571
FXUS65 KGJT 180435
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
1035 PM MDT Tue Sep 17 2024

.KEY MESSAGES...

- Strong and gusty winds will continue through sunset, then
  decrease and transition to a light drainage flow during the
  remainder of the night.

- A cold front sweeping through the area will keep temperatures
  cooler than normal for the next several days.

- Expect a break in the action Wednesday and Thursday before
  another system impacts the region this weekend.

&&

.SHORT TERM /THROUGH WEDNESDAY NIGHT/...
Issued at 405 PM MDT Tue Sep 17 2024

As of 21Z, the cold front associated with the strong storm
system centered over southeast Idaho, extended from 30EW KRIW to
K4V0 to just west of KCNY. Meanwhile, ahead of the front a dry
slot eroded subtropical moisture over eastern Utah and much of
western Colorado. Shower activity declined significantly from
its peak earlier in the day with just a couple of storms over
the San Juan Mountains and a line of showers and weak storms
extending from the Roan Plateau northeast of Grand Junction to
the northeast across Craig and onto Dixon.

This activity is expected to dissipate pretty rapidly during the
late afternoon hours as the vorticity lobe rotating north-
northeastward across northwest Colorado passes north of the
forecast area. The influx of dry air is expected to bring mean
PWAT values across the forecast area to between 0.3" over
eastern Utah to 0.5" over the Continental Divide according to
HREF. In response to drying and subsidence in the wake of the
vort lobe, only a handful of showers/storms will linger over the
Continental Divide before 02Z/Wed. The closed low lifts
northeast overnight pushing over the northern High Plains by
12Z/Wed. In its wake, a transitory short wave ridge forms. This
combined with drier air will lead to clear skies for all but the
northernmost zones overnight. Strong radiational cooling,
diminishing winds and the influx of colder air will lead to
significantly cooler temperatures overnight with readings coming
in around 10 degrees cooler than those recorded this morning.

Another closed low moves over the San Francisco Bay area on
Wednesday, though this feature won`t figure directly into
weather conditions over eastern Utah and the West Slope until
later in the week. Modestly breezy southwest winds develop
across the area in the afternoon under mostly sunny skies. Dry
air continues to move over the area throughout the day, so there
is little to no chance for moist convection Wednesday afternoon
or Wednesday night for that matter. Highs Wednesday afternoon
will be cooler than today, dipping below normal for most
locations. Similarly, overnight lows will run below normal and
could approach freezing for some lower elevation spots in
northwest Colorado.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
Issued at 405 PM MDT Tue Sep 17 2024

Models were in good agreement Thursday morning with the Pacific
low turning inland south of San Francisco tracking for northern
Arizona. Though they continue to agree on the track of the low
across northern Arizona before ejecting to the northeast across
the Four Corners and southern Colorado and out onto the Plains,
they diverge on the timing with the GFS and Canadian models
putting the low over the Four Corners Saturday morning and the
European running about nine hours behind. The ensemble means
show a similar timing difference with a lot of dispersion among
the members, so positioning of both models lay within the margin
of error. Guidance is leaning more to the GFS solution with the
faster track. This system carries a little moisture with it,
0.5 to 0.6 inches pwat, enough to spawn isolated nocturnal
storms over the southern and central mountains overnight Friday,
spreading north into the northern Colorado mountains Saturday
morning. Coverage along the Divide in the central and northern
Colorado mountains becomes more scattered to numerous in the
afternoon as moisture from the Front Range wraps around the low.
A few showers may linger along the Divide overnight Saturday
before coming to an end Sunday as the low pushes east out of
Colorado. Beyond Sunday, models diverge wildly, but generally
agree on ridging building in along the Rockies. Temperatures
will be near normal Thursday and Friday, cooling three to five
degrees below normal Saturday with the trough passage and slowly
warming back to normal Monday and Tuesday of next week.

&&

.AVIATION /06Z TAFS THROUGH 06Z THURSDAY/...
Issued at 1034 PM MDT Tue Sep 17 2024

VFR conditions are in place with with winds finally settling down to
lighter drainage patterns. Winds will remain relatively light though
a few gusts near 25 mph could occur by peak heating hours on
Wednesday and persist through sunset.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

SHORT TERM...NL
LONG TERM...DB
AVIATION...TGJT