before tracking northeastward across eastern Utah and western Colorado through Friday morning. A plethora of weather hazards are possible with this system including flooding, flash flooding, strong to severe thunderstorms, and snow above 12,000-13,000 feet. As a result, a Flood watch has been issued for parts of southeast Utah and southwest Colorado from 12 PM Wednesday through 12 PM Friday.

Wednesday:

Showers and storms develop along the moisture transport gradient as early as tomorrow morning, with storms strengthening throughout the afternoon. This initial push of convection tomorrow will pose a localized threat for heavy rainfall and flash flooding if stronger storms develop, especially if storms begin to train over the same areas. Isolated severe storms are possible in the Four Corners region capable of producing large hail, damaging wind, and brief tornadoes as well due to the presence of modest instability and strong shear. However, the highest potential for severe weather will remain off to our southwest in northwest into central Arizona. Stay weather aware if you have outdoor activities planned! If you experience any of the hazards noted above, please report them to NWS Grand Junction.

Wednesday night - Thursday night:

With an anomalously moist tropical airmass overhead, widespread rainfall takes hold of the forecast area Wednesday night. Please see the Hydrology Section below for more information concerning the threat for flooding from this period of moderate to widespread rainfall.

Another round of strong to severe storms cannot be ruled out on Thursday afternoon/evening with marginal instability and strong wind shear present. However, widespread cloud cover adds a layer of uncertainty to the forecast and may inhibit surface heating. If stronger storms develop, isolated damaging wind, large hail, brief tornadoes are possible. We have low confidence in this aspect of the forecast.

Friday:

Models have continued to key in on a dry slot quickly evacuating the tropical moisture from the region on Friday morning. Even after it stops raining, the risk for flooding and flash flooding will remain elevated on Friday morning as water continues to work through the system. Do not let your guard down right away! We'll have a better idea of how long flooding may continue to cause issues after we get a better sense of how much rainfall is received on Thursday.

LOOKING AHEAD:

Chances for light precipitation (valley rain, mountain snow above 10,000 feet) continue through the weekend as a low pressure system, currently spinning off the California coast, traverses the Intermountain West. Plenty of uncertainty remains in how this low will evolve as it moves inland, but ensemble guidance tends to show a weakening system by the time it reaches our forecast area. Regardless, this system will provide enough forcing for scattered to widespread precipitation as it moves through, alongside a brief reduction in temperatures.

AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/

Issued at 1118 AM MDT Tue Oct 20 2026

VFR conditions will persist through much of this period. Some low cloud debris is still hanging around the terrain, but should be on the wane this afternoon. Kept ceilings in KEGE for a bit longer to allow time to disperse. Tropical moisture intrusion returns late tonight from the Southwest. This will bring some ceilings and showers late in the period from the Four Corners northeast to about the highway 50 corridor, then spread beyond in latter TAF periods. Breakpoint ceilings will likely impact terminals Wednesday morning and continue beyond as the tropical moisture deepens in the atmosphere.

HYDROLOGY

Issued at 102 PM MDT Tue Oct 20 2026

Hydrologic concerns ramp up tomorrow (Wednesday), due to the potential for thunderstorm development. Atmospheric moisture increases under strong south-southwesterly flow, lofting an abundance of warm tropical moisture across the forecast area. While bands of showers expand as early as Wednesday morning, thunderstorms are expected to move into east/southeast Utah tomorrow afternoon. Southeast Utah and lower valleys along the CO/NM border show the highest pockets of instability, which focuses the better confidence for flash flooding across desert floors and dry washes. Coverage of rainfall rates exceeding 0.5 inches in an hour remains low even 24 hours out. However, whatever embedded thunderstorms that develop tomorrow will only help saturate soils leading into the main surge of moisture expected Wednesday night through Thursday.

The bulk of precipitation remains on track for Thursday, with generally 1 to 3 inches of rain falling across the southern half the CWA within a 24 to 36 hour window. Bullseye QPFs are highest over the San Juan's, where locally higher amounts of 4 to 5 inches are possible. This system continues to track anomalously warm, as the main moisture plume remains well ahead of a cold, closed low deepening along the Pacific Coast. Thus, rain on snow is a viable concern. Snow levels are forecast above 12-13 kft throughout the day Thursday, which will likely result in melting much of the existing early-season snow pack. The combined runoff from rain and rain-on-snow will result in a rapid rise in many of our creeks, streams and rivers. Modeled responses also nudged upward across many river forecast points across southwest Colorado. We have the highest confidence in minor flooding and impacts along the San Juan River, Piedra, Animas, La Plata Rivers and above Vallecito Reservoir. However, other creeks and tributaries within the Four Corners region remain susceptible. All river responses are heavily dependent on where the heaviest precipitation falls, so please continue to monitor the forecast as the week unfolds.

GJT WATCHES/WARNINGS/ADVISORIES

CO...Flood Watch from Wednesday afternoon through Friday morning for COZ019-021>023. UT...Flood Watch from Wednesday afternoon through Friday morning for UTZ022-027>029.