067
FXUS65 KGJT 111839
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
1239 PM MDT Tue Aug 11 2026

.KEY MESSAGES...

- Terrain based showers and thunderstorms will continue Tuesday.
  Gusty outflow winds, lightning and dry lightning will remain
  threats.

- Moisture increases through the week with an uptick in storm
  coverage and intensity expected Wednesday onwards.

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

- Temperatures cool down now through the weekend.

&&

.DISCUSSION...
Issued at 1233 PM MDT Tue Aug 11 2026

Today, near-surface conditions are still on the drier side in
spite of moisture creeping into the region. Today`s 18Z sounding
indicates an environment similar to this time yesterday, albeit
with less instability. Like yesterday, storm development is
expected, though virga showers will likely dominate with sparse
areas of measurable rain (primarily over the high terrain) and
little chance for wetting rain. On Wednesday, the broad high
centered overhead skirts eastwards, shifting upper-level flow
from westerly to southerly/southwesterly. In this shift, mild
moisture from the Gulf and the Baja Peninsula rises northwards
through the Desert Southwest towards our region. More notably
though is the potent moisture plume to our west, which is
currently rising into the Great Basin. The shifting high will
pull that moisture eastwards over our CWA, which should be the
final push needed to saturate our low-levels and bring about
another round of widespread showers and thunderstorms.

The strongest portions of the moisture plume slide north of us
through Wyoming, but ensemble PWAT`s are forecasted at 150-180
percent of normal across portions of the CWA nonetheless. This
should be sufficient to prompt widespread rainfall Wednesday
onwards, including some stronger cells capable of producing
localized heavy rainfall. The threat for flash flooding and
debris flows appears to be maximized on Thursday, but a marginal
threat remains in place Wednesday, Friday, and possibly through
the weekend as well. The manifestation of this threat will
depend on when and where we see substantial lift and/or
instability. The lift part of that equation is where uncertainty
is greatest. Deterministic models are hinting at some shortwave
features transiting the ridge through the mid- and late-week
period, though there is very little agreement on when these will
occur, if they manifest at all. Models are better-aligned in
regards to instability though. Per yesterday`s 00Z sounding,
mixed-layer CAPE neared 1000 J/kg, and deterministic models are
signaling that this sort of instability, if not stronger, will
continue through the work week. This will also mean potential
for sub-severe hail and winds. As the low-level atmosphere
continues to moisten up today and Wednesday, gusty winds will be
favored.

In spite of the model agreement, some doubt in the development
of strong instability is being cast due to the anticipated
scattered cloud cover during mornings. This is often one of the
biggest caveats we must consider during monsoonal pushes, and it
will be a key consideration over the coming days. Should
morning cloud cover be ample, look for thunderstorms to
generally be short-lived and more stratiform-type storms to
quickly develop. Conversely, if clearer morning skies present
themselves, stronger discrete storms will be favored. At this
time, it is too difficult to speculate which mode will come to
fruition on which days, so stay up-to-date with future forecast
updates for additional information. Either way, wet weather is
on its way.

&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 1155 AM MDT Tue Aug 11 2026

Showers and thunderstorms will form on the terrain this
afternoon. Breakpoint conditions will likely be only temporary
at the terminals, as these showers decay over the valleys. Gusty
outflow winds will be the primary threat to aviators during
these showers. VFR conditions will return this evening. Some
high based ceilings will begin to develop ahead of a bigger push
of monsoonal flow late tonight and early Wednesday. Ceilings
will likely remain well above breakpoint through the overnight
hours, with light winds.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

CO...None.
UT...None.

&&

$$

DISCUSSION...BW
AVIATION...TGJT