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 944 AM MDT Wed Sep 16 2026

WET WEDNESDAY + THURSDAY:

Another surge of sub-tropical moisture is forecast to enter the region today and stick around for the next 24-48 hours, making for an even wetter environment than observed over the past few days. Persistent flow will continue to dominant over eastern Utah and western Colorado. Additionally, PWATs are forecast to be upwards of 300% of normal in some places, particularly focused on the southwestern corner of Colorado. At this magnitude, PWAT values are likely to break records.

With this much moisture, cloud cover will certainly be around for the next few days, keeping the daytime highs on the cooler side. While on the topic of cloud cover, it is important to note that cloud cover has the ability to dictate storm mode. Increased morning cloud cover is indicative of more stratiform rain showers, whereas less morning cloud cover can lead to an eventful afternoon with more intense thunderstorms. Both of these outcomes could be observed over the next 24-48 hours, or even a mix of both. While we often talk about stratiform rainfall being less threatening to flash flooding concerns due to weaker rainfall rates, that is not quite the case through tomorrow. For one, the lower levels are significantly saturated from previous days rainfall in most places. This will lead to efficient rainfall and minimal absorption by soils. We've already seen some vulnerable locations produce flash flooding and debris flows with weaker rainfall rates, which is an indication that there is little room left for the land to take on more water. On the other hand, just because stratiform showers may dominate does not mean that embedded stronger cells cannot develop. There are upper level dynamic forcing parameters in place that could lead to strong updrafts and localized heavy rainfall. With all that being said, the hail and wind threat will be on the downturn as hydrologic threats take precedence. Refer to the hydrology section below for more detailed information about the threat.

FRIDAY + 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 the low pressure beginning to track eastwards, storm activity should become less pronounced. Bottom line is that storm chances will be around Friday, but more scattered in nature. 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.

AVIATION /12Z TAFS THROUGH 12Z THURSDAY/

Issued at 549 AM MDT Wed Sep 16 2026

A convective shower/thunderstorm pattern will be anchored across the area through the next 24 hours and impacting all TAF sites. Through the morning hours, a bulk of the storms will lift up across northern TAF locations as storms move southwest to northeast. Gusty outflow winds and heavy rainfall rates will generate MVFR cigs/vsby at times in any storm. Thunderstorms and heavier showers are expected to pick up again across the entire region after 18Z. Heavy rain and downburst with 50KT gusts are possible with these storms. The mountain TAF sites can expect periods of low ceilings and reduced visibility with these storms along with areas of terrain obscuration.

HYDROLOGY

Issued at 944 AM MDT Wed Sep 16 2026

HiRes guidance continues to suggest stratiform rain bring the dominant storm mode for the next 24-48 hours. 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 tomorrow. 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 through late tonight for UTZ022-028-029.