textproduct: Grand Junction

KEY MESSAGES

- Widespread rain is expected tomorrow through early Friday.

- Strong to severe storms will be possible near the Four Corners...favoring southeast Utah...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 159 PM MDT Wed Oct 21 2026

HAZARDOUS WEATHER POSSIBLE THROUGH FRIDAY:

Remnant moisture from a tropical cyclone formerly known as Trudy is moving northeastward across eastern Utah and western Colorado. 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 is in effect for parts of southeast Utah and southwest Colorado through 12 PM Friday.

This afternoon:

An initial push of convection has developed over the Four Corners region and 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 capable of producing large hail, damaging wind, and brief tornadoes cannot be ruled out due to the presence of modest instability and strong shear. However, the highest potential for severe weather will remain off to our southwest strong downstream blocking ridge will favor the trough over the West to linger upstream of us through early Tuesday. This will keep us in strong Southwest flow aloft and a generally warmer and moist environment. As mentioned earlier the highly anomalous tropical plume will be advecting north of the area tonight but still remain above normal until the trough passes and we begin to dry out after midweek. Winds will remain breezy in the leading edge of the trough with gusts of 25 to 35 mph...with a few higher gusts possible in the 4 Corners region tomorrow afternoon. Higher gust over the terrain can be expected as well. The parent low in this trough is over the Oregon this evening and model consensus has it digging through the Intermountain West to the 4 Corners region by Tuesday evening. This will keep broad ascent over our area supported by the jet aloft which will keep working on the moisture to produce showers through Tuesday morning. The best chances will be over the western 2/3 of the CWA and the San Juans with less coverage over the central divide. Ascent increases significantly through the day Tuesday as the upper low digs through the lower Great Basin. This will ooze a cold front through the area under the strong QG signal 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.

Tonight - 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 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 /00Z TAFS THROUGH 00Z FRIDAY/

Issued at 546 PM MDT Wed Oct 21 2026

Expect widespread light rain and moderate rain showers across he region through the TAF period. Currently scattered embedded thunderstorms are limited to the southern areas of southeastern Utah and southwestern Colorado, but will spread north to along and west of the line from KVEL to KCPW after 12Z. Winds will be generally light across the region through the TAF period, but expect outflow gusts to 40 kts associated with thunderstorms overnight increasing to over 50 kts after 12Z. Conditions will be mostly MVFR to IFR with the showers and thunderstorms, below ILS breakpoints for most mountain TAF sites for the next 24 hours.

HYDROLOGY

Issued at 257 PM MDT Wed Oct 21 2026

Hydrologic concerns remain elevated through Friday due to the influx of highly anomalous tropical moisture across the 4 Corners area into the Central Rockies. Potential hazards include localized flash flooding from thunderstorms producing heavy rainfall rates and river flooding due to a prolonged period of widespread moderate to heavy rainfall.

Southeast Utah and the lower valleys along the CO/NM border will be under the highest threat of strong to severe thunderstorms capable of producing flash flooding across desert floors and dry washes the through tomorrow evening.

There is a moderate risk of excessive rainfall leading to flooding across portions of the San Juans and adjacent southerly valleys where precipitation totals of 2 to 4 inches will be possible. The bulk of this precipitation will fall overnight through early Friday morning. Higher precipitation totals over portions of the southern San Juans of 4 to 5 inches are definitely possible. An additional concern of rain on snow leading to additional runoff making it into the waterways. Snow levels are forecast above 12-13 kft throughout the day Thursday, which will likely result in melting of some 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 suggest several rivers reaching bankfull or higher at river forecast points across southwest Colorado and southeast Utah. The highest confidence in minor flooding and related 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 through Friday morning for COZ019-021>023. UT...Flood Watch through Friday morning for UTZ022-027>029.