271
FXUS65 KGJT 231732
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
1132 AM MDT Tue Jul 23 2024

.KEY MESSAGES...

- Thunderstorms will be favored the next few afternoons to the
  San Juans and along the spine of the Continental Divide.

- Hot temperatures move in for Tuesday through Thursday with
  triple digit readings expanding over the lower desert valleys.

- A push of monsoonal moisture is expected late week, bringing
  increasing storm coverage. Some uncertainty remains over how
  long this moisture will linger over the area.

&&

.SHORT TERM /THROUGH WEDNESDAY/...
Issued at 229 AM MDT Tue Jul 23 2024

An anomalously dry airmass will remain in place the next few
days as the SubTropical High lingers over the western Great
Basin. Unfortunately the flow around this High is transporting
wildfire smoke out of the PacNW and N.Rockies region and
dropping into the Rockies. Hazy conditions and compromised air
quality is not likely to improve until this high pressure system
is bumped eastward later in the week. Back to the dry
conditions the 00Z sounding at GJT was sitting at 0.42 inches
which is in the 10th percentile for what should be close to the
peak PWAT for the year. This dry air will limit thunderstorm
chances the next few afternoons to the higher terrain...with the
San Juans favored and few adjacent southerly valleys as the
storm drift off the hills. There appears to be just enough
moisture lingering in the profile for moderate to heavy rainfall
bursts near our southern border...which if in the right
place...continues to cause some runoff issues. This threat
however remains highly localized. Otherwise temperatures remain
above normal with triple digit readings spreading across the
lower valleys. Grand Junction has seen the past 29 days at 90
degrees or above and this forecast keeps the string alive for at
least another week. We have a ways to go to match the number 1
spot of 52 days in a row of 90+ highs set back in 2008.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
Issued at 229 AM MDT Tue Jul 23 2024

A trough moving through the Pacific Northwest on Wednesday night
will begin to flatten and elongate the ridge of high pressure that
has been focused over the Great Basin the last several days. This
will result in the axis of high pressure stretching overhead from
SoCal/Southwest Arizona all the way into the northern Great Plains,
and will bring one more day of above normal temperatures to eastern
Utah and western Colorado. Look for highs to run 5-10 degrees above
normal, and for the lower desert valleys to see triple digit heat
once more. As the ridge continues to flatten and break down, a surge
of monsoonal moisture is forecast to make it into eastern Utah and
western Colorado beginning Thursday afternoon and continuing into
the weekend. This moisture is expected to be maximized on Friday,
with PWAT anomalies running 120-150% of normal across the area. At
the same time, a weak frontal boundary is expected to drop into
northern portions of the CWA, acting as a source of lift and a focus
for shower and thunderstorm development, in addition to the more
typically favored higher terrain. Shower and thunderstorm activity
will be at its most widespread on Friday, although Saturday will be
a close second, as above normal moisture sticks around and the
frontal boundary lingers over the higher terrain. Look for the most
widespread activity to shift eastward, favoring areas along the
Divide. With ample moisture in place, stronger storms will be
capable of producing heavy rainfall and the potential is there for a
flash flood threat in vulnerable areas. Gusty winds, hail, and
frequent lightning will also be threats.

By Sunday morning, broad troughing is forecast over much of the
western CONUS, with high pressure shunted to our south.
Unfortunately, this set up will also push the moisture plume east of
the Divide, resulting in a drying trend as we enter the coming
workweek. How quickly things dry out is still somewhat unclear, as
models are often far too quick to dry things out after a monsoonal
push. What can be said is that models are very keen on moving drier
air into the region by Monday, resulting in a downturn in activity.
Lingering pockets of surface based moisture will result in some
shower or storm activity across the higher terrain, but will be
isolated to widely scattered at best. With drier air working in,
look for the main threats with storms to be primarily gusty winds
and lightning, with small hail and brief heavy rain also possible.

Temperatures will start the long term running 5-10 degrees above
normal, but will drop to near normal values Friday through Sunday
thanks to increased moisture, cloud cover, and showers. A gradual
warming trend will kick in for Monday as conditions begin to dry
out.

&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 1129 AM MDT Tue Jul 23 2024

Smoke will continue to infiltrate the northerly flow aloft and
bring hazy conditions. There is some reduction in visibility
due to the smoke/haze at KGJT but no other reports at other TAF
sites as of yet. Isolated thunderstorms are possible over the
higher terrain today but models are indicating a downturn in
coverage. Did not include any mention of convection at TAF
sites. Widespread VFR will continue as will the hazy conditions.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

SHORT TERM...15
LONG TERM...BGB
AVIATION...TGR