349
FXUS65 KGJT 120611
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
1211 AM MDT Sun Oct 12 2025

.KEY MESSAGES...

- Scattered storms will develop ahead of a strong cold front
  expected to move through this evening and overnight, bringing
  continued threat of heavy rainfall and flash flooding as
  moisture from the remnants of Tropical System Priscilla
  remains in place.

- Excessive runoff from rainfall rates in excess of an inch per
  hour may result in flooding of slot canyons, normally dry
  washes, slickrock areas and urban areas. Recent burn scars and
  already saturated areas from recent abundant rainfall will be
  especially vulnerable to flash flooding.

- Smaller waterways may respond quickly to heavy rainfall leading
  to localized flash flooding. However, major rivers are not
  expected to exceed flood stages at this time.

- Isolated severe storms are possible today and tonight. Heavy
  rain and damaging winds are the primary threats with large
  hail as the secondary threat.

- Drier conditions expected Sunday behind the cold front with
  unsettled conditions returning Monday through the coming week.

&&

.SHORT TERM /THROUGH SUNDAY NIGHT/...
Issued at 355 PM MDT Sat Oct 11 2025

Much of the area has seen plentiful rainfall over the last 36
hours as moisture from the remnants of Tropical System Priscilla
continued to track over the region. SNOTEL sites were recording
upwards of 4 plus inches of rainfall in the San Juans with many
valley locations reporting 1 to 2 plus inches of rain. All of
this rainfall has been stratiform and the main plume that
remained in place this morning has now shifted east of the
Divide, making way for some clearing to our west across Utah and
portions of western Colorado. There is still plenty of low level
moisture as evident from our 18Z GJT sounding as well as dew
point temperatures in the 50s. This is resulting in quick
development of showers and storms, more scattered in coverage
but the intensity is less due to recent morning cloud cover and
moisture reducing the instability and lapse rates a bit. We are
still seeing around 200 J/kg of CAPE with CAPE expected to reach
up to 500 J/kg in some areas if enough surface heating can take
place. A cold front is just on our doorstep, currently located
in northwest Wyoming down through northwest Utah. This cold
front is currently timed to track across the area late this
evening, reaching northeast Utah by 10 pm and crossing through
northwest and west-central Colorado in the early morning hours
past midnight, reaching the Divide mountains by sunrise. The
hi-res CAMs have been consistent with the timing of the front
with a line of showers and storms accompanying the cold
front...so you could wake up in the middle of the night to some
lightning and rumbles of thunder as well as heavy rain. Some
storms could be strong this evening ahead of the front with
strong winds and hail possible in addition to heavy rain.

The main concern with the convective and thunderstorm potential
is that much of the area is already saturated by recent rainfall
that has well exceeded our usual monthly total in only a couple
of days. So any heavy rain rates on already saturated soils
could lead to flash flooding as it will not take much to
generate flooding given how much rain fell. Recent burn scars
will also need to be watched closely. A lot of the rain that
fell in the higher terrain is all flowing down into streams and
rivers so flows are a bit higher causing some flooding in some
areas, especially in southwest Colorado. Felt that the current
Flood Watch covered the ongoing threat well and left the current
expiration at 6 am MDT Sunday morning as the front and heavy
rain potential should be just about out of here by then once the
front moves east of the Divide.

Much drier air moves in behind the cold front as PWAT anomalies
drop significantly from 200 to 300+ percent of normal this
afternoon down to 40 to 80 percent of normal on average by
Sunday afternoon. So, Sunday afternoon will be an overall dry
day with little in the way of precipitation expected...giving us
at least 24 hours to dry out before the next round of moisture
arrives from the south on Monday. More details in the Long Term
on this next moisture push.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
Issued at 355 PM MDT Sat Oct 11 2025

On Monday a low pressure system moves southward along the West
Coast allowing for southerly flow to develop across our region.
That flow will start to tap into the deep moisture in AZ/NM and
advect it into our area. Therefore the chances for showers and
storms increases with the highest chances in and around the San
Juans. Given the moisture values (PWATs up to 250% of normal)
moderate to heavy rainfall will be possible with these showers.
The southern San Juan mountains and San Juan upper river basin
have received 2-4 inches the last 36 hours, so the soil is super
saturated there. As a result the response to rain will be
quick, which could lead to flooding. The moisture advection
continues into Tuesday as that main low pressure tracks over
central California and lifts over the Great Basin on Wednesday.
The associated cold front passes through the CWA on Wednesday
therefore precipitation should start to dissipate behind it.
With slightly cooler temperatures than what we are currently
experiencing snow levels should be lower, so more snow is
expected mainly above 11 kft. Snow levels could change based on
the track of the low, so stay tuned. Conditions look to stay
relatively quiet once the precipitation comes to an end late
Wednesday.

&&

.AVIATION /06Z TAFS THROUGH 06Z MONDAY/...
Issued at 1145 PM MDT Sat Oct 11 2025

A line of showers and thunderstorms associated with a cold
currently along a line KRWL-KHVE is moving northwest to
southeast across the region at about 30kts. These storms are
producing brief periods of MVFR to IFR ceilings and visibilities
below ILS breakpoints. Look for this system to push into the
northern and central Colorado mountains by 12Z where the front
will stall out and the showers will diminish through the
morning, ending by about 18Z. There is a slight chance for an
isolated shower or thunderstorm between 18Z and 00Z over the
higher terrain with skies clearing this afternoon and evening.


&&

.HYDROLOGY...
Issued at 355 PM MDT Sat Oct 11 2025

Tropical moisture will remain in place with scattered showers
and thunderstorms developing ahead of and along a cold front
moving through this evening and overnight. Any heavy rainfall
rates on already saturated soils from previous rainfall could
result in flash flooding across the region, especially for
southeast Utah and southwest Colorado where moisture was more
abundant. An increased risk of flash flooding will continue
through late tonight across the watch area.

Excessive rainfall may result in flooding of slot canyons,
normally dry washes, slickrock areas, recent burn scars, urban
areas, and other low-lying and flood-prone locations. Rockslides
and mudslides will also be possible in the mountains.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

CO...Flood Watch until 6 AM MDT Sunday for COZ001>003-006>014-
     017>023.
UT...Flood Watch until 6 AM MDT Sunday for UTZ022>025-027>029.

&&

$$

SHORT TERM...MDA
LONG TERM...KJS
AVIATION...DB
HYDROLOGY...TGJT