236
FXUS65 KGJT 122319
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
519 PM MDT Wed Aug 12 2026

.KEY MESSAGES...

- Moisture begins to increase today, with peak coverage expected
  Thursday.

- Localized heavy rainfall may prompt flash flooding and debris
  flows, especially around burns scars.

- Temperatures begin a cooling trend through the end of the work
  week, into the weekend.

&&

.UPDATE...
Issued at 1152 AM MDT Wed Aug 12 2026

A Flood Watch has been issued for forecast zones that encompass
the northwestern and southwestern San Juans until midnight.
Localized heavy rainfall may prompt flash flooding and debris
flows, especially around recent burn scars. Continue to be
weather aware and have multiple ways to receive watches and
warnings.

&&

.DISCUSSION...
Issued at 1025 AM MDT Wed Aug 12 2026

PRECIPITATION CHANCES THROUGH THE END OF THE WEEK:

The current synoptic level pattern is characterized by a high
pressure dome to our east, with troughing dominating the West Coast.
This will allow flow aloft over the Desert Southwest and Southern
Great Basin to transition to a more southerly-southwesterly regime.
Because of the clockwise circulation associated with high pressure
systems, this a prime setup for moisture advection. Recent sounding
profiles have been depicting consistent long, skinny CAPE profiles
which are indicative of favorable precipitation rates. Today,
saturation down to the surface is expected, with widespread showers
and thunderstorms in the afternoon, and wetting rains across the
higher elevations. This will lead to an increased threat for flash
flooding and burn scar debris flows today and Thursday.

By Thursday, shower and storm coverage is expected to peak. Hence,
chances for heavy rains, flash flooding, and debris flows also peaks
then. During these monsoonal patterns, some uncertainties can
present themselves when it comes to the forecast...

1. Cloud Cover

With these setups, morning cloud cover frequently lingers, much like
we`ve seen over the past few days, and will serve as a primary
driver for afternoon storm evolution. Robust daytime heating will
support more convective thunderstorm development. Conversely,
persistent cloud cover will limit instability, favoring a shift
toward broader stratiform showers. Lingering cloudiness will also
delay convective initiation, pushing storm development deeper into
the afternoon. Therefore, a lot can be dependent on how cloud cover
pans out for the day.

2. Lift

Storms will likely initialize along the higher terrain over the next
few days, which is typical for our CWA. However, subtle shortwaves
rotating around the edge of the upper level high could supply
additional mid-level lift. Lower confidence remains regarding the
precise timing and impacts of these impulses and lingering outflow
boundaries, creating uncertainty in convective coverage and
evolution once storms track off the ridges.

With all that being said, confidence is high that we`re moving into
a wetter period for the latter half of the week and even into the
weekend.

QUICK NOTE ON TEMPERATURES:

Temperatures begin to cool a few degrees each day as showers,
storms, and cloud cover begin to prevail. By Friday, daytime highs
will be below normal, a welcome relief from the previous stretch of
hot temperatures.

&&

.AVIATION /00Z TAFS THROUGH 00Z THURSDAY/...
Issued at 517 PM MDT Wed Aug 12 2026

Widespread showers and thunderstorms will continue to move from
south to north across the area through the next 12 hours. These
storms are capable of producing heavy rain, gusty winds, and
frequent lightning. Should one of these storms pass over a
terminal, conditions could drop to MVFR/IFR for a brief period
of time. Activity should begin to taper off after 06z this
evening, but could linger as late as 12z tomorrow morning. A
break in activity is expected before afternoon storms blossom
again after 18z. Outside of the influence of storms, winds will
be generally and terrain driven during the overnight period,
becoming westerly and gusting to around 20 knots in the
afternoon. VFR conditions will prevail.

&&

.HYDROLOGY...
Issued at 1152 AM MDT Wed Aug 12 2026

Moisture chances become more widespread today and peak in
coverage by Thursday. Model guidance suggests heavy rainfall
from thunderstorms and/or training storms is possible this
afternoon and into the late evening hours. With that being
said, a Flood Watch has been issued today for forecast zones
that include the northwestern and southwestern San Juans. This
also includes recent burn scars and steep mountain corridors in
that area. This Flood Watch goes until midnight tonight.
Continue to stay weather aware and have multiple ways to receive
watches and warnings.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

CO...Flood Watch until midnight MDT tonight for COZ018-019.
UT...None.

&&

$$

UPDATE...
DISCUSSION...BS
AVIATION...TGJT
HYDROLOGY...BS