textproduct: Grand Junction

KEY MESSAGES

- Showers and thunderstorms expected in northeast Utah and northwestern Colorado this afternoon.

- A warming trend will continue. Triple digits will remain confined to the Four Corners and low desert valleys.

- Monsoonal flow begins to appear in model outputs this weekend.

DISCUSSION

Issued at 1223 PM MDT Tue Aug 18 2026

An elongated high pressure system persists to our south today, placing a stream of mild moisture across the northern portions of our CWA. Here, some showers have already developed with some isolated thunderstorms expected to form this afternoon over the eastern Uintas and possibly into the Yampa River Basin. Impacts should be minimal with these storms aside from a few gusty outflow winds given the relatively dry near-surface layer. Even as the ridge builds tomorrow and into Thursday, moisture remains trapped west of the Rockies, maintaining daily chances of showers and thunderstorms focused over the high terrain. There's no indication that the low-level atmosphere will come close to saturating through the work week, so heavy rainfall potential is fairly low. However, given the weakening flow aloft, storm motion could come to a screeching halt by Thursday, which means the potential for a localized flash flood concern over vulnerable areas is non-negligible. Still, this is an unlikely scenario. What is likely with this building ridge is the return of high temperatures ~10 degrees above normal, leaving some low-lying areas to hit triple digit highs once again.

Into the weekend, deterministic models are suggesting an omega block forms across the country, leaving us firmly underneath southwesterly flow. Under this, there is an emerging signal of another round of monsoonal moisture working its way into the Great Basin. At this time, indications are that the plume is not overly strong nor wide in areal extent, and so it's iffy on how concerning heavy rain impacts could be. However, even if the center of the moisture plume skirts around us, we are expecting some amount of an uptick in storm coverage. Further speculation on impacts will depend on storm motion, the potential for training storms, and instability resulting from cloud cover (or the lack thereof), all of which are too early to speak on with confidence at this time. Once hi-res model guidance becomes available in a couple days, these details will become clearer. Until then, keep this weekend in the back of your mind as the next potentially potent weather day.

AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/

Issued at 1143 AM MDT Tue Aug 18 2026

VFR conditions are expected to prevail at most terminals this afternoon. A weak disturbance is producing more ample cloud cover at the mid levels today. Breakpoint conditions are unlikely. Introduced PROB30 showers at KHDN for the non zero chances of some light rain there this evening as this weak boundary settles over northeast UT and northwest CO. Did not include KVEL at this time. Afternoon winds will gust to around 25 mph across the region. The shower activity north of I-70 could produce some stronger outflow gusts this evening. Skies will clear out early Wednesday morning and winds will return to slack night time drainage conditions.

GJT WATCHES/WARNINGS/ADVISORIES

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