textproduct: Grand Junction

KEY MESSAGES

- Isolated showers and seasonable temperatures to start the work week.

- Widespread rain returns Wednesday through Friday.

- The potential for flooding increases on 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 1112 AM MDT Mon Oct 19 2026

ISOLATED SHOWERS AND SEASONABLE TEMPS TO BEGIN THE WORK WEEK:

Broad southwesterly flow will dominate the start of the work week, maintaining moisture advection across the region. Expect a continuation of cloud cover along with isolated showers through Tuesday. Modest warm air advection will nudge high temperatures closer to seasonal normals despite the increased cloud cover. While localized breezy conditions could accompany collapsing showers, organized convection is not anticipated.

WIDESPREAD RAIN AND FLOOD POTENTIAL LATE-WEEK:

By Wednesday, a strong low pressure system drops southward along the California coast, while an upper level jet noses into the Four Corners region. These two features will work in tandem to bring remnant moisture from what is now Hurricane Trudy into the region, bringing the return of widespread precipitation chances. Initial model solutions depict the most likely time period for widespread showers to be Wednesday night through Thursday night. It is also important to note that a large majority of the precipitation from this system will fall as rain, with the pool of colder temperatures staying well north of the forecast area. As a result, snow levels will remain high, generally at or above 12,000 feet. Given the prospect of high-elevation rain falling onto antecedent snowpack and saturated soils from last week's precipitation, flash flooding and hydrologic impacts will be monitored closely as the system progresses. The highest amounts of rainfall are currently showing up in the southern mountains where 1-3 inches of rainfall are possible. The San Juans look to take the brunt from this system so locally higher amounts are possible. In fact, some of the river forecasts in that area are reaching flood stage. Ensemble guidance supports PWATs upwards of 250-300% of normal, providing another strong signal to monitor for potential impacts. Keep in mind that the forecast remains fluid this far out, and key details may shift over the coming days. Stay tuned for updates.

Precipitation chances continue into Friday afternoon, though coverage will gradually taper off. Meanwhile, the low pressure system will be absorbed into the main flow, driving a frontal passage through the area. This will bring cooler temperatures on Friday, dropping highs by 5 to 10 degrees compared to Thursday and potentially taking overnight temperatures back below freezing.

AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/

Issued at 521 PM MDT Mon Oct 19 2026

Midlevel clouds along with scattered showers and a few thunderstorms have filled in across eastern Utah and western Colorado. Terminals currently remain above breakpoints, but could drop below ILS/into MVFR conditions for short periods with passing showers. Have included tempo groups for most terminals through 03z to account for this. Midlevel ceilings will stick around through roughly 12z tomorrow, before lifting. Winds will be light and follow typical terrain driven patterns.

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.