835
FXUS65 KGJT 021113
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
513 AM MDT Tue Sep 2 2025

.KEY MESSAGES...

- Isolated afternoon showers and thunderstorms develop along and
  east of the Divide today with more scattered thunderstorms
  over the San Juans.

- Temperatures trend about 5 degrees above normal through
  Wednesday before a cooler and more active storm system moves
  in by Friday.

- More widespread precipitation is possible on Friday and into
  the weekend as rich extra-tropical moisture moves into the
  region with a potential for heavier rain on the recent fire
  scars.

&&

.SHORT TERM /THROUGH WEDNESDAY/...
Issued at 242 AM MDT Tue Sep 2 2025

The synoptic pattern is dominated high pressure over the Great Basin
extending east over Rocky Mountains with troughing across the Plains
and Eastern States, and a low pressure system/troughing over the
Eastern Pacific in a weak omega-ish block. This high pressure will
keep eastern Utah and Western Colorado under mostly clear skies
through today and Wednesday. The exception to this will be some
moisture that slides into the San Juan Mountains from Arizona under
the high pressure and a bit of moisture from the Front Range pushing
west to the Divide. Weak upper-level dynamics of a right entrance
region of a jet streak and strong diurnal heating will enhance
convection across the San Juans and east of the Divide over what we
saw yesterday. This will bring mostly isolated showers with a few
embedded thunderstorms along and east of the Divide, and scattered
thunderstorms over the San Juan Mountains through the afternoon
hours. These storms will end by evening under the subsidence of the
high and with the setting sun. Temperatures today will be a few
degrees above normal in the mountains and about five degrees above
normal in the lower valleys. Wednesday will see very similar
temperatures but weaker convection with the region loosing the upper-
level dynamic support as the jet streak shifts east.

&&

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

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 /12Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 508 AM MDT Tue Sep 2 2025

Expect mostly VFR conditions and light terrain driven winds
across the region through the TAF period. The exception will be
isolated to scattered afternoon showers and thunderstorms over
the San Juan Mountains in southern Colorado extending north
along and east of the Divide. Included a Prob30 group in KTEX
and KDRO TAF`s for a slight chance of impacts, mostly gusty
outflow winds and lightning.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

SHORT TERM...DB
LONG TERM...BGB/DB
AVIATION...DB