636
FXUS65 KGJT 181132
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
532 AM MDT Thu Jul 18 2024

.KEY MESSAGES...

- Temperatures are expected to remain a few degrees above normal
  with daily thunderstorm chances through the remainder of the
  week with a slight drying trend possible over the weekend.

- Threats from thunderstorms will mainly be from gusty outflow
  winds though a few storms will be capable of producing small
  hail and moderate to heavy rainfall rates. Overall flooding
  threats remain low.

- The combination of high based storms, gusty outflow winds and
  lightning will keep also keep a threat of new wildfire starts
  in the picture.

&&

.SHORT TERM /THROUGH FRIDAY/...
Issued at 342 AM MDT Thu Jul 18 2024

High pressure continues to remain to our west with moisture
trapped underneath the high, allowing for daily afternoon
convection over the high terrain. A bit drier air worked
underneath this high from the north yesterday, resulting in a
noticeable downturn in convective activity. The best moisture
remains across the Four Corners where some isolated showers are
still ongoing early this morning in southwest Colorado and
southeast Utah. Moisture will recirculate around this high with
a slight bump up in PWAT levels across the south, for a bit
more coverage of storms favoring the southern mountains and less
up north. Expect more of the same today as yesterday with gusty
outflow winds and lightning being the primary threats with
storms. Storms may have a tough time sustaining themselves in
the lower valleys due to dry low level air and a bit of CIN
present. Storms may have a better chance of lasting and
producing wetting rain in the southern valleys where the best
moisture resides but anticipate any wetting rain to be fairly
localized. Some hi res guidance is indicating some isolated
showers lasting through the overnight which cannot rule out as
this has happened last night and some embedded wiggles in the
flow remain.

By Friday, a shortwave disturbance will drop out of the north
down the Front Range and in addition to PWAT bumping up to near
150 percent of normal, should result in better coverage of
showers and thunderstorms. Storms should develop over the high
terrain initially and have better chance to impact some lower
elevations late in the day with the disturbance moving through.
The PWAT increase is not enough for widespread wetting rain but
some stronger storms could produce locally moderate to heavy
rain at times. The main threats from storms though continue to
be gusty outflow winds of 40 to 50 mph, lightning and possibly
some small hail given the inverted V soundings.

Temperatures through this period look to remain near normal,
with slightly above normal in the lower valleys and slightly
cooler than normal in the higher elevations given better chance
of increased clouds and storms.

&&

.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
Issued at 342 AM MDT Thu Jul 18 2024

The models continue to struggle to handle the high pressure to
the south that has dominated the weather pattern over eastern
Utah and Western Colorado for the last week or two and in
general struggle with the latitudes south of the 45th parallel
likely due to the weak flow through all levels and lack of upper
level dynamics. Run-to-run consistency is low and the ensembles
show fairly broad dispersion in solutions even in the near
term. That being said, the synoptic pattern remains dominated by
the Gulf of Alaska and Hudson Bay lows with strong ridging in
between in the Intermountain West, though ridge axis placement
varies between models and runs. Subtropical moisture caught up
in the flow around the high, along with residual moisture across
the region will continue to feed orographic showers and
thunderstorms driven by diurnal heating each afternoon lingering
into the evening and overnight periods. The lack of steering
flow creates a threat for localized flash flooding with these
slow moving storms in areas prone to flash floods like slot
canyons. Always take notice of your surroundings and the local
weather when you are out in these areas. With the inverted V
soundings, strong outflow winds with gusts of 40 to 50 mph are
likely with these storms as well as a threat of lightning and
small hail.

Clouds building up each afternoon along with showers will limit
diurnal heating keeping the daily high temperatures near normal
to about five degrees above normal for mid to late July. Skies
will clear out overnight allowing temperatures to fall to near
normal to about five degrees below normal by morning. Little
change in the pattern is likely for the foreseeable future.

&&

.AVIATION /12Z TAFS THROUGH 12Z FRIDAY/...
Issued at 532 AM MDT Thu Jul 18 2024

Lingering light showers will continue through the morning but
should have minimal impact on TAF sites with VFR conditions and
CIGS well above ILS breakpoints. Scattered showers and storms
are expected to develop over the high terrain after 18Z today
with some southeastward drift into adjacent lower elevations
especially along the divide and across the southwest Colorado
valleys. VCTS is possible at KTEX, KASE, KGUC, KEGE and KDRO
with gusty outflow winds and brief MVFR at times. Otherwise,
most lower valleys should remain on the drier side with VFR
prevailing under partly sunny skies with generally light,
terrain driven winds.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

SHORT TERM...MDA
LONG TERM...DB
AVIATION...MDA