970
FXUS65 KGJT 171120
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
520 AM MDT Fri Jul 17 2026

.KEY MESSAGES...

- Expect terrain-based showers and thunderstorms each afternoon
  this week, favoring the San Juans, but spreading north by the
  weekend.

- Localized heavy rainfall will have the ability to produce
  flash flooding and debris flows in vulnerable terrain,
  including areas near and downstream of burn scars.

&&

.DISCUSSION...
Issued at 1055 PM MDT Thu Jul 16 2026

DAILY SHOWERS AND THUNDERSTORMS:

Persistent high pressure aloft keeps a plume of moisture over
much of the West through at least this weekend, potentially
beyond. Guidance keeps the most moisture rich part of this plume
(in terms of PWAT anomalies) to our west, but ensembles place
PWATs of 130- 200% of normal over our forecast area this week.
This moisture brings daily chances of showers and thunderstorms
in the afternoon and evening through next week.

Convection on Friday will look similar to what we saw today
(Thursday) as the pattern remains unchanged. Initiation will be
favored over the higher terrain before spreading over the
valleys as outflows develop. Lightning and heavy rain will be
the primary threats, with small hail and gusty outflow winds up
to 35-45 mph on the table as well.

While moisture is a relief for drought conditions, it also
creates a risk of flash flooding and debris flows, including
over area burns scars. The hydrology section below discusses
this risk in greater detail. These storms can develop quickly,
so be sure to monitor the forecast and have a way to receive
weather alerts, especially if you are visiting or reside below
terrain that is vulnerable to flash flooding, including
downstream of active fires.

COOLER TEMPERATURES:

Near-normal temperatures made a comeback on Thursday and remain
in the forecast into early next week. Current model data
suggests that we could see temperatures around five degrees
below normal move in around the middle of next week. &&

&&

.AVIATION /12Z TAFS THROUGH 12Z SATURDAY/...
Issued at 520 AM MDT Fri Jul 17 2026

Plenty of moisture is in place which will once again allow
convection to blossom by midday over the terrain with the flow
carrying these storms of the terrain to adjacent valleys through
the evening...possibly impacting TAF locations. Gusty outflow
winds and locally heavy rain will be the main concern with
storms. There is a low probability of MVFR occurring due to
visibility restrictions in the heavier showers otherwise VFR
prevails.

&&

.HYDROLOGY...
Issued at 1235 PM MDT Thu Jul 16 2026

An anomalous plume of moisture continues to rotate into Utah
and western Colorado this afternoon, with a slight uptick
compared to yesterday. The San Juans remain a bullseye in
precipitation forecasts this afternoon and again on Friday,
maintaining flash flood threats redeveloping each afternoon.
However, available moisture is higher moving west into Utah,
which leaves the potential for isolated storms to produce hourly
rainfall rate of 1-2 in. Therefore, areas of concern remain
unchanged from the previous forecast for this afternoon.

Storms over the last 24 to 48 hours have only helped prime
lower levels of the atmosphere and saturate the ground where
rain was observed. Several locations across southwest Colorado
reported over 0.5 inches of rain within 30 minutes during
yesterday`s convection; which is more than sufficient to create
issues in our steep, rocky terrain already susceptible to flash
flooding. This environment also triggers heightened awareness
over recent (or actively burning) fires, due to the burnt
ground`s inability of absorbing moisture under heavy rainfall.
As such, we continue to emphasize the potential for flash
flooding and debris flows in this regime.

As a reminder: Keep an eye on our forecasts through the end of
the week and stay tuned for updated hydro alerts if visiting or
if you reside below vulnerable terrain to flash flooding and/or
debris flows. Storms across the west develop quickly, leaving
little room for lead time in flashy terrain.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

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