112
FXUS65 KGJT 182237
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
437 PM 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 late in 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 also keep a threat of new wildfire starts in
  the picture.

&&

.SHORT TERM /THROUGH FRIDAY NIGHT/...
Issued at 248 PM MDT Thu Jul 18 2024

The persistent area of high pressure is currently centered near
west-central New Mexico / east-central Arizona this afternoon,
resulting in another round of diurnally-driven showers and
thunderstorms across the Western Slope. Convection has been
slightly stronger than this time yesterday with some pea-sized
hail and a quick three-tenths of an inch of rain reported on the
Uncompahgre Plateau. Even with a PWAT less than the mean value
of 1.43 inches on this morning`s 12Z GJT sounding, what moisture
remains trapped in the atmosphere is more than sufficient for
producing storms today, as well as keeping the brief potential
for slightly heavier rainfall rates present. The ridge will
begin to slowly retrograde westward tonight and into Friday,
allowing today`s precipitation to largely diminish overnight
before activity redevelops by midday Friday. We are expecting a
slight uptick in storm coverage on Friday as a shortwave trough
rounding the backside of the main low to the east brushes the
Continental Divide. PWATs will increase to 120 to 150 percent of
normal which could bring better potential for heavier rain.
Even so, the low levels will remain dry so gusty outflow winds
and small hail will be the primary concerns from convection.
Friday night looks to be quiet though a lingering shower cannot
be ruled out.

Temperatures through the short term won`t fluctuate much given
the continued presence of the ridge overhead. Overall, readings
will trend slightly above normal for the lower elevations and
near normal in the mountains. Overnight lows tonight and Friday
night will be mild for mid July.

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...
Issued at 248 PM MDT Thu Jul 18 2024

Anomalously low heights will be settling in East of the Rockies
which will drive the SubTropical High well back to the West into a
least the middle of next week. Ensemble anomaly tables show higher
than normal PWAT extending north of the Gulf of Cali into the
eastern Great Basin...effectively shutting down a direct tap to the
monsoon into the Rockies. Instead we will continue to advect
recycled moisture through the ridge which will keep the daily
thunderstorm chances in the forecast but limit the widespread heavy
rainfall and flood threat. I would have to guess that extended
scenario will be similar to the past few days in the northerly flow
pattern. Storms should favor the higher terrain for initiation and
drift southward as they regenerate with a few storms surviving into
adjacent valleys. Overall the precipitation outlook for the many of
the lower valleys is not favorable and it will be very hit or miss
as storms move off the hills. There is some hope that by late next
week a stronger system arriving the PacNW will begin to nudge the
high eastward and this could lean the moisture plume farther into
the Great Basin. Temperatures remain fairly static and will continue
to run near to above normal through the period.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 435 PM MDT Thu Jul 18 2024

Scattered showers and storms will continue for the next several
hours. Gusty winds will be the main impacts with low chances
for MVFR conditions. A few showers may linger overnight.
Scattered showers may develop around 12Z for sites along I-70
with more storms expected in the afternoon.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

SHORT TERM...MMS
LONG TERM...15
AVIATION...TGJT