textproduct: Grand Junction

KEY MESSAGES

- Isolated showers and seasonable temperatures continue Tuesday.

- Widespread rain returns Wednesday through Friday.

- 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 locally higher amounts possible in the San Juans.

DISCUSSION

Issued at 1102 PM MDT Mon Oct 19 2026

High pressure over the Gulf drifting west into Mexico and a deep low currently off the Oregon Coast descending south off the West Coast will dominate the weather pattern through the rest of the week and possibly into early next week. The current southwesterly flow is pulling Pacific moisture up through Southern California and the Desert Southwest into the region that supported weak isolated light showers with a few thunderstorms today, and will again tomorrow, but coverage does look to be a little more isolated. As the low bottoms out off the Southern California Coast by Wednesday morning, turning to the northeast to track up across the Great Basin and Utah by Friday, the High pressure moves in over northeastern Mexico to set up a more southerly flow than we saw with the last tropical surge of moisture. This scenario sets the deeper plume of tropical moisture from the remnants of Hurricane Trudy to plow into the southern mountains where current guidance has the bulk of the rain falling, and casting a rain shadow to the north in the central and northern mountains. This being said, there is still a lot of uncertainty creeping into the forecast as early as Wednesday. The latest guidance is sliding the moist plume to the west a bit that would allow more moisture to push north into southern Utah and to the east into the central and northern Colorado areas. The Atmospheric River (AR) models do support this solution with Integrated Vapor Transport (IVT) values up to 500 kg/m/s pushing into the central and northern areas. As a result, storm totals have increased to one to two inches rain in the central mountains and up to an inch farther north. Mean while the southern face of the San Juan and Abajo Mountains will see two to three inches rain with locally higher amounts possible. This system is a very warm system with snow levels remaining above 12K ft through Thursday creating a risk for receiving rain on snow through the southern mountains that can lead to high stream flows across the southern areas of Colorado and Utah. In fact, the River Forecast Center is forecasting some of the rivers in this area to reach flood stage with this system. Understand that the forecast remains fluid at this time, and key details will shift over the coming days. Stay tuned for updates on this. Look for the heaviest rains to fall Wednesday night into Thursday as cooler air and stronger jet dynamics move in aloft supporting stronger thunderstorms with periods of heavy rain. These stronger storms may lead to localized flash flooding possible across much of eastern Utah and Western Colorado. Stay tuned on this too as the forecast develops.

The showers and thunderstorms will taper off Friday as drier air moves in from the southwest. As the low passes to the northwest, it will drag a cold front across the northern areas Friday mostly along and north of I-70, dropping temperatures from Thursday's highs about ten degrees. Residual moisture across the region will spawn showers mostly over the higher terrain Saturday afternoon and again Sunday before things are finished.

AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/

Issued at 1146 PM MDT Mon Oct 19 2026

FEW to BKN mid and low level clouds are moving across the area, along with some terrain-based showers. Potential TAF site impacts, which include drops below ILS breakpoints and brief periods of MVFR conditions, are possible through 12Z at KTEX, KDRO, and KEGE. Isolated afternoon showers and thunderstorms are possible after 18Z. Winds will be light and terrain driven overnight.

HYDROLOGY

Issued at 300 PM MDT Mon Oct 19 2026

Strong southwesterly winds develop overhead on Wednesday, which will open the atmospheric flood gates and draw in moisture tied to Tropical Storm Trudy. Yet another decaying tropical system will fuel widespread showers across the Desert Southwest and southern Colorado Rockies through the end of the week. Rainfall totals are subject to change, however, current guidance shows 1 to 3 inches of rain across the Four Corners region, with locally higher amounts expected. The warm tropical moisture is also throwing a wrecking ball at normal snow levels for this time of year, with rain possible above 12,000' through Thursday. SNOTEL sites across the San Juans indicate 1 to 2 inches of SWE accumulated from last week's storms. If the the warm tropical moisture arrives as rain up high, we can anticipate accelerated runoff due to rain on snow for our upper level basins.

In addition, convective storms are not out of the question, preceding and following the main atmospheric plume of moisture. Heavy rainfall rates ahead of the system (i.e. Wednesday afternoon) may locally enhance water levels in rivers and washes, or at least, prime soils for more efficient runoff come Thursday. Confidence in the details of heavy precipitation rates and coverage are low at this time, but certainly noteworthy for the event's entirety.

The complexity Trudy brings, in terms of precipitation rates, totals and temperatures, raises our concern for another round of flooding and flash flooding of rivers, streams, creeks and normally dry arroyos. The latest river forecasts provided by CBRFC suggest minor flooding for the San Juan River, near Pagosa Springs, CO. In addition, rivers reaching bankfull to near minor flood stage is possible for the Piedra and Animas basins, with a 1 to 2 foot rise expected in nearby basins. Although timing is likely to change, expect a rapid rise in rivers, creeks, and dry washes Thursday into Friday.

GJT WATCHES/WARNINGS/ADVISORIES

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