textproduct: Grand Junction

KEY MESSAGES

- Shower and storm chances increase today, with higher chances overnight into tomorrow morning.

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

- Moderate to heavy rainfall could lead to localized flash flooding, rockfalls and mudslides at times this week.

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

DISCUSSION

Issued at 1138 AM MDT Sun Sep 13 2026

COOLER AND WETTER PATTERN THIS WEEK:

Residual moisture and daytime heating will result in terrain-driven showers and storms this afternoon and evening. The jet associated with a low pressure in the PacNW has spread over the region. This means there is some shear present, which could support a few stronger storms, especially across the northwest half of the CWA. This evening there should be a transition to more stratiform with embedded storms.

As that low pressure passes to our north southwest flow will advect a pocket of deep moisture into the area tonight. PWAT values peak over 200 percent. Therefore expect the coverage of precipitation to increase during this surge. The high-res models focus showers north of I-70 early in the night then south of I-70 late in the night, which may be due to upper level jet forcing and a weak front. Periods of moderate to heavy rain are possible and could result in localized flooding, rockfalls and mudslides. Widespread showers are expected south of I-70 tomorrow morning, while the north starts clearing out. The moisture may somewhat decrease, but it will still be sufficient for redevelopment through out the day. The intensity and coverage will depend on the instability. So places that clear out have higher chances of storms in the afternoon. The jet will still be overhead so some storms may become strong to severe.

The area remains in southwest flow aloft as the first low pressure tracks over the Midwest and another low drops into the PacNW. This will ultimately keep the moisture in place through at least mid week, so expect the chances for showers and storms to continue. On Wednesday the models are hinting that a subtle wave moves in from the southwest. If this were to happen it would certainly be a focus for showers and storms especially given the moisture will still be around. Late in the week, the models are now agreeing that the second low pressure cuts off in the PacNW and northern Great Basin. Model performance is typical poor for these cut off lows, mainly how long they stick around. This lowers confidence in the forecast late in the period. As it stands now though this period looks to be active due to the low pressure and moisture.

AVIATION /18Z TAFS THROUGH 18Z MONDAY/

Issued at 1147 AM MDT Sun Sep 13 2026

Showers and storms will highlight the forecast for this TAF package. Storms have already begun firing along the Western Slope and will continue to become more widespread later this afternoon and especially during the overnight period. Localized heavy rainfall impacting visibility along with lightning and gusty outflows will be the primary threats for aviators. MVFR conditions may be possible where visibilities deteriorate. Winds will be breezy this afternoon, with some locations holding on to the higher speeds well into the overnight period. Gusts are forecast to be 20-30 kts. Precipitation chances will continue to be around for much of Monday as well.

GJT WATCHES/WARNINGS/ADVISORIES

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