169
FXUS65 KGJT 170539
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
1139 PM MDT Wed Sep 16 2026

.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.

&&

$$

DISCUSSION...MDA/TGJT
AVIATION...TGJT
HYDROLOGY...BS