113
FXUS65 KGJT 282355
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
555 PM MDT Fri Jun 28 2024

.KEY MESSAGES...

- Afternoon/evening showers and storms expected again today
  though coverage and intensity will be less than seen over the
  last few days.

- Drier air moves in Saturday for a brief downturn in shower and
  storm activity though some convection is expected along the
  Continental Divide. Temperatures will run around 5 degrees
  above normal.

- Deep subtropical moisture returns Sunday onward, with a return
  to widespread convection and increased chances for flash
  flooding.

&&

.SHORT TERM /THROUGH SATURDAY/...
Issued at 204 PM MDT Fri Jun 28 2024

This mornings sounding reported 1.01 inches of PWAT here at the
Grand Junction airport. This matches up fairly well with
forecast amounts so subtropical moisture does continue to linger
across eastern Utah and the Western Slope. Much drier air can
be found to our north and west and has started advecting into
the area, however. Despite this intrusion of drier air, we can
still expect some afternoon showers and storms. Speaking of,
cells have just started popping across the CWA as forecast by
CAM models. Upper level support is lacking though there is some
weak divergence aloft that will help with lift outside of
daytime heating. SPC`s Mesoanalysis Analysis page is
highlighting widespread values of 500 to 1000 J/kg of CAPE, down
from 1500 J/kg that was showing up in earlier model runs. This
is good news as storms shouldn`t be as strong as what we`ve seen
over the past few days. The highest shear is found across the
northern half of the CWA and also across much of eastern Utah.
The 18Z HRRR run continues to show the best coverage to be north
of the I-70 corridor though some cells do fire over eastern
Utah and SW CO. In this environment, we will continue to see
some hail, gusty outflow winds and heavy rainers though not as
intense as what we experienced yesterday. The convection will
continue into the early evening hours before starting to weaken.
Thus, the Marginal Risk (5% chance for wind >= 58 mph and/or
hail >= 1 inch) for severe thunderstorms issued by SPC for the
northern half of our forecast area. Showers and a few storms
will likely persist for an hour or two after midnight before
dying off completely.

PWATs finally drop down to 0.6 to 0.8 inches across the area for
Saturday and CAM guidance is picking up on this downturn with less
convective coverage. Having said that, the higher terrain will be
favored for convective initiation with the San Juans and areas
along and around the spine of the Continental Divide also being
favored for showers and storms. The NBM agrees with slight
chance to chance there (20 to 50%) along the Divide but little
elsewhere. Probably underdone and may need to bring in the HRRR
or NAMNEST to bump PoPs for the remaining higher terrain. Will
change as needed. As the atmosphere will be drier than seen
today, gusty surface winds will be probable along with some
hail. Heavy rain will be possible as well, under and near the
strongest convection, but widespread heavy rain appears less
likely. Enjoy this reprieve, brief as it is, because the next
surge of moisture starts Sunday.

&&

.LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/...
Issued at 204 PM MDT Fri Jun 28 2024

The persistent monsoonal regime stays put Sunday and Monday, along
with the oblong high pressure anchored over the southern states. The
pending arrival of a PACNW trough nudges the subtropical moisture
plume eastward enough to keep some of our northern counties out of
the crosshairs. This doesn`t mean a dry forecast, because fringe
moisture interacting with a strong southwesterly jet max Sunday
afternoon should get things going on the terrain of the Tavaputs,
Flat Tops, Elkheads, etc. up there. Meanwhile down south, where the
moisture is best, there should be no problem with another round of
robust convection around the Four Corners, Central Mountains and the
San Juans. The trough axis works across the Great Basin Sunday night
and should keep some active weather going during the overnight hours
into Monday morning. Leftover cloud cover on Monday leaves some
forecast uncertainty to the level of convective instability we might
see. Moisture will remain abundant, as well as the presence of the
dynamic forcing under the now broadened open wave working across the
northern Rockies on Monday afternoon. For now, it`s best to expect
more monsoonal showers and thunderstorms for the forecast Monday and
likely Tuesday too. Shower activity Tuesday looks to turn down as
the upper trough moves eastward, kicking the subtropical return on
the high back onto the Plains and thereby dries us back out under
northwesterly flow spilling in from the PACNW. Another trailing wave
ripples through Wednesday with little new moisture to work with.
Remnant moisture will get worked on and likely spark a shower or two
down in our southern counties and along the southern Divide again. A
break in the unsettled weather pattern finally arrives in time for
Fourth of July festivities as the trough on the Plains suppresses
the high enough to shut off the monsoonal feed and introduce some
dry air from the northwest. This trend holds for Friday and perhaps
beyond as high pressure amplifies over the West. Temperatures surge
upward Sunday before cloud cover and precipitation bring them down
some Monday and Tuesday. The late week dry pattern should see the
return of warmer conditions as well. The big wheel of the monsoon
keeps turning. Stay tuned.

&&

.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
Issued at 555 PM MDT Fri Jun 28 2024

Scattered showers and thunderstorms continued to move eastward
north of the Roan Plateau into the Flat Tops with another area
of activity in the vicinity of KHDN. It appears likely that in
addition to storms in the vicinity, KHDN will likely see a brief
shower, though VFR conditions will persist. In fact, VFR
conditions are expected for all TAF sites during the next 24
hours and it`s unlikely that any of the other TAF sites will see
a thunderstorm threat. Gusty outflow winds with today`s storms
have been far less intense than yesterday with the highest
observed 45 mph. Storms will dissipate this evening with
clearing occurring overnight. The region will see fewer showers
and thunderstorms on Saturday afternoon. Winds will shift to a
light drainage flow toward late evening, switching to normal
upslope flow on Saturday afternoon.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

SHORT TERM...TGR
LONG TERM...LTB
AVIATION...NL