textproduct: Grand Junction

KEY MESSAGES

- Moisture begins to increase today, with peak coverage expected Thursday.

- Localized heavy rainfall may prompt flash flooding and debris flows, especially around burns scars.

- Temperatures begin a cooling trend through the end of the work week, into the weekend.

UPDATE

Issued at 1152 AM MDT Wed Aug 12 2026

A Flood Watch has been issued for forecast zones that encompass the northwestern and southwestern San Juans until midnight. Localized heavy rainfall may prompt flash flooding and debris flows, especially around recent burn scars. Continue to be weather aware and have multiple ways to receive watches and warnings.

DISCUSSION

Issued at 1025 AM MDT Wed Aug 12 2026

PRECIPITATION CHANCES THROUGH THE END OF THE WEEK:

The current synoptic level pattern is characterized by a high pressure dome to our east, with troughing dominating the West Coast. This will allow flow aloft over the Desert Southwest and Southern Great Basin to transition to a more southerly-southwesterly regime. Because of the clockwise circulation associated with high pressure systems, this a prime setup for moisture advection. Recent sounding profiles have been depicting consistent long, skinny CAPE profiles which are indicative of favorable precipitation rates. Today, saturation down to the surface is expected, with widespread showers and thunderstorms in the afternoon, and wetting rains across the higher elevations. This will lead to an increased threat for flash flooding and burn scar debris flows today and Thursday.

By Thursday, shower and storm coverage is expected to peak. Hence, chances for heavy rains, flash flooding, and debris flows also peaks then. During these monsoonal patterns, some uncertainties can present themselves when it comes to the forecast...

1. Cloud Cover

With these setups, morning cloud cover frequently lingers, much like we've seen over the past few days, and will serve as a primary driver for afternoon storm evolution. Robust daytime heating will support more convective thunderstorm development. Conversely, persistent cloud cover will limit instability, favoring a shift toward broader stratiform showers. Lingering cloudiness will also delay convective initiation, pushing storm development deeper into the afternoon. Therefore, a lot can be dependent on how cloud cover pans out for the day.

2. Lift

Storms will likely initialize along the higher terrain over the next few days, which is typical for our CWA. However, subtle shortwaves rotating around the edge of the upper level high could supply additional mid-level lift. Lower confidence remains regarding the precise timing and impacts of these impulses and lingering outflow boundaries, creating uncertainty in convective coverage and evolution once storms track off the ridges.

With all that being said, confidence is high that we're moving into a wetter period for the latter half of the week and even into the weekend.

QUICK NOTE ON TEMPERATURES:

Temperatures begin to cool a few degrees each day as showers, storms, and cloud cover begin to prevail. By Friday, daytime highs will be below normal, a welcome relief from the previous stretch of hot temperatures.

AVIATION /18Z TAFS THROUGH 18Z THURSDAY/

Issued at 1144 AM MDT Wed Aug 12 2026

Storms are expected to develop region-wide today. Cigs may periodically fall below ILS conditions at ASE, EGE, RIL, and TEX as a result. Less confidence exists in if rainfall will be heavy enough to reduce vis to MVFR or lower. Storms will continue into the late evening and potentially through the early portion of the night. Gusty and variable outflow winds from storms could pass over any terminal. Most of these winds should be capped at 25 kts, but a few stronger gusts cannot be ruled out.

HYDROLOGY

Issued at 1152 AM MDT Wed Aug 12 2026

Moisture chances become more widespread today and peak in coverage by Thursday. Model guidance suggests heavy rainfall from thunderstorms and/or training storms is possible this afternoon and into the late evening hours. With that being said, a Flood Watch has been issued today for forecast zones that include the northwestern and southwestern San Juans. This also includes recent burn scars and steep mountain corridors in that area. This Flood Watch goes until midnight tonight. Continue to stay weather aware and have multiple ways to recieve watches and warnings.

GJT WATCHES/WARNINGS/ADVISORIES

CO...Flood Watch through this evening for COZ018-019. UT...None.