textproduct: Grand Junction

KEY MESSAGES

- Scattered to widespread precipitation chances persist today, with higher coverage of precipitation across southeast UT and southwest CO than previous days.

- Flash Flooding will continue to be possible as organized and training thunderstorms can produce heavy rainfall over a short period of time.

- Primary areas of concern for flash flooding will be those of increasingly saturated soils, recent burn scars, and steep terrain.

DISCUSSION

Issued at 1203 PM MDT Mon Aug 31 2026

SHOWERS AND THUNDERSTORMS TODAY:

Today looks to be our final day of widespread showers and thunderstorms from the current push of monsoonal moisture. Today's sounding shows a decrease in both precipitable water (PW) and instability. However, the PW value of 1.04 inches exceeds the 90th percentile for August 31st at GJT, which shows that atmospheric moisture is still abundant. The reduction in instability and persisting widespread cloud cover could act to dampen today's convection, mostly during the early afternoon. However, a shortwave trough, in addition to a bit of jet support and difluence aloft, will support more storms this evening even during the absence of surface heating. Many storms will efficiently produce rain, which could lead to localized areas of flash flooding from heavy rainfall. Primary areas of concern for flooding are recent burn scars, slot canyons, slick rock areas, creeks, streams, and other low-lying and flood-prone locations. Most of eastern Utah and western Colorado remains in a Flood Watch through midnight tonight.

DRIER TUESDAY THROUGH FRIDAY:

Atmospheric moisture will decrease tomorrow, leading to decreased precipitation chances. Afternoon convection will still be possible, particularly on Tuesday and Friday, but chances favor the higher terrain. High temperatures will gradually increase through the workweek, returning to near normal by Friday.

MOISTURE RETURNS THIS WEEKEND:

Guidance suggests a strong push of tropical moisture late in the workweek and into the weekend. The ECMWF Ens and GFS Ens are presently in relatively good agreement regarding the timing and magnitude of this moisture. However, changes with the tropical system activity in the Pacific could substantially alter this forecast, so be sure to stay tuned for updates on how this weekend's forecast develops.

AVIATION /18Z TAFS THROUGH 18Z TUESDAY/

Issued at 1148 AM MDT Mon Aug 31 2026

Scattered to widespread showers and storms return again this afternoon/evening. Precipitation chances will begin first at terminals along and south of I-70, with chances spreading northward into the late afternoon hours. Primary threats will be heavy rainfall, lightning, and gusty outflow winds. Heavy rainfall has the ability to reduce visibilities and drop conditions to MVFR at some locations. Additionally, under storm activity, cigs may fall below ILS breakpoints as has already been observed at KEGE this morning. Some terminals could see nocturnal convection, others will return to light and terrain driven patterns overnight. Cloud cover clears out into the early morning hours and the sun returns.

HYDROLOGY

Issued at 1203 PM MDT Mon Aug 31 2026

Anomalous moisture will remain in place across western Colorado and eastern Utah through tonight. Today's 18Z sounding from GJT shows that precipitable water exceeds the 90th percentile for today, and relative humidity remains elevated in the mid and lower levels of the atmosphere. Given the antecedent moisture from rainfall over previous days and already saturated soils in several sub-basins, rapid runoff and poor infiltration has become more likely in some areas. A Flood Watch remains in effect through Monday evening for most locations.

Flash flooding and debris flows are possible, especially over recent burn scars and susceptible terrain. Critical areas of concern within the Flood Watch include the Lee and Elk RX, Gold Mountain, Elk, Ferris, and Babylon burn scars, where hydrophobic soils have the ability to amplify peak flow under moderate rainfall rates.

Although drier air moves into the region tomorrow, lingering mid-level moisture and daytime heating will keep afternoon thunderstorms in the forecast for the higher terrain regions. Hence, a localized flash flooding threat remains.

GJT WATCHES/WARNINGS/ADVISORIES

CO...Flood Watch until midnight MDT tonight for COZ002-003-006>014- 017>023. UT...Flood Watch until midnight MDT tonight for UTZ022-025-027>029.