textproduct: Grand Junction

KEY MESSAGES

- Flash flooding will be possible for the coming days as record moisture propagates through eastern Utah and western Colorado. - Flood Watches remain in effect for SE Utah and SW Colorado today through Thursday.

- Impacts from flash flooding could observed at multiple locations across the CWA, with the highest risk likely around slot canyons and burn scars.

DISCUSSION

Issued at 1050 PM MDT Wed Sep 16 2026

ABUNDANT MOISTURE THROUGH THURSDAY:

We remain under a deep plume of sub-tropical moisture with a robust low pressure trough to our northwest and high pressure to the southeast. PWAT anomalies are near 200 percent of normal and are expected to increase overnight through Thursday morning across southwest Colorado upwards of 250 to almost 300 percent of normal. At this magnitude, PWAT values are likely to break records. Much of southeast Utah and especially southwest Colorado has seen plenty of rainfall and remains saturated. Currently, this area is becoming more stratiform with robust thunderstorm development focused on the leading edge of that moisture mainly along and north of I-70 where skies weren't as clouded over. This area remains in the right entrance region of the upper level jet so plenty of dynamics to support updrafts and thunderstorm activity through the overnight, although most hi-res CAMs are showing this area eventually stratiforming out by Thursday morning. We are still seeing moderate rainfall rates out of the stratiform rain showers with heavier rates where stronger convection is occurring and this will be the case through Thursday. Driving much of this thunderstorm activity is a robust shortwave moving through tonight as well as remnant outflow boundaries from previous convection helping to sustain thunderstorm activity through the overnight hours.

Expect this shower activity to continue through the day Thursday with perhaps more stratiform mode to shower activity with embedded thunderstorms where breaks occur and can realize the instability. Due to overnight shower and storm activity, anticipate that abundant cloud cover Thursday morning may lead to this type of scenario. Regardless, robust convection is still possible with flash flooding concerns due to already saturated soils, especially across southwest Colorado. Therefore the Flood Watch remains in effect through Thursday night. The hail and wind threat though should be less as the atmosphere is saturated with hydrologic threats taking precedence.

FRIDAY INTO THE WEEKEND AND BEYOND:

By Friday, the moisture pool driving this wet pattern rapidly diminishes. However, even with this decrease in moisture, we remain confident that the majority of the region will still see above normal PWATs through the weekend with scattered storm coverage. Friday will be in the transition period as the low pressure begins to track eastward and lifts across the area. Given the drier air advecting from the west with moisture still in place, we could see stronger storms on the periphery with more sun to act on the instability and moisture in place. However, by the weekend, storm activity should become less pronounced with scattered coverage. By the end of the weekend, storm activity looks to be mostly confined to the higher terrain as convection will mainly be driven by orographics.

Beyond the weekend, models indicate some shortwave ridging providing a bit of a break in the active stormy pattern Sunday through Monday but this looks short lived as models are indicating another low pressure trough moving into the Great Basin and increasing storm coverage once again early to mid next week.

AVIATION /06Z TAFS THROUGH 06Z FRIDAY/

Issued at 1129 PM MDT Wed Sep 16 2026

Widespread light to moderate rain showers with thunderstorm activity and pockets of heavier rain on the leading edge of moisture across the central and northern portions of the area is currently ongoing late this evening. Gusty outflow winds and heavy rainfall will generate MVFR conditions in any storm. Precipitation will become more widespread and steady overnight continuing into the morning hours. The mountain TAF sites can expect periods of low ceilings and reduced visibility with these storms along with areas of terrain obscuration. Showers are expected to be more persistent Thursday with embedded thunderstorms possible. Shower and thunderstorm activity is expected to become more isolated by sunset with improving conditions.

HYDROLOGY

Issued at 1050 PM MDT Wed Sep 16 2026

HiRes guidance continues to suggest stratiform rain bring the dominant storm mode for the next 24 hours with embedded thunderstorm activity. A few embedded stronger cells should not be ruled out, which have the ability to produce localized heavy rainfall. Soils have also been allowed to significantly saturate over the past few days, which will lead to a lack of absorption in many places. Therefore, with this period of record moisture (for this time of year), it's safest to assume that flash flooding will be a possibility across most to all portions of the CWA through at least Thursday. This is, as usual, especially of concern for vulnerable areas like slot canyons and burn scars. Additionally, QPF for multiple forecast cycles continues to highlight the southern slopes of the San Juans and into the Animas and San Juan River Basins where 48-hour totals are exceeding 2 inches. As a result, southern portions of the CWA are in a Flood Watch for portions of the next 24 hours. Stay aware of road conditions, avoid locations prone to flash flooding, and report flooding or other weather impacts to local law enforcement.

GJT WATCHES/WARNINGS/ADVISORIES

CO...Flood Watch through Thursday evening for COZ018-019-021>023. UT...Flood Watch until 6 AM MDT Thursday for UTZ022-028-029.