289
FXUS65 KGJT 020540
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
1140 PM MDT Tue Jul 1 2025

.KEY MESSAGES...

- Increasing moisture will keep afternoon terrain based showers
  and storms in the forecast again Wednesday with some localized
  flooding concerns emerging.

- Widespread showers and thunderstorms are expected Thursday,
  with more concern for heavy rain and flooding issues.

- Temperatures will turn down through Friday, then increase
  again this weekend and beyond.

&&

.SHORT TERM /THROUGH WEDNESDAY NIGHT/...
Issued at 400 PM MDT Tue Jul 1 2025

A generous infusion of extra-tropical moisture turned up on the
mid day sounding here at Grand Junction, with PWAT`s increasing
by nearly 50 percent since Monday evening. This produced a
generous complex of thunderstorms on the San Juans today, most
of which have drifted southward and decayed into some light rain
on the terrain. A few gusty storms continue to radiate across
Dolores, Montezuma, and La Plata counties in the outflow
boundary. Elsewhere, scattered convection on the Tavaputs,
Bookcliffs, and Central Mountains is taking advantage of some
Pacific moisture pushing into the Great Basin. These storms have
been a little starved, as this supply of moisture is much more
anemic than that previously mentioned.

Tonight, showers will continue towards sunset, especially on terrain
that hasn`t been worked over yet this afternoon. These showers will
remain capable of producing some 40 to 50 mph outflows upon
collapse. The light upper level winds will keep activity mostly
anchored to the terrain. The digging trough along the West Coast
will work in concert with the amplifying ridge over the Plains on
Wednesday to send additional tropical moisture northward in the
meridional flow pattern.(For those wondering: this is not monsoonal)
This will lead to another active day on our terrain. PWAT`s reach
nearly 180 percent of normal by Wednesday evening. We will likely
tap into lighter moisture around 150 percent of normal during
afternoon instability. This should be good enough for another day of
rich convection. This will also put the brakes on the hot and dry
pattern for a minute, which we get into down below. Some of the
stronger moisture sets up across our eastern Utah zones, as well as
just across the state line. Slow storm movements and generous
moisture could produce some isolated flooding concerns Wednesday
afternoon. Models are keen to keeping some nocturnal activity going
into Thursday morning along the state line too. This will
potentially have an impact on storm initiation Thursday, but that
can wait for subsequent forecast packages.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
Issued at 400 PM MDT Tue Jul 1 2025

The closed low which is presently sitting off the west coast looks
to become an open wave on Thursday as it transits through the Great
Basin. Ensembles are confident that a pocket of highly anomalous
PWAT`s (upwards of 210% of normal in some locations) will be
embedded in the southwesterly flow on the front edge of the trough.
This positions the center of the pocket near northeastern Utah with
the entirety of our CWA benefiting from an uptick in moisture. As a
result, confidence is high in a widespread precipitation event on
Thursday. The NBM currently sits at 65-85% probability of
precipitation for the vast majority of the region, which is actually
a slight increase from guidance 24 hours ago. What may limit the
intensity of these storms will be the likely persistence of morning
cloud cover. Should we lose out on some instability from this, we
may be looking at more of a stratiform setup with more isolated
embedded storms being possible. High-resolution model guidance is
still limited, but as more data becomes available, we`ll begin to
better gauge how this wet event will unfold.

Models quickly diverge over the following days. While upper-level
flow is fairly well agreed upon between models on the 4th of July,
moisture content widely varies, with cluster analysis split evenly
between above- and below-normal QPF. Whatever moisture does persist
will be mostly confined to the northeastern portions of our CWA near
the Park Range. However, any amount of lingering moisture on the
backside of the departing trough may support scattered convection,
particularly along the high terrain, should orographics be
favorable. It is apparent that drier conditions resume heading into
the weekend, but consistency among models regarding the upper-level
flow appears to fall off greatly by this point.

&&

.AVIATION /06Z TAFS THROUGH 06Z THURSDAY/...
Issued at 1137 PM MDT Tue Jul 1 2025

Showers and mid level scattered to broken clouds are lingering
over the region this evening. The greatest impact will be gusty
outflow winds over the next 6 hours as activity gradually
diminishes. A few hours of quiet conditions can be expected
between 09z and 15z before showers and thunderstorms start to
develop over the higher terrain once again. Activity in the
afternoon will be more widespread, with increasing chances of
brief heavy rain in addition to gusty outflow winds and
lightning. Outside of this activity, winds will follow typical
terrain driven patterns. VFR conditions are expected to prevail,
although brief drops to MVFR conditions will be possible under
those brief heavy downpours.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

SHORT TERM...LTB
LONG TERM...BW
AVIATION...TGJT