427
FXUS65 KGJT 192042
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
242 PM MDT Sat Oct 19 2024

.KEY MESSAGES...

- A strong closed low pressure system will wobble over Arizona
  before kicking northeast across central Colorado late
  tomorrow. This keeps heaviest precipitation concentrated over
  the Four Corners region through tomorrow and where the focus
  for thunderstorm development will be.

- Moderate to heavy snowfall rates will continue to impact
  travel conditions over southern Colorado`s mountain corridors.
  Snow is most likely to accumulate on roadways during the
  overnight hours with improvement during the afternoons.

- Cold air settling in behind the system as conditions dry and
  clear could lead to freezing temperatures in some of the
  southern valleys and some pockets of the White and Yampa
  River Basins.

&&

.SHORT TERM /THROUGH SUNDAY NIGHT/...
Issued at 242 PM MDT Sat Oct 19 2024

I`m kinda done with this upper low but unfortunately it is not
done with us. The 12Z H500 hand analysis map had it centered
right over AZ with minimal height changes surrounding it...hence
it is still spinning there in the latest satellite pictures.
Clearing/darkening in the water vapor has progresses around the
base of the low and is lifting on the upstream side this
afternoon where a strong PV lobe is located. More
organized/heavier precipitation will be lifting northward across
the 4 Corners as upright convection is released by the dynamic
trop nosing into the northeast AZ. As this lobe continue to
rotate back to the West overnight the area of heavier
precipitation should follow and with cooler temperatures aloft
moving in...snow production and lowering snow levels should keep
a heavy snow threat into the southern San Juans through
sunrise. The PV lobe folding into the system will deform and
push it slightly northward overnight but it does not look to
start a more eastward trajectory until late tomorrow afternoon.
So southerly flow/orographics will continue to feed into the
southern San Juans and have left the warning in place even after
the prolonged lull we have had today. The impacts just haven`t
been there for the northern San Juans and most elevations below
10000 feet. The high snow levels have also eaten away at snow
totals from earlier thinking. This system isn`t overly cold and
it still looks like the sun angle will help melt roadway snow
during the afternoon hours tomorrow and have opted to downgrade
the warning for the northern San Juans to an advisory...probably
a day or two too late in hindsight. The system accelerates
tomorrow night and lingers just across the central high mountain
during the morning hours on Monday. There could be some impact
to the high passes early Monday from snow but overall not
confident enough to hoist additional winter headlines as this
storm becomes more progressive. Probability are increasing for
possible freezing conditions across the southern valleys Monday
morning. Again however clouds and lingering moisture will be big
factors so will continue to monitor this. Otherwise slightly
cooler temperatures push northward tomorrow as the thicker
clouds and precipitation spread farther north. Across the far
northern CWA...this trend looks to warm as the post frontal
airmass will be further eroded.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
Issued at 242 PM MDT Sat Oct 19 2024

By Monday morning, the low pressure system will have exited stage
right across the Divide and out onto the Front Range as it makes its
way on to the Plains. Can`t rule out a lingering shower along the
Divide in the central and northern Colorado mountains into the
afternoon with no expected impacts. Behind the low, ridging tries to
move in from the west, but longwave troughing across southern Canada
pretty much keeps any ridge knocked down through the coming week
resulting in a dry zonal flow aloft. This zonal flow will bring a
return of dry warm weather to eastern Utah and Western Colorado.
There will be enough subsidence to clear out the skies Monday and
keep skies mostly clear through the week. The only exception will be
some bands of high clouds passing across the region as a shortwave
pass well to the north late Tuesday into Wednesday and again towards
the end of the week. Temperatures will start the week near normal to
about five degrees below normal, warming to five to ten degrees
above normal by Wednesday where it will remain going into next
weekend.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1147 AM MDT Sat Oct 19 2024

Showers continue with snow above about 9000 ft across southwest
Colorado and southeast Utah today as the storm system remains
over Arizona. Mountain terminals like KTEX ad well as adjacent
southern valleys like KDRO will see below breakpoint conditions
throughout the next 24 hours with lower CIGS and VSBY in
showers. North of the San Juans, there are mostly mid level
clouds with VFR conditions, the exception being KHDN where a low
deck hangs in the valley with ceilings below breakpoints. Expect
these KHDN ceilings to lift through the afternoon. Clouds and
showers increase overnight into Sunday morning, spreading
north as the storm system finally moves northeast towards the
Four Corners and eventually tracks across western Colorado
during the day on Sunday.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

CO...Winter Weather Advisory until 9 PM MDT Sunday for COZ018.
     Winter Storm Warning until 9 PM MDT Sunday for COZ019.
UT...None.

&&

$$

SHORT TERM...15
LONG TERM...DB
AVIATION...TGJT