textproduct: Grand Junction

KEY MESSAGES

- Monsoonal moisture and a robust disturbance will cause precipitation chances to become more widespread today.

- Heavier rainfall today could lead to localized flash flooding over burn scars and susceptible terrain.

- Temperatures gradually cool off for the weekend and into next week with a warmup late in the week, remaining above normal.

DISCUSSION

Issued at 1043 AM MDT Sat Aug 22 2026

ACTIVE THIS WEEKEND:

A line of showers and isolated thunderstorms along the leading edge of a shortwave are moving through eastern Utah and progressing into western Colorado this morning, which models are not picking up on or initializing well with. This line was fairly active through the early morning hours in eastern Utah. This is likely due to added upper level support from a low pressure trough moving into the Pacific Northwest, allowing the flow to shift to more southerly and therefore pull up deeper monsoonal moisture last night into this morning and act on the instability already in place. This trough is also nudging the high pressure ridge eastward. Deterministic models are fairly consistent in showing this deeper moisture plume working its way across our CWA today with PWAT anomalies jumping to 160 to 180 percent of normal. Where the models differ is in terms of how robust or widespread the convection will be. The GFS is not as widespread but the hi-res CAMs, particularly the HRRR, seem to indicate a later start to afternoon convection likely due to this morning convection and cloud cover. After this morning wave moves eastward, afternoon convection looks to refire off the higher terrain, with coverage and more robust convection increasing late this afternoon into the evening hours as a robust shortwave moves through the flow providing added forcing and support. CAPE will be sufficient with around 500 to 800 J/kg with mixing ratios in the 5 to 6 g/kg range which is sufficient for heavy rain potential with any storms today. With the better steering flow, there is a good chance storms will impact some lower valleys as well late in the day. The deeper moisture in place today with the added forcing provided by the robust shortwave will increase flash flooding and debris flow concerns, especially over burn scars and susceptible terrain. Be weather aware and make sure you have a way to receive watches and warnings. Cannot rule out some convection continuing through the overnight hours but most activity should wind down by midnight or shortly after.

On Sunday, the Pacific Northwest trough will have lifted out into Canada with the robust shortwave already out into the Plains, leaving us in a westerly flow as the shortwave and trough allow the high to lay over. We will still see residual moisture in place with another day of afternoon showers and storms, but without the added forcing, storms should be mostly confined to the high terrain. Flash flooding is still a concern over burn scars but looks to remain more localized on Sunday as there isn't a real focus for where the better chances reside. Highs this weekend will be cooler than previous few days with temperatures around 5 degrees cooler but still remaining 5 degrees above normal.

NEXT WEEK:

The high pressure and above normal moisture will remain in place through this coming week with the high slowly meandering back to the west across the Desert Southwest (south of the Four Corners) by mid to late week. Some shortwaves will move through the flow across the north up and around the high pressure through the Northern Rockies, providing a little lift for some afternoon convection each day but the focus seems to be over the high terrain with quite a bit of uncertainty as to the quality of this moisture with the heavy rain potential looking more localized as this moisture gets recycled under the high. PWAT anomalies slowly trend downward as this high shifts westward and drier air is pulled into the Great Basin. Daytime highs hold steady as we move into the coming week with highs around 5 degrees above normal and gradually increase towards around 5 to 10 degrees above normal by late week.

AVIATION /18Z TAFS THROUGH 18Z SUNDAY/

Issued at 1150 AM MDT Sat Aug 22 2026

Isolated to scattered showers and thunderstorms are ongoing around the region. Coverage of convection will increase through the afternoon with showers and storms most likely to occur between 18Z to 02Z. Primary concerns with convection are lightning and brief periods of heavy rain producing MVFR conditions. Strong outflow winds 35 mph or greater could be possible near some showers and thunderstorms. Some of this activity may linger into the overnight hours, mostly over the high terrain.

GJT WATCHES/WARNINGS/ADVISORIES

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