533
FXUS65 KGJT 122114
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
314 PM MDT Fri Jul 12 2024

.KEY MESSAGES...

- Near-record daytime temperatures are expected today and
  Saturday especially in the lower valleys.

- Afternoon showers and thunderstorms will develop over higher
  terrain each day throughout the seven-day forecast with an
  increase in coverage expected early next week.

- Temperatures remain elevated beyond the weekend, but some
  relief is expected from cloud cover and shower activity as
  monsoonal moisture is forecast to return early next week.

&&

.SHORT TERM /THROUGH SATURDAY NIGHT/...
Issued at 314 PM MDT Fri Jul 12 2024

High pressure continues to sit to our west, directing a
northerly flow across the area. This is allowing the heat dome
to persist, with warm air advection to continue through the
weekend as the high pressure shifts directly overhead by
Saturday. Near record high temperatures are possible across the
area with triple digit heat across eastern Utah and west-central
Colorado valleys, in fact we are already there this afternoon.
The Heat Advisory remains in effect through Saturday and made
no changes to the coverage area or timing due to the
uncertainty of sub-tropical moisture return on Sunday and what
kind of impact increased clouds and storm activity will have on
the high temperatures for Sunday. This is something for later
shifts to re-evaluate. In this heat, make sure to limit your
exposure and stay hydrated.

Storms continued to develop again across the southern mountains
like yesterday, except a little bit further west across the
Abajos and La Sals. The HRRR seemed to have a better handle on
the timing and coverage of storms so nudged the PoP fields
towards the HRRR as well as hi-res WRF to better reflect these
trends in the forecast. Storms were hot to begin with on radar
but have since cooled down, but gusty outflow winds of 40 to 50
mph and lightning appear to be the primary concerns. The air
mass is very dry as evidenced by our 12Z GJT inverted V sounding
and relative humidity in the single digits to teens in the
lower valleys. These storms also have a tendency to drift into
the adjacent southern valleys but are collapsing as they do, so
again, gusty outflow winds will be common. Storms appear to be
driven by daytime heating, steep lapse rates upwards of 9C/km,
quite a bit of DCAPE and a little bit of shear, so small hail
is also possible. Storm activity should die down by sunset with
a similar story expected for Saturday with highs a bit hotter
than today and similar storm coverage over the high terrain with
high pressure directly overhead.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
Issued at 314 PM MDT Fri Jul 12 2024

By Sunday the high pressure that has been bringing all the heat
will be centered roughly over the Four Corners. This means
Sunday is likely to be yet another scorcher, especially for the
desert valleys where highs in the low 100s are once again
forecast. That said, by Sunday we are also expected to tap into
a plume of monsoonal moisture rotating around the high, with
PWATs forecast to climb to 100-150% of normal. This will lead to
increased storm coverage over the higher terrain, and an
increase of clouds overall, which may put a slight damper on
temperatures, but only by a few degrees compared to the days
previous. In addition, the prolonged period of hot and dry
weather prior to this monsoonal push means surface levels will
be extremely dry and will take some time to moisten. Therefore,
the main threats with any storms will be gusty outflow winds and
lightning, with the potential for some small hail or a very
brief downpour. A trough dropping through the Northern Plains
Monday into Tuesday will nudge the high back westward somewhat,
cutting us off from the moisture plume once more. The moisture
that did advect in on Sunday and Monday will stick around for a
bit, being recycled each afternoon and leading to daily showers
and thunderstorms favoring the terrain. This increased storm
coverage should continue to nudge temperatures down a few
degrees through the week. Highs on Sunday and Monday will run
around 10 degrees above normal, dropping to around 5 degrees
above normal by mid to late week.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 1118 AM MDT Fri Jul 12 2024

Under high pressure, look for generally clear skies this
afternoon and evening. A few storms are possible in and around
the San Juans, so have included VCTS for KTEX, KDRO, and KGUC.
Winds will be northerly and gust up to around 20 knots this
afternoon, before dropping and once again becoming light and
terrain driven. VFR conditions will prevail. Main threats with
any passing shower or storm will be gusty outflow winds and
lightning. Construction near the runway at KGJT has led to
periods of reduced visibility, so have included a tempo group to
account for this.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

CO...Heat Advisory until 9 PM MDT Saturday for COZ006.
UT...Heat Advisory until 9 PM MDT Saturday for UTZ024-027-029.

&&

$$

SHORT TERM...MDA
LONG TERM...BGB
AVIATION...TGJT