166
FXUS65 KGJT 232009
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
209 PM MDT Sun Jun 23 2024

.KEY MESSAGES...

- Scattered showers and thunderstorms will continue through
  sunset, with a few stronger storms possible north of I-70. A
  low but persistent threat of flooding with slow moving and/or
  training storms remains.

- A rinse and repeat pattern will continue into the coming week,
  with temperatures 5-10 degrees above normal and afternoon
  convection over the higher terrain.

- A push of deep subtropical moisture looks to move in mid week,
  bringing a return to widespread thunderstorms with an
  increasing flash flood threat. Drying will follow for the
  weekend.

&&

.SHORT TERM /THROUGH MONDAY/...
Issued at 205 PM MDT Sun Jun 23 2024

Dry air continues to move in aloft as the subtropical high slides
into the Desert Southwest today and pushes a ridge overhead. The
amount of surface moisture has definitely begun to diminish, as
evidenced by dew points running around 10 degrees lower than this
time yesterday across the area. Where yesterday we saw dew points in
the 50s and low 60s, today we`re seeing upper 40s to low 50s. This
is still plenty of moisture to get convection going, however, as
evidenced by the showers and thunderstorms already firing off the
terrain, and with this morning`s 12z GJT sounding`s PWAT at nearly
an inch, there`s enough moisture still in the column to produce some
heavier rains. However, the environment overall is just not as
favorable to severe thunderstorms as we`ve seen the last several
days. Instability values have come down into the 500-1000 J/kg
range, and effective bulk shear has decreased to just 20-30 knots.
These modest parameters combined with some enhanced lift from a
passing shortwave has led to the strongest convection firing over
the Tavaputs in eastern Utah and western Colorado. Unfortunately,
even with the passing shortwave, steering flow is much weaker today,
meaning that these cells have been slow moving and also have been
training over the same areas. This means that, in areas where these
slow moving storms set up, there is a higher than normal threat for
flash flooding. So while severe thunderstorm warnings aren`t as
likely this afternoon, flood advisories and/or flash flood warnings
are a distinct possibility.

The shortwave looks to slip east of the Divide this evening and with
the coincident loss of daytime heating, look for convection to die
off and skies to clear. As the subtropical high continues to build
and expand into the Desert Southwest, warm air will build in as
well. Despite the clearing skies and decreasing surface moisture,
tonight is actually forecast to be a few degrees warmer thanks to
the building heat dome overhead, with tomorrow`s nearing 10 degrees
above normal. High temperatures today and tomorrow will run around 5
degrees above normal, with some triple digits sneaking in for the
lowest desert locations in eastern Utah. Areas that see convection
today and tomorrow afternoon will run a few degrees cooler, however.

Another weak shortwave looks to round the high and pass overhead
again tomorrow afternoon, but parameters look even worse with the
high pressure building. Enough surface moisture should stick around
that convection will once again fire off the higher terrain, and
with slow steering flow, the threat for heavy rain and flooding will
continue into tomorrow afternoon. Skies should clear after sunset
with loss of heating, but overall it looks like another rinse and
repeat kind of day.

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
Issued at 205 PM MDT Sun Jun 23 2024

Tuesday will be the warmest day of the week as the high pressure
becomes centered over New Mexico. Afternoon convection is expected
once again with little change in the moisture. As the trough
approaches the West Coast Wednesday, it impinges on the the western
flanks of the ridge causing moisture from the Mexican Plateau that
had been kept west of the region to begin drifting northward over
the forecast area. As result we will see an increase in coverage and
intensity of convection across the area. This activity looks to
linger into the overnight hours. On Thursday, the moisture peaks
with PWAT values over one inch for much of the region. During this
period the potential for heavy rainfall becomes elevated. As the
trough moves across the Pacific Northwest to the northern Rockies on
Thursday night then to the northern High Plains on Friday, the
moisture tap from the south is shunted to the east allowing drier
air to infiltrate in the west flow behind the trough. Consequently,
the area should see a downturn in moist convection on Friday with
even less shower/thunderstorm activity Saturday as drying continues.

Temperatures are expected to remain 5 to 10 degrees above normal
Tuesday and Wednesday with readings in the low 100`s forecast for
the Grand Valley and the lower elevations of southeast Utah.
However, increased clouds and shower coverage is expected to bring
temperatures to near normal levels Thursday with a slow rise
coinciding with drying Friday and Saturday.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1114 AM MDT Sun Jun 23 2024

Expect mostly VFR conditions and light winds through the TAF
period. The exception will be convection starting now over the
higher terrain, drifting into adjacent valleys and winding down
after 00Z. Look for scattered showers and storms over the
southern mountains with more isolated coverage as you go north.
Included VCTS in KTEX and KDRO, but not enough certainty to
include it in any other TAF`s, though most mountain sites have
some minimal risk through the afternoon.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

SHORT TERM...BGB
LONG TERM...KJS
AVIATION...TGJT