013
FXUS65 KGJT 291803
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
1203 PM MDT Tue Sep 29 2026

.KEY MESSAGES...

- Scattered to widespread precipitation showers and storms
  continue.

- Increased flooding concerns for rain-soaked terrain,
  especially within and adjacent to the southern San Juans.

- A Flood Watch is in effect for southeast Utah and southwest
  Colorado through 6AM Wednesday.

&&

.DISCUSSION...
Issued at 958 PM MDT Mon Sep 28 2026

Dry slotting is beginning to intrude on the Four Corners at
this hour. This is acting to curb precipitation some across the
region. Light rain is still reaching the surface at many surface
observation sites. Some stronger rainfall is still coming down
across the San Juans. This is still an area of concern for
rising river levels, as highlighted in the hydrological
discussion below. Lower rain rates have kept flash flooding off
the table, but some basins could continue to rise due to the
persistent nature of the rainfall. Some areas have already seen
in excess of an inch of rainfall.

On Tuesday a pinched off low will drop out of the Great Basin
moving south of the Four Corners. This continues to pull dry air
in behind it which is expected to suppress some of our rainfall
in the northern half of the CWA on Tuesday. However, down south
rich moisture wrapped into the low will continue to add to the
flash flooding concern. Hi res models are keeping the stronger
convection south of the Four Corners on Tuesday, so rainfall
rates could take a hit downward.

The low lifts out of the Rockies onto the Plains Wednesday, but
a strong wraparound moisture plume is expected to produce
another surge of rainfall for southern CO through the afternoon.
Some colder air wrapped into the low looks to produce some
accumulating snow on the San Juans and up the spine of the
Divide Wednesday. Snow levels remain above pass level and much
of it will melt out in the warmer afternoon temperatures. This
should be the final gasp of the tropical moisture, as rainfall
tapers to a close by Thursday morning. High pressure begins to
build into the region on Thursday. Temperatures return to near
normal then begin to climb through the weekend back into the 80s
for the desert valleys and into the 60s for the mountains.
Models are playing with some showers cropping up on the
mountains Sunday and Monday, but that remains a very tentative
forecast at this point.

&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 1140 AM MDT Tue Sep 29 2026

Abundant moisture will lead to continued cloud cover and
scattered showers over the region this afternoon. Showers will
become widespread this evening south of I-70 with lesser
coverage over northern sites. Terrain obscuration will also be
widespread leading to areas of ILS to MVFR visibility in
adjacent valleys and associated TAF sites. Lower clouds
lingering behind the moisture could also lead to MVFR/IFR
conditions as stratus and/or fog develops.

&&

.HYDROLOGY...
Issued at 153 PM MDT Mon Sep 28 2026

The bulk of tropical moisture will be streaming across eastern
Utah and western Colorado today. Integrated water vapor
transport (IVT) maximizes this evening across the San Juans, so
anticipate precipitation amounts to wane as our moisture fetch
declines, too. River responses will be highly dependent on
precipitation totals, and peak flows will lag behind periods of
moderate rainfall. Forecast guidance shows peak arrival times
between midnight tonight to Tuesday morning, depending on river
segments and proximity to the watershed`s headwaters.

The Navajo River, Rio Blanco and San Juan River are forecast to
inch towards bankfull conditions and near action stage by early
Tuesday morning, with 2 to 2.5" of precipitation expected in
their upper basins. However, if locally higher amounts are
observed (i.e. exceeding the 90th percentile forecasts of 4.5 to
5.5 inches) then minor flooding is possible. Elsewhere, rivers
and creeks will also see a notable rise, but probabilities of
exceeding flood stage are lower. Nonetheless, a significant rise
in several streams, rivers and creeks is expected in response
to today`s tropical surge, and minor flood poses a threat,
namely across our southern counties.

The northern extent of moisture maintains some ambiguity as the
systems merge over the next 48 hours. However, after a brief
lull on Tuesday, wrap around moisture on the northern periphery
of the low could support another wave of precipitation across
the southern half of the CWA on Wednesday. As a result, river
forecasts reveal a secondary peak Wednesday evening, albeit,
less than its predecessor.

A Flood Watch remains in effect across southeast Utah and
southwest Colorado, where the higher precipitation totals are
favored. However, keep an eye on evolving conditions and
conditions upstream. Flooding continues to be a concern,
especially with rivers rising overnight.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

CO...Flood Watch through late tonight for COZ017-020>022.
UT...Flood Watch through late tonight for UTZ022-028-029.

&&

$$

DISCUSSION...TGJT
AVIATION...TGJT
HYDROLOGY...ERW