textproduct: Grand Junction

KEY MESSAGES

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

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

- Flood Watch in effect for SE Utah and SW Colorado Wednesday through Thursday with multiple rounds of heavy rain impacting burn scars, slot canyons and areas of susceptible terrain on already saturated ground.

- Temperatures run near to around 5 degrees below normal through the end of the week.

DISCUSSION

Issued at 1258 PM MDT Tue Sep 15 2026

STRONG TO SEVERE STORMS POSSIBLE TODAY:

Storms are already ongoing this morning across southeast Utah with storms beginning to fire over the western Colorado high terrain with daytime heating and spreading into some valleys. We remain plenty unstable and moist as evident in our 18Z GJT sounding with surface CAPE of around 1400 J/kg and a forecast surface CAPE around 2000 J/kg. Plenty of shear out there as well with 30 kts so enough to sustain updrafts. Like yesterday, we could see strong to potentially severe storms, capable of large hail and damaging winds in addition to heavy rain and frequent lightning. Hi res CAMs seem to indicate storm coverage and intensity ramping up late this afternoon into the evening hours. We remain in the favored right entrance region of the upper level jet giving us that dynamic forcing needed to support robust convection.

FLOOD WATCH WEDNESDAY AND THURSDAY:

A strong low pressure trough remains to our west with high pressure across the southeastern CONUS, keeping our CWA in the direct moisture feed from the south that stretches from the Baja across Arizona and New Mexico through the Four Corners and up into eastern Utah and western Colorado. PWAT anomalies will remain around 200 percent of normal through the end of the week with a surge in moisture Wednesday evening through Thursday afternoon where PWAT anomalies surge close to almost 300 percent of normal, mainly across southwest Colorado. Areas around SW Colorado have received 1 to 2 inches of rainfall based on reports over the last 24 hours so this area remains saturated. Storm coverage will become more widespread Wednesday and Thursday due to some robust shortwaves moving through Wednesday afternoon as well as another Wednesday night into Thursday. Given the surge in deeper moisture, already saturated ground from recent rains, and burn scars in the region...decided to issue a Flood Watch for portions of SW Colorado including the SW CO valleys and San Juan mountains from Wednesday afternoon through Thursday night. Also, issued a Flood Watch for portions of SE Utah from midnight tonight through 6 am Thursday. This includes the Babylon, Ferris, Gold Mountain and Elk burn scars in particular among other susceptible flood prone locales. Heavy rain is a near certainty with any storm that develops so other areas outside the Flood Watch could see impacts, but the Flood Watch is for where the best potential and highest confidence lies. Cannot rule out strong to severe storms as well given the dynamic forcing of the jet, instability and shear...but this may all depend on the amount of cloud cover as deeper moisture moves in Wednesday evening through Thursday night.

FRIDAY AND BEYOND:

Friday onward, forecast confidence decreases. Models are in poor agreement as to what happens once the West Coast trough ejects to the northeast, with some solutions building a ridge, and others developing a Rex Block over the Southwest. Ensembles do indicate a gradual drying trend, but keep PWATs of 100-150% of normal around through the weekend. That's enough to keep a chance of isolated to scattered terrain based showers and storms in the forecast. However as we've seen with this type of pattern in the past, models tend to be too quick to exit this moisture and we could see stronger storms possible along that moisture gradient as dry air tries to move in from the west. With abundant cloud cover and shower activity expected through the end of the week, temperatures will run near to around 5 degrees below normal.

AVIATION /00Z TAFS THROUGH 00Z THURSDAY/

Issued at 544 PM MDT Tue Sep 15 2026

Expect showers and thunderstorms through 04Z mostly north of I-70 and in the southern mountains with thunderstorms diminishing to isolated through the overnight over the higher terrain and showers becoming light and stratified through the mountains. Look for more active weather with thunderstorms and heavier showers to pick up after 18Z. Heavy rain and wet downburst with 50KT gusts are possible with these storms. The mountain TAF sites can expect periods below ILS breakpoints for low ceilings and reduced visibility with these storms.

GJT WATCHES/WARNINGS/ADVISORIES

CO...Flood Watch from Wednesday afternoon through Thursday evening for COZ018-019-021>023. UT...Flood Watch from midnight MDT tonight through late Wednesday night for UTZ022-028-029.