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 heavy rainfall will have the ability to produce 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 Thu Jul 16 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 forecast area this week. The ECMWF Ens and GFS Ens have consistently shown differences in the magnitude of the anomalies, with ECMWF Ens continuing to favor 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 through next week.

Today's afternoon convection has begun along the higher terrain, and will gradually increase in coverage through the afternoon. QPF favors the San Juan Mountains, where increased moisture has allowed for showers and storms during the preceding days. Elevated PoPs have more northward coverage today than the previous days during this period of increased moisture. However, areas that still have dry lower atmospheres may see more virga showers/rain not reaching the ground mixed with some showers producing measurable precipitation. Each day the moisture will advect further north/northeast, allowing for more widespread chances of showers and thunderstorms by this weekend.

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.

DECLINING TEMPERATURES:

Temperatures will gradually decrease for the remainder of the week thanks to increased cloud cover during peak heating. Guidance continues to favor another drop in temperatures next week, potentially leading to below-normal temperatures.

AVIATION /00Z TAFS THROUGH 00Z SATURDAY/

Issued at 528 PM MDT Thu Jul 16 2026

Stormy weather continues for the majority of the region. Most terminals (aside from HDN and VEL) may see rainfall this evening and/or tomorrow afternoon. Gusty outflow winds up to 35 kts will be possible, and higher elevation terminals, particularly ASE and EGE could occasionally drop below ILS breakpoints. Heavier rain could also drop vis to MVFR, though areas where this will occur are too uncertain at this time, and thus vis reductions have not been included in any TAF's.

HYDROLOGY

Issued at 1235 PM MDT Thu Jul 16 2026

An anomalous plume of moisture continues to rotate into Utah and western Colorado this afternoon, with a slight uptick compared to yesterday. The San Juans remain a bullseye in precipitation forecasts this afternoon and again on Friday, maintaining flash flood threats redeveloping each afternoon. However, available moisture is higher moving west into Utah, which leaves the potential for isolated storms to produce hourly rainfall rate of 1-2 in. Therefore, areas of concern remain unchanged from the previous forecast for this afternoon.

Storms over the last 24 to 48 hours have only helped prime lower levels of the atmosphere and saturate the ground where rain was observed. Several locations across southwest Colorado reported over 0.5 inches of rain within 30 minutes during yesterday's convection; which is more than sufficient to create issues in our steep, rocky terrain already susceptible to flash flooding. This environment also triggers heightened awareness over recent (or actively burning) fires, due to the burnt ground's inability of absorbing moisture under heavy rainfall. As such, we continue to emphasize the potential for flash flooding and debris flows in this regime.

As a reminder: 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.