020
FXUS65 KGJT 160537
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
1137 PM MDT Tue Sep 15 2026

.KEY MESSAGES...

- Flash flooding will be possible as potentially record moisture
  passes through western Colorado and eastern Utah.

- Flood Watch in effect for SE Utah and SW Colorado Wednesday
  through Thursday.

- While vulnerable locations like slot canyons and burn scars
  will be at the highest risk of flash flooding and debris
  flows, impacts could be observed at multiple locations across
  the region.

&&

.DISCUSSION...
Issued at 1004 PM MDT Tue Sep 15 2026

With moisture still plentiful and an afternoon sounding
bolstering the most CAPE we`ve seen in quite some time (nearly
2000 J/kg), today saw, and continues to see, heightened storm
activity. High rainfall rates have prompted numerous flash
floods and powerful storms have dropped severe winds and small
hail. As we progress through the overnight hours, a mixture of
stratiform rain showers and clusters of stronger convection are
expected to continue. While the wind and hail threat should
diminish with lessened instability, rain rates could continue to
be a concern and a few additional flash floods or debris flows
cannot be ruled out.

EXTREMELY MOIST WEDNESDAY AND THURSDAY:

Believe it or not, we will transition into an even wetter
environment over the next 48 hours as yet another surge of sub-
tropical moisture pushes into the Intermountain West through
the persistent southwesterly flow. Ensembles are keying in on
PWAT`s nearing 300% of normal, particularly focusing on the
southwestern corner of Colorado. At this magnitude of an
anomaly, PWAT`s are not just forecasted to break records, but to
crush them.

With that much moisture, it`s almost a certainty that cloud
cover will be widespread for the vast majority of the next 48
hours. This is the one factor dampening storm potential, and
CAM`s are responding by depicting a stratiform storm mode
dominating the region. While we often talk about stratiform
rainfall being less threatening to flash flooding concerns due
to weaker rainfall rates, the Wednesday/Thursday event isn`t
quite in the same boat. For one, the low-level environment and
soils will have both sufficiently saturated by this point thanks
to many portions of the region seeing 1+ inches of rainfall
over the past couple days. This will lead to efficient rainfall
and minimal absorption by said soils. We`ve already seen some
vulnerable locations produce flash flooding and debris flows
with weaker rainfall rates, an indication that there is little
room left for the land to take on more water. Secondly, just
because stratiform storms will dominate does not mean embedded
stronger cells cannot develop. Between upper-level jet support,
a pronounced shortwave passing through (roughly between 6 PM
local time Wednesday through 6 PM local time Thursday), and
enhanced PVA with the southward digging of the west coast low,
the dynamics are in place for a handful of strong updrafts and
especially wet rainfall rates. Even so, it is likely that we
will see less of the hail and wind threat over the next couple
days, and more of the hydrologic threats. Refer to the hydro
section below for more detailed information on what to expect.

FRIDAY AND BEYOND:

On Friday, the moisture pool driving this wet weather rapidly
diminishes. Though, given just how wet we are expected to peak
at, even with this decrease in moisture we are confident that
the majority of the region will still see above normal PWAT`s
through the weekend. With the low beginning its eastwards
movement though, and with little in the way of forcing, storm
activity should become less pronounced. On Friday, there looks
to still be enough moisture to keep storm coverage scattered.
By Sunday though, look for most shower and thunderstorm
development to be confined to the high terrain as convection
will be driven by orographics.

&&

.AVIATION /06Z TAFS THROUGH 06Z THURSDAY/...
Issued at 1137 PM MDT Tue Sep 15 2026

Unsettled conditions will persist over the next 24 hours with
periods of showers and thunderstorms impacting all the TAF
sites. Through sunrise much of this activity will be over the
northern TAF and KTEX is in line for another batch of storms
moving in from the Southwest. Gusty outflow winds and heavy
rainfall rates have a low probability of dropping flight
conditions to MVFR overnight. 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 along with areas of terrain obscuration.

&&

.HYDROLOGY...
Issued at 1004 PM MDT Tue Sep 15 2026

It`s a difficult forecast when the dominant storm type will be
stratiform rain, but soils have been so saturated over multiple
days of moderate to heavy rainfall. What will be more pertinent
to the event: lighter rain rates or the lack of absorption from
soils? In the end, the answer will likely vary across the
region. In this, as we approach this Wednesday through Thursday
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. This is, as usual, especially
important for vulnerable areas like slots canyons and burn
scars. But the sheer persistence of precipitation will mean even
less vulnerable areas are at risk of hydrologic complications.
Additionally, QPF for multiple forecast cycles has highlighted
an especially wet bullseye on the southern slopes of the San
Juans and into the Animas and San Juan River Basins where
48-hour totals are exceeding 2 inches and nearing 3 inches in
some locations. As a result, southern portions of the CWA are in
a Flood Watch for portions of the coming 48 hours. Stay aware
of road conditions, avoid locations known to be prone to flash
flooding, and report flooding or other weather impacts to local
law enforcement.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

CO...Flash Flood Watch until 3 AM MDT Wednesday for COZ002-003.
     Flood Watch from Wednesday afternoon through Thursday evening
     for COZ018-019-021>023.
UT...Flood Watch through late Wednesday night for UTZ022-028-029.

&&

$$

DISCUSSION...BW
AVIATION...TGJT
HYDROLOGY...BW