textproduct: Grand Junction

KEY MESSAGES

- Terrain based showers and thunderstorms will continue Tuesday. Gusty outflow winds, lightning and especially dry lightning will remain threats.

- Available moisture increases through the week with an uptick in convection and precipitation coverage and intensity expected Wednesday onwards.

- Wednesday evening through Friday morning will see a significant threat for heavy rain and training storms leading to areas of flash flooding, and debris flows from fire scars. - Above normal temperatures will gradually cool closer to normal with a cooling trend brought on by monsoonal moisture Wednesday and beyond.

DISCUSSION

Issued at 1034 PM MDT Mon Aug 10 2026

Satellite imagery shows a classic monsoonal pattern with a Four Corners high wrapping moisture up out of Arizona into Utah and the Great Basin before turning east across Utah and into Colorado. This pattern doesn't tend to produce heavy rains across eastern Utah and Western Colorado because the Wasatch Range taps the moisture of the lower levels leaving the mid to high level moisture to push east, but this pattern can produce significant lightning with only light rain. Otherwise the pattern is controlled by high pressure that the models are positioning across the southeast, but satellite imagery puts it more over southern Louisiana/southeast Texas which is more favorable for pushing the moisture off the Gulf up into West Texas, New Mexico and ultimately southern Colorado. Look for pwats ranging from 3/4 inch to an inch across the region tomorrow with the heavier moisture to the west mostly over eastern Utah. Though we are nor expecting heavy rain from these showers and thunderstorms, be aware that the major fire scars can produce significant flash flooding and debris flows with only a half inch of rain falling in under a half hour. Always be alert to the weather and your surroundings that may pose possible hazards. Flash flooding can occur miles from the thunderstorm.

Tomorrow will see low pressure forming off Southern California that will develop into a trough along the West Coast by Wednesday. This will bring a more south-southwesterly flow up through Arizona into eastern Utah and Western Colorado with a more direct path for deeper moisture to move up into the region Wednesday night and Thursday with pwats peaking at an inch or more across much of the region. This is when we are likely to see areas of heavy rain and training thunderstorms, especially along the southern to southwestern exposures of rising terrain. SPC has the entire region under marginal (>5%) chances for excessive rainfall with slight (>15) along the Divide extending west across the higher terrain of central and southern Colorado, and to the south over southeastern Arizona into west central New Mexico. Would not be surprised if these two areas of higher probability for excessive rain connect in the next day or two. This will be the greatest threat for flash flooding from heavy rains and debris flows from the fire scars. Stay alert to changes and updates to the forecast over the next few days.

Beyond a few days, forecast confidence fall off as the models, and even the ensembles are diverging in their solutions. They are in agreement with the flow aloft becoming more southwesterly Friday which tends to dry out the region, but the European models push the high back to to the east keeping the Southwest under a drier southwesterly flow while the GFS/GEFS models keep the high farther west over Texas with a more southerly flow across Arizona and New Mexico to bring a return of the deeper moisture going into early next week.

AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/

Issued at 1145 PM MDT Mon Aug 10 2026

Outside of light showers at KDRO and KEGE lasting through the next hour or so, showers and thunderstorms have mostly ended across the region. By 07Z no impacts to TAF sites are expected from precipitation activity. However, shower and thunderstorm activity begins again tomorrow afternoon, bringing potential for gusty outflow winds and brief periods of MVFR conditions some sites. Tonight winds will become light and terrain driven, and VFR conditions are expected to prevail.

GJT WATCHES/WARNINGS/ADVISORIES

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