textproduct: Grand Junction

KEY MESSAGES

- Showers continue through Friday night. Lower chances of precipitation Saturday afternoon.

- Flooding/flash flooding concerns increase Sunday into Monday, especially for areas that have saturated soils from last week's rain. A Flood Watch remains in effect.

- Winter weather highlights have been issued for the San Juans and central Colorado mountains for accumulating snow Sunday morning through Monday evening.

DISCUSSION

Issued at 1000 PM MDT Fri Oct 30 2026

RAIN SHOWERS FRIDAY NIGHT AND SATURDAY EVENING:

A band of rainfall driven by a transient shortwave is steadily moving through the region tonight. Impacts will be minimal, though we have seen a stronger embedded thunderstorm or two develop, so don't rule out a few stronger outflow gusts. Otherwise, rainfall is steady and light. Per CAM's, the line of showers will continue northeastwards before departing the CWA late Saturday morning, making way for a relatively calm Saturday afternoon thanks to a "dry" spell. We're using the term "dry" very lightly as PWAT's will still be about 150% of normal (give or take 50% depending on which ensemble you listen to). This is enough to produce a few isolated showers across the region, so don't be surprised if you see a brief bout of rainfall during the afternoon hours. For most of the region though, little more than cloudy skies is to be expected through 6:00 PM MDT. After 6:00 PM, the upper-level jet strengthens overhead, which could produce a few stronger thunderstorms south of US-50 which may bolster a very slight flash flood risk should localized heavily rainfall track over vulnerable areas. As things stand now though, impacts are expected to be minimal and/or very localized.

RAINFALL, SNOWY MOUNTAINS, AND POTENTIAL FLOODING:

A robust Atmospheric River arrives on Sunday bringing well above normal amounts of moisture for this time of year across the Desert Southwest. Guidance continues to show precipitation arriving at the Four Corners region Sunday before sunrise and spreading northeastwards throughout the morning. The ECMWF Ens is running wetter than the GFS Ens for this storm with PWAT's about 0.1-0.25 inches higher in the former regionwide (and as a result, similar margins regarding QPF). So, we do still lack some confidence on the exact magnitude of precipitation accumulations. As far as the NBM is indicating though, areas along the US-160 corridor east of Cortez have a 50-70% of seeing 2 or more inches of rainfall. At higher elevations in the San Juans, QPE is expected to sit over 3 inches in most areas. Considering the notable rainfall these same areas experienced last week, flooding concerns are back on the table, and a Flood Watch is in place. More in the Hydrology section below.

We mentioned 3 or more inches of QPE in the San Juans with this storm system, but much of this water is expected to come down as snow as cold air underneath the passing trough moves overhead. Temperatures will begin to be more noticeably affected beginning near mid-afternoon Sunday as high temperatures are stunted, reaching only into the low-to-mid 50's for valleys and the 30's to low-40's for most mountain locations (with some areas unlikely surpass freezing during the day). Cold air advection will continue throughout the night as well as the storm progresses. What this means for precipitation across the region is that snow levels will begin relatively high Sunday afternoon (around 11,000 feet) before descending over the next 24-36 hours, likely reaching as low as 7,500 to 8,000 feet. Snow ratios wouldn't be overly impressive given the anticipated temperatures, but given the amount of available moisture we'll be experiencing, sufficient factors are in place for well over a foot of snow in the San Juan mountains. Confidence is low on a range of snow accumulations given the transition from rain to snow for most areas, but 14-20 inches currently looks like the most likely range above 11,000 feet and much more variable accumulations below this elevation. In the central Colorado mountains, locations above 11,000 feet are in line for 10-15 inches of snow, meanwhile the Grand Mesa and Flat Tops, considering their lower elevations, are facing 6-12 inches. As a result, Winter Weather highlights are in effect Sunday and Monday. In passes, snow may be slushy given the lower snow ratios, so be mindful should you be traveling through the mountains Sunday or Monday.

AVIATION /12Z TAFS THROUGH 12Z SUNDAY/

Issued at 520 AM MDT Sat Oct 31 2026

A few lingering shower across the region will diminish by about 15Z with mountain TAF site ceilings below ILS breakpoints during this time. Look for isolated showers and thunderstorm to reform on the higher terrain after 18Z. Chances are still too low to call these out in the TAFs. Look for the next round of showers and thunderstorms to move in the the region from the west and southwest after 06Z becoming widespread across much of he region by 12Z. Winds remain generally light and terrain driven through the period.

HYDROLOGY

Issued at 1054 AM MDT Thu Oct 29 2026

Low pressure begins to dig southward from the PacNW on Friday, tapping into a fetch of Pacific moisture that will evolve into an atmospheric river streaming into the Desert Southwest this weekend. Showers and thunderstorms will develop Friday and Saturday, but totals will remain on the lower side. However, a few thunderstorms could produce impactful downpours on saturated soils left over from last weekend's historic flooding.

Deeper moisture develops Saturday night into early Sunday. This is expected to produce widespread rainfall with stronger rain rates across southeast Utah and southwest Colorado Sunday and Monday, mostly below 10,000 feet. Some area rivers are currently forecast to go into action stage. Additionally, a growing concern lies in the potential for runoff around steep terrain in the region. This could produce rock, mud, and debris flows onto roadways, as well as flash flood-prone burn scars, washes, slot canyons, and arroyos. Current guidance supports 1 to 3 inches of rainfall for far southeast Utah and portions of southwest Colorado. As a result, a Flood Watch has been issued for 5 AM Sunday through 11 AM Monday.

Outdoor enthusiasts, motorists, and residents of areas recently impacted by flooding are encouraged to remain tuned into the forecast in the coming days.

GJT WATCHES/WARNINGS/ADVISORIES

CO...Winter Weather Advisory from noon Sunday to 6 PM MDT Monday for COZ009-010-012-013. Winter Storm Watch from Sunday morning through Monday morning for COZ018-019. Flood Watch from late tonight through Monday morning for COZ019-021>023. UT...Flood Watch from late tonight through Monday morning for UTZ022-028-029.