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786
FXUS65 KGJT 201106
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
506 AM MDT Fri Sep 20 2024

.KEY MESSAGES...

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- Dry conditions today with near to slightly above average
  temperatures.

- The next system arrives tomorrow bringing scattered to
  widespread showers and storms as well as a reinforcing shot
  of cooler air.

- Some of the Colorado mountain ranges above 10,000 feet could
  receive 1-3 inches of snow. The central mountains look to be
  favored for the highest totals where up to 6 inches is
  possible.

- The weather pattern remains cooler and unsettled early to mid
  next week as additional disturbances move through, providing
  at least scattered shower activity.
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&&

.SHORT TERM /THROUGH SATURDAY NIGHT/...
Issued at 321 AM MDT Fri Sep 20 2024

Today will be relatively quiet with some passing clouds across the
south and temperatures warming a few degrees. Attention turns to the
next system, which is currently over southern California. This low
pressure lifts northeastward towards the Four Corners tonight before
passing over the forecast area tomorrow. Lift associated with this
system is rather modest and it will result in scattered to
widespread showers by tomorrow afternoon. Gulf of Mexico moisture
will be pulled in from the south and southeast ahead of the low,
while Pacific moisture arrives with the low itself. PWAT values
reach 150-200 percent of normal during the peak of the storm. There
are signs of CAPE in the warm sector tomorrow afternoon, which
supports scattered thunderstorms as well. On Saturday morning the
low approaches the Four Corners so expect precipitation development
to occur across the southern half of the forecast area. Showers and
storms will spread north and east as the low tracks overhead
eventually reaching the Wyoming state line in the late afternoon.
The low drifts over central Colorado tomorrow night, which keeps the
precipitation going for the northeast half of the CWA overnight. The
coverage of showers begins to decrease Sunday morning.

Given the track of the low...the best moisture funnels into the
central mountains, which happens to be co-located with the strongest
lift. Model QPF is showing that some places could get over an inch
of liquid in those spots. The other flip side to this system is
snow. The cooler air associated with this storm will drive snow
levels down to 11-12 kft. With the increased potential for
convection...snow levels could drop to as low as 10 kft. In general
the snow amounts are 1-3 inches with localized amounts as high as 6
inches. The Sawatch and Elk mountains look to have the highest
totals with lesser amounts for the other Colorado ranges. Impacts at
pass level should be minimal with the warm roads temperatures, but
slushy conditions could not be ruled out. Wrap around northwest flow
will keep some light snow lingering through Sunday morning over the
peaks with light rain in the lower elevations along the Divide,
before clearing out by Sunday afternoon. Those with plans to go
above tree line on Saturday be ready for a drastic change in weather
once the precipitation begins.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
Issued at 321 AM MDT Fri Sep 20 2024

The cutoff low ejects into the Plains by Sunday afternoon, with
drying conditions across eastern Utah and western Colorado. Even as
we dry out here on Sunday, the next trough will be dropping into the
Northern Rockies and digging into eastern Utah and western Colorado
by Monday evening. This will bring a return to unsettled conditions
across the Western Slope. This is also the point where model
agreement begins to diminish, with some guidance wanting to develop
another cutoff low over the Four Corners that retrogrades toward the
Mexican border,while building a ridge into the Northern Rockies,
forming a Rex Block. Other guidance keeps this trough open and
scoots it out into the Plains by midweek. By the forecast for
Wednesday, guidance is all over the place. Some solutions keep
eastern Utah and western Colorado cooler and unsettled, some build
in a ridge from the east, and all kinds of variation in between.
Hopefully things will come into agreement in the coming days. In the
meantime, eastern Utah and western Colorado can expect unsettled
weather and temperatures around 5 degrees below normal to continue
through the period.

&&

.AVIATION /12Z TAFS THROUGH 12Z SATURDAY/...
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Issued at 505 AM MDT Fri Sep 20 2024

VFR conditions and light terrain-driven winds are expected
through the taf period.
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&&

.GJT WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

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