488
FXUS65 KGJT 270703
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
103 AM MDT Sun Sep 27 2026

.KEY MESSAGES...

- Warmer and drier conditions continue Sunday.

- Another push of moisture will arrive by Monday, bringing
  widespread moderate to heavy precipitation through midweek.

- Flood Watch in effect from 6am Monday through 6am Wednesday
  for southern portions of the forecast area.

- Drier conditions return late week.

&&

.UPDATE...
Issued at 1246 AM MDT Sun Sep 27 2026

Issued a Flood Watch valid Monday morning through Wednesday
morning for southern portions of the forecast area. Guidance
continues to highlight remnant moisture from tropical systems
interacting with several stronger disturbances. This will
result in numerous showers and embedded thunderstorms through
that period, some of which could produce heavy rainfall. This
will occur over already saturated soils and burn scars where
mud/debris flows have already occurred over the summer. Flooding
will be possible over burn scars, at low- water crossings, and
along creeks, streams, washes, arroyos and other flood-prone
locations. Creeks and streams may rise out of their banks.
Unpaved roads could become muddy and impassable.

&&

.DISCUSSION...
Issued at 1029 PM MDT Sat Sep 26 2026

A pattern shift begins to develop on Sunday as an open trough
digging out of the PACNW begins to scoop tropical moisture into
the southwesterly flow over the Southwest. Temperatures will
remain near normal Sunday afternoon, but skies will cloud over
as upper level moisture fills in. A few isolated showers could
develop on the mountains Sunday afternoon, but measurable rain
will remain in short supply as we wait on the deeper tropical
moisture to develop Sunday night. PWAT values surge in excess of
200 percent of normal Sunday night for the Four Corners and much
of southwest CO. With the jet overhead providing some lift, we
should see rain develop across much of the region by daybreak
Monday. This will begin a wet 48 hours for our CWA as the
remnant moisture from multiple tropical storms gets entrained
into the southwesterly jet streak aloft.

With this jet overhead Monday, forcing and moisture will work in
concert to produce training showers over much of southeast UT
and southwest CO. The best rainfall rates appear to remain
confined to areas south and east of the Colorado Basin for
eastern UT and south of the Uncompahgre Plateau/San Juans. Areas
to the north will get some wetting rain, but flash flood
concerns trend better to the south. The upper low begins to lift
out of the region on Tuesday, taking much of the moisture with
it. However, convection around the low will likely continue the
threat for flash flooding on rain soaked soils.

High pressure returns to the region Wednesday and begins to dry
things out in the atmosphere, with temperatures returning back
towards normal values Thursday and Friday. Models begin to hint
at a clipper system dragging through northern CO next weekend.
This could produce some cooler conditions for the northern
mountains, depending on the evolution of this disturbance.

&&

.AVIATION /06Z TAFS THROUGH 06Z MONDAY/...
Issued at 1136 PM MDT Sat Sep 26 2026

A few clouds will drift overhead tonight but not pose any
aviation concerns. Tomorrow, clouds will be on the increase in
the afternoon ahead of the next system. A few afternoon gusts
will be possible, very similar to Saturday. VFR conditions will
remain in place for the next 24 hours.

&&

.HYDROLOGY...
Issued at 233 PM MDT Fri Sep 25 2026

In the wake of today`s precipitation, our attention will turn
to the Eastern Pacific. Tropical moisture is anticipated to
spread across the Desert Southwest early next week, drawing
moisture from a pair of Hurricanes; Odalys and Polo. The
forecast becomes increasingly complex due to a closed low
currently forecast to drive across the Southwest CONUS as
Hurricane Polo approaches the Baja California Peninsula. Strong
southerly winds ahead of the low are expected to pull tropical
moisture towards eastern Utah and western Colorado as early as
Monday morning. The challenge and uncertainty in our
precipitation forecast increase as the week progresses and the
low traverses our southern States. Excessive rainfall is most
probable over AZ and NM, attm, but the northerly extent poses a
threat to our southern San Juan river basins. Current forecasts
suggests 1 to 3 inches of rain over Monday morning through
Wednesday. At face value, rivers and tributaries will see a bump
up due to said moisture. However, localized heavier amounts
could result in minor flooding across the southern San Juan
foothills and communities further downstream.

Rivers have responded rapidly to recent rainfall due to
saturated soils and increased runoff potential. Thus, prolonged
periods of additional rainfall over these regions would trigger
a similar response. The current precipitation forecast suggests
larger peaks in several creeks and rivers than what has been
observed over the previous 7 days. However, high end
probabilistic rainfall amounts (i.e. above 90th percentile) may
lead to rivers exceeding action stage to minor flooding. Most
probable basins to see significant rises include; the Rio
Blanco, San Juan, Piedra, Los Pinos/Vallecito Creek, and the
Animas River Basins.

Convective storms and periods of heavy rainfall fed from said
tropical moisture could result in localized flooding impacts
across the CWA, however, confidence decreases rapidly north of
the San Juans. Confidence has increased enough for a Flood Watch
to be issued for southern portions of the forecast area valid
from 6am Monday through 6am Wednesday. Even so, please continue
to monitor the latest forecasts especially for those who reside
and/or plan to recreate in the Watch areas.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

CO...Flood Watch from Monday morning through late Tuesday night for
     COZ017>023.
UT...Flood Watch from Monday morning through late Tuesday night for
     UTZ022-028-029.

&&

$$

UPDATE...TGR
DISCUSSION...LTB/TGJT
AVIATION...TGJT
HYDROLOGY...ERW