textproduct: Grand Junction

KEY MESSAGES

- Expect terrain-based showers and thunderstorms each afternoon this week, favoring the San Juans, but spreading north by the weekend.

- Localized heavier showers and storms create a risk of flash flooding and debris flows in vulnerable terrain, including areas near and downstream of burn scars.

- Daytime highs cool throughout the week, returning to near- normal for most areas by Friday.

DISCUSSION

Issued at 1235 PM MDT Wed Jul 15 2026

DAILY SHOWERS AND THUNDERSTORMS:

Persistent high pressure aloft keeps a plume of moisture over much of the West through at least this weekend, potentially beyond. Guidance keeps the most moisture rich part of this plume (in terms of PWAT anomalies) to our west, but ensembles place PWATs of 130-200% of normal over our CWA this week. The ECMWF Ens and GFS Ens have consistently shown differences in the magnitude of the anomalies, with ECMWF Ens favoring a much more moist setup with max PWATs closer to 200% at times. This moisture brings daily chances of showers and thunderstorms in the afternoon and evening. These chances favor south of I-70 today, but over the next few days coverage of chances spread north across the CWA. Storms moving across the San Juan Mountains this afternoon have produced measurable precipitation and wetting rain, but more northern areas receiving their first push of moisture could initially see a mix of rain reaching the ground and virga/gusty outflow winds. While moisture is a relief for drought conditions, it also creates a risk of flash flooding and debris flows, including over the burns scars of the Gold Mountain, Ferris, and Babylon fires. The hydrology section below discusses this risk in greater detail. These storms can develop quickly, so be sure to monitor the forecast and have a way to receive weather alerts, especially if you are visiting or reside below terrain that is vulnerable to flash flooding, including downstream of active fires.

Temperatures should fall by at least a few degrees during the remainder of this week thanks to increased cloud cover during peak heating. Guidance continues to favor another drop in temperatures next week, potentially leading to widespread below normal temperatures. However, this is largely dependent on how the high pressure aloft shifts.

AVIATION /18Z TAFS THROUGH 18Z THURSDAY/

Issued at 1143 AM MDT Wed Jul 15 2026

Expect mostly VFR conditions through the TAF period, the exception will be brief periods of MVFR associated with thunderstorms at TAF sites along and south of I-70 between about 20Z and 03Z. Winds in the vicinity of any showers or thunderstorms will be variable gusting 35 to 50 kts. Otherwise, look for light winds generally westerly to northerly through the afternoon becoming light drainage winds after 03Z.

HYDROLOGY

Issued at 1235 PM MDT Wed Jul 15 2026

An anomalous plume of moisture continues to rotate into Utah and western Colorado this afternoon, as an elongated area of high pressure shifts into the southwestern CONUS. For today, steering winds overhead are northerly, providing a unique storm motion for the GJT forecast area. In addition, our southern zones and most of eastern Utah contain higher amounts of moisture, so as storms generally build and shift south, they're moving into juicier environments.

Even though this source of moisture is a great relief to the drought stricken West, excessive rainfall returns the concerns of flash flooding and debris flows over recent (or even on going) burn scars. 18Z's sounding also shows weak flow throughout the atmospheric column, which will result in slow moving thunderstorms this afternoon. The combination of increased moisture and slow storm motion further elevates the concern for excessive rainfall in localized areas. The San Juan's are a bullseye in precipitation forecasts over the next several days, maintaining flood threats redeveloping each afternoon. Due to the prolonged period of anomalously high moisture, over areas with sensitive burn scars, we want to emphasize the potential for flash flooding and debris flows in this regime. We're expecting an uptick in moisture content across the entire region on Thursday, which favors a higher likelihood of wetting rain with bursts of heavy rain in localized storms.

For 2026 fires, we have yet to test their susceptibility to handle rainfall. Therefore, we want to increase our messaging of the potential hazards at play downstream nearby fires. Keep an eye on our forecasts through the end of the week and stay tuned for updated hydro alerts if visiting or if you reside below vulnerable terrain to flash flooding and/or debris flows. Storms across the west develop quickly, leaving little room for lead time in flashy terrain.

GJT WATCHES/WARNINGS/ADVISORIES

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