textproduct: Grand Junction

KEY MESSAGES

- A pattern change arrives through the weekend bringing another round of tropical moisture to the region.

- Rainfall totals of 1-2 inches and locally higher are possible over the eastern Utah mountains and the San Juans. Moderate to heavy rainfall rates are possible and smaller drainages and arroyos will be susceptible to excess runoff. Burn scars will will also be under threat of debris flows.

- Strong thunderstorms are possible the Saturday and Sunday afternoon with gusty outflow winds the main threat. A few more organized storms could contain larger hail and bring a flash flood threat.

- Expect strong winds 30 to 40 mph with gusts 40 to 50 mph Sunday with higher gusts over the terrain. - Another pattern change is possible by the middle of next week with an early season winter storm. Snow accumulation is possible above 10,000 ft with snow possible down to 8,000 ft. Forecast confidence is low at this time.

DISCUSSION

Issued at 1046 PM MDT Fri Oct 9 2026

The 10/00Z H500 hand analysis and satellite imagery was showing the Atlantic tropical system moving across the Florida Panhandle and the Pacific storm well off the central Baja coastline. Otherwise a fairly progressive pattern is in place across the lower 48 but this will change significantly over the next 24 to 36 hours. This is due the main driver of the change which is a very strong trough currently across the northern border in BC. This trough will dig into the PacNW tomorrow and carve well off the SoCal coast by early Sunday. This effectively puts strong Southwest flow from the Baja Region across the 4 Corners into the Northern High Plains. It should be no surprise then that copious amounts of tropical moisture will be transported across the Intermountain West beginning as early as tonight...but more robust by tomorrow night. PWAT continues to surge to near an inch by midnight Sunday morning which will be near a climatological maxima and at least in the 90th percentile or higher. It will drop back some start next week but not really dry out until we head into the late week/weekend period. So a wet and cool forecast is on tap for much of this forecast with tomorrow and Sunday a transition period with temperatures warmer or closer to normal. Grabbing onto the finer details remains a challenge over the next several days. How will cloud cover affect the convective potential...if convection what storm mode is more favorable...rainfall rates/flash flooding potential in the stronger storms all remain in play. The next few afternoons CAMs all suggest some potential for low to possible moderate CAPE with the shear profile increasing through the weekend. There will be jet support both days this weekend and the remnant energy from Rachael moves through on Sunday providing extra focus. Profiles on Sunday suggest storm mode supporting organized convection bringing a low probability (<15%) of bigger hail and wind gusts over 55 mph. This may be easy to achieve in the 4 Corners where afternoon gusts may be well into 30s/low 40s already. The skinny CAPE profile is also suggestive of warm rain processes and this will bring a flash flood threat with rainfall rates of 1-2 inches per hour. Things look to taper off a bit on Monday as moisture decreases and hence CAPE decreases. Shear however stays strong with a 100+kt jet overhead in the downstream portion of the trough over the West. The forecast still has 1-2 inches of rain over the eastern Utah mountain ranges and the San Juans with a few peaks above 13K likely to get another dusting of snow. Confidence remains too low to put anything in a flood watch at this time.

The next system to impact the region is an early season winter storm as the cold-core Pacific Northwest low drops down through the Great basin before lifting to the northeast across the region Tuesday evening and Wednesday. This won't bring a lot of snow to the region, but we will likely see some winter driving conditions on the mountain passes with low visibilities and periods of slick roads. We will likely see snow down to 8,000 ft, but don't expect any accumulation below about 10,000 ft. Stay tuned for updates on this one too.

AVIATION /00Z TAFS THROUGH 00Z SUNDAY/

Issued at 529 PM MDT Fri Oct 9 2026

Isolated showers and thunderstorms will be dissipating with sunset then begin to reform tomorrow morning as moisture begins to increase in the moderately strong Southwest flow aloft. These strong winds aloft could lead to pockets of LLWS through tomorrow morning then mixing down gusts in the 25 to 35 mph range through the afternoon tomorrow. Showers and a few thunderstorms will also begin expand after sunrise and become more widespread as we go into tomorrow evening. Gusty outflow winds will be the main concern with VFR and low probability of ILS tomorrow afternoon.

HYDROLOGY

Issued at 1046 PM MDT Fri Oct 9 2026

A strong low pressure system off the Pacific Coast will begin to draw in tropical moisture associated with Topical Storm Rachel this weekend. This strong southerly fetch will draw anomalously high moisture content across the Desert Southwest and into eastern Utah and western Colorado. The chance for widespread precipitation increases Saturday evening into Sunday. Total precipitation forecasts range from 1 to 3 inches across high terrain, with highest amounts favoring the Uintas, Tavaputs and the Southwest San Juan mountains.

Embedded thunderstorms are also possible Sunday afternoon, increasing the threat for flash flooding across vulnerable terrain. While confidence in location and rainfall rates remain low at this time, the potential for rapidly rising rivers, streams, normally dry arroyos and slot canyons are possible Sunday through Monday.

Please follow the evolving forecast, especially if your plans including recreating or commuting across eastern Utah and western Colorado Sunday onward. Also, keep in mind weather potential above your location and upstream, particularly for those who reside below sensitive terrain like recent burn scars.

GJT WATCHES/WARNINGS/ADVISORIES

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