textproduct: Grand Junction

KEY MESSAGES

- Shower and storm chances increase Sunday, and peak in coverage by Monday, bringing in widespread cool, wet, and unsettled weather.

- There is a chance for strong storms over the next few days capable of producing hail, gusty wind and heavy rainfall.

- Daytime highs on Sunday will be 5 to 10 degrees above normal, before a shift to cooler temperatures by Monday.

DISCUSSION

Issued at 917 PM MDT Sat Sep 12 2026

SCATTERED STORMS SUNDAY:

Shower and storm coverage increases tomorrow as the next strong push of moisture begins to move in. PWATs continue to climb, with values upwards of 200% of normal, with the likely chance of exceeding the 75th percentile and approaching, if not surpassing the max values for mid September.

COOLER AND WETTER PATTERN MONDAY AND BEYOND:

By Monday, a deep trough begins to push into the PacNW. Due to cyclonic flow around a low, southwesterly flow will be favored over the southwestern CONUS. This means subtropical moisture will be pushed further inland, centering the strong plume of moisture over our CWA. PWATs continue to be forecasted over the 75th percentile for this time of year, which will be enough to prompt our next chance for widespread showers and storms.

Monday is the peak of the moisture, but it may be so much that we end up cloudy therefore inhibiting instability. If that happens we will see more stratiform showers. However, it is worth considering the dynamic forcing at play during this time period. Firstly, Sunday night into Monday will see a cold frontal passage which will include pockets of frontogenesis. Secondly, by Monday we are expected to be under the right entrance region of an upper level jet. This may enhance the lift across the area. Also, the jet may provide wind shear that could support strong to severe storms capable of hail and damaging winds. Given the moisture there is the potential for heavy rainfall as well. Cell training and or any severe storm could lead to localized flash flooding.

Despite the shortwave ejecting out over the Northern Plains the models show a trough remaining in place across the PacNW as well as the upper level jet overhead. The highly anamolous moisture also pushes east, but there is still sufficient moisture lingering across the area. The shear and moisture may once again could support strong storms. The coverage is more uncertain with the lack of forcing, so the convection may be more terrain driven. Confidence decreases mid week as the second PacNW trough either swings through or becomes a cut off low to our west.

Look for daytime highs to cool down Monday and beyond due to that aforementioned frontal passage as well as the cloud cover and potential showers.

AVIATION /00Z TAFS THROUGH 00Z MONDAY/

Issued at 522 PM MDT Sat Sep 12 2026

Some showers are passing through the region this evening, though impacts to terminals are expected to be minimal, if anything at all. As such, VFR conditions persist through tomorrow morning. Storms redevelop and become more widespread tomorrow beginning around 17 UTC. The terminals most likely to be impacted are GJT, RIL, MTJ, TEX, and GUC. Brief drops in visibility to MVFR cannot be ruled out, though terminals are expected to remain above ILS breakpoints. Otherwise, gusts of 20-28 kts are expected to develop tomorrow afternoon for most, if not all terminals.

GJT WATCHES/WARNINGS/ADVISORIES

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