070
FXUS65 KGJT 012032
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
232 PM MDT Mon Sep 1 2025

.KEY MESSAGES...

- Showers and thunderstorms continue on the San Juans today and
  then begin expanding up the Divide on Tuesday with the San
  Juans favored for better coverage.

- Temperatures trend nearly 5 degrees above average through mid
  week then cool with a potentially more active storm cycle.

- More widespread precipitation is possible on Friday and into
  the weekend, given the potential for rich extra-tropical
  moisture.

&&

.SHORT TERM /THROUGH TUESDAY NIGHT/...
Issued at 232 PM MDT Mon Sep 1 2025

Remnants of a weak jet streak and shortwave boundary remain
across the southern San Juans to north central New Mexico, which
is allowing thunderstorms to fire along the southern San Juans
with a southerly drift into the valleys below along the Highway
160 corridor. Expect this to continue through the evening before
storms taper off by midnight with the HRRR picking up on this
activity pretty well. Coverage is expected to remain isolated to
widely scattered. The 18Z sounding indicates a dry profile so
gusty outflow winds and lightning are the primary concerns
although a brief downpour cannot be ruled out since enough
moisture remains down south. Elsewhere, conditions are expected
to remain dry outside of the southern San Juans and adjacent
valleys as the ridge axis of high pressure continues to build
overhead. This will be a similar story on Tuesday, although a
little bit more moisture sneaks in across the south for a bit
more coverage of storms but San Juans still remain the likely
candidate for this activity but coverage could creep up along
the central divide. Don`t expect activity to be long lived or
sustained due to subsidence under the high pressure and lack of
shear. Outside of that, dry conditions should prevail.
Meanwhile, high temperatures both today and Tuesday will trend a
bit warmer with highs in the 90s for the lower valleys of
eastern Utah and west-central Colorado with 80s among the
remaining higher valleys...which is around 5 degrees or so above
normal.

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
Issued at 232 PM MDT Mon Sep 1 2025

By Wednesday, the ridge over the Intermountain West will
elongate in response to a wave rotating around an area of low
pressure off the Pacific Northwest Coast. For Eastern Utah and
Western Colorado, this won`t result in much of a sensible
change, as sunshine and above normal temperatures will continue
to be the rule through the end of the week. But this is the
first sign of the next pattern shift. A pool of rich moisture
will be drawn up between the trough and the ridge, initially
into the western Great Basin. But as the trough rotates through,
it will nudge the ridge overhead slightly eastward, so that by
Thursday moisture will begin sneaking into southeast Utah and
southwest Colorado. In response, showers and thunderstorms will
become more widespread Thursday afternoon, although still tied
to the terrain, favoring the San Juans most. The moisture will
continue to increase through the weekend, peaking Saturday and
Sunday, bringing more widespread precipitation and cooler
temperatures. Model guidance agrees pretty well on those two
facts, but there is quite a lot of discrepancies between
different model suites at the moment. Currently, the ECMWF and
it`s ensembles are favoring a more typical monsoonal pattern
where the moisture oozes in on the back side of the ridge and we
see daily showers and thunderstorms. The GFS suite on the other
hand, particularly the current deterministic run, wants to
bring some tropical influence into the situation. The GFS brings
a tropical disturbance, or at least the remnants of it,
northeast through New Mexico, and has it phase with energy
rotating around the Pacific Northwest low. Things could get
interesting if this forecast verifies, but as it stands,
forecast confidence on anything more detailed than "we`re moving
into a cooler and wetter pattern" is pretty low. Stay tuned
though, as these discrepancies should work themselves out in the
next few days.

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1152 AM MDT Mon Sep 1 2025

VFR conditions will prevail for the next 24 hours for much of
the area as drier air will lead to mostly sunny skies. Some
cumulus is building over the San Juans with potential for
isolated to widely scattered showers and thunderstorms this
afternoon. Some of these storms could drift south off the
terrain into the southwest Colorado valleys, particularly KDRO
to KPSO after 00Z. Therefore, included a PROB30 group for -TSRA
at both KTEX and KDRO with brief MVFR possible if a brief shower
occurs. Expect mainly gusty outflow winds with brief downpour
and small hail also possible.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

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