401
FXUS65 KGJT 132336
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
536 PM MDT Sat Jul 13 2024

.KEY MESSAGES...

- Near record heat continues through tomorrow, especially for
  the desert valleys of eastern Utah and the Grand Valley in
  Western Colorado. Heat Advisories remain in place.

- Showers and thunderstorms remain in the forecast over the
  higher terrain throughout the next 7 days, although the
  greatest coverage will occur tomorrow and Monday.

- Temperatures will begin to cool off somewhat midweek onward, although
  they will remain around 5 degrees above normal.

&&

.SHORT TERM /THROUGH SUNDAY NIGHT/...
Issued at 145 PM MDT Sat Jul 13 2024

Based on current satellite imagery, the center of the dome of high
pressure is located over eastern Utah, somewhere south of Moab.
Models have a good grip on this, although they are struggling a
little with the ongoing afternoon convection. The moisture present
is fairly modest, with this morning`s 12z GJT sounding coming in
with a PWAT of 0.59 inches, and dew points at this hour in the mid
to upper 30s. But, with strong differential daytime heating and a
modest 500 J/kg of CAPE, it`s enough to fire showers and
thunderstorms off the higher terrain across the region. Dry surface
layers, as indicated by this morning`s Inverted-V sounding, with
keep gusty outflow winds as the main threat, followed by frequent
lightning and small hail. A brief heavy shower is possible. Thus far
these showers and storms have remained anchored to the terrain, and
are slowly drifting in a clockwise direction around the above-
mentioned center of the high. This will continue through the
afternoon before things die off with loss of heating after sunset.
With the high nearly directly overhead today, look for some of the
hottest temperatures of the week, with the exception being areas
that see clouds and showers.

The center of the high is expected to continue drifting east through
the evening and into the overnight, pulling the moisture plume on
its western edge along with it. This plume will set up shop over
eastern Utah and western Colorado beginning late tonight, and is
expected to remain in place through the next few days. Models remain
consistent on PWATs increasing to 100-150% of normal, although much
of this moisture will remain aloft, as it takes time to mix out the
dry surface layers. This means there will be an increase in shower
and storm coverage tomorrow afternoon, especially over the terrain,
but the main threats will remain gusty winds and lightning, with
lesser chances of small hail and brief heavy rain. The expansion in
cloud and storm coverage tomorrow afternoon will bring high
temperatures down a few degrees compared to today, but with the
lower desert valleys still expected to see highs of 100-110 degrees,
the Heat Advisory remains in place through 9PM tomorrow evening.
Additionally, the increasing moisture will keep nighttime lows
tonight and tomorrow night even more mild than we`ve seen in
previous days, with the desert valleys again see the worst of it
with forecast lows in the mid 70s. This means minimal relief from
the heat if you don`t have some form of cooling available to you.
Remember to stay hydrated and avoid doing outdoor activities during
the heat of the day if possible. Relief is in sight as we move into
the coming work week.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
Issued at 145 PM MDT Sat Jul 13 2024

The high pressure ridge will be situated slightly east of the area
by Monday, allowing for sub-tropical moisture to circulate around
the high as PWAT anomalies rise up towards 100 to 150 percent of
normal. Monday and Tuesday appear to be the more active days in
terms of shower and thunderstorm activity with more scattered to
widespread coverage. Additionally, shortwaves will move through the
flow, causing the high pressure center to retrograde a bit back to
the south and west heading into Tuesday. These shortwaves may also
result in stronger storms with gusty outflow winds and small hail
the primary concerns. The moisture increase is enough to increase
cloud cover and cool things down a tad (by about 5 degrees compared
to this weekend), but not quite robust enough to warrant widespread
heavy rain threat. Some locally moderate to heavy rain is still
possible with some storms but gusty outflows seem like the better
bet with drier air already trying to sneak back in by Tuesday
afternoon as the high retrogrades westward. Temperatures will still
be hot though despite the moisture and storm increase, staying 5
degrees above normal on average compared to almost 10 above normal
currently.

By Wednesday, the high pressure ridge axis will be over the Great
Basin to our west, with enough lingering moisture to warrant daily
afternoon showers and storms over the high terrain. A bit of an
increase may occur late next week as more shortwaves round the top
of the high through the Northern Rockies and down the Front Range,
acting on leftover moisture to warrant better storm potential. The
high however remains to our west so not seeing any new moisture
advection, just recycled moisture under the high. Temperatures stay
around 5 degrees above normal through the end of the week for much
of the area with near normal temps for the higher terrain and
southwest Colorado where better chance for storms remains.

&&

.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 532 PM MDT Sat Jul 13 2024

Storms fired this afternoon but are staying away from TAF
sites, except KTEX, as they fired off the terrain. Plenty of
outflow boundaries are moving across the region so a quick popup
over the next hour or two is possible. Gusts of 35 mph have
been noted from the stronger cells so that will remain a concern
this evening. Calm conditions expected overnight with some high
broken clouds becoming few to SKC by daybreak. Similar
conditions expected again tomorow.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

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