554
FXUS65 KGJT 041137
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
437 AM MST Thu Dec 4 2025

.KEY MESSAGES...

- Prolonged moist northwest flow will bring a threat of
  accumulating snow to the mountains and adjacent valleys
  tonight through early Sunday.

- The first round will mainly impact the northern Colorado
  mountains late this evening through tomorrow afternoon with a
  greater than 70 percent probability of 4 inches or more of
  snow over the Elkhead and Park Ranges.

- The snow will be more widespread and be accompanied by
  stronger winds at the high elevations Friday night into early
  Sunday. The northern and portions of the central Colorado
  mountains have a greater than 50 percent probability of 8
  inches of snow. Travel impacts including possible road
  closures should be planned for.

&&

.SHORT TERM /THROUGH FRIDAY/...
Issued at 307 AM MST Thu Dec 4 3075

With a moderately strong Madden Julian Oscillation now located
in the Western Hemisphere the models have responded with a
robust northwest flow pattern across the PacNw to the Central
Rockies. The strength and location of the MJO most likely has
some effect on the persistent arrival of atmospheric river
moisture to the West Coast. So the bottom line...strong and
persistent moist northwest flow means our northern and portions
of central Colorado mountains are about to make up for the slow
start to the snowpack season. The forecast challenge in this
pattern remains the same...timing of lulls between events...and
underestimating the effectiveness of cold northwest orographics
on snow totals. With that said the first guess is in which is
to go with an early round advisory favoring the Elkhead and Park
Ranges late this evening through tomorrow afternoon with the
arrival of the first batch of moisture and modest ascent with a
passing wave tomorrow morning. The best snow rates look to be
around sunrise through early afternoon then a brief `lull"
through the evening before we introduce stronger moisture
advection arriving on a stronger jet aloft. This first round
looks to bring a good 4 to 8 inches to the above mentioned
ranges with 1 to 4 over the Flat Tops into the Gore and central
mountains. Unfortunately this pattern will leave the southern
mountains out for any significant accumulations. For nearer term
weather another cool but sunnier day for most the area is
expected today in the wake of the passing storm. The high
country and especially the northern spine mountains will hang
onto orographic clouds and occasional flurries through at least
early afternoon.

&&

.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
Issued at 307 AM MST Thu Dec 4 3075

For the long-term forecast, the models are in good agreement
through about Tuesday with the high pressure sitting well off
the California coast keeping eastern Utah and Western Colorado
under a strong northwesterly flow allowing a series of
shortwaves to drop down through the Pacific Northwest into the
region. Additionally there is some atmospheric river (AR) action
to supply some moderate moisture into the region this weekend
with these shortwaves and more significant moisture by mid next
week. The models do start to diverge by Tuesday with the
European AI ensemble and deterministic models progressing the
high to the east into the Desert Southwest while the GEFS keeps
it pretty much in place and the deterministic GFS even
retrogrades it to the west. Current guidance favors the European
solution turning the flow aloft westerly with temperatures
warming to ten or more degrees above normal by mid week and
precipitation coming as rain showers in the lower elevations
below about 7,000 ft. Though this is the favored solution,
confidence is still low at this point beyond Tuesday, and with
the strong AR possible we could see another significant winter
storm in the northern mountains. Definitely stay tuned on this
one.

With that said, we won`t see a lot of moisture, pwats around 0.50
inches, but will see moderate AR flow Friday night into Saturday
with integrated water-vapor transport (IVT) values of 150 to 250
kg/m/s driving by the strong northwest flow aloft with H500 winds
running 60-70 knots. Though there is a bit of upper level dynamics
with a weak jetstreak moving overhead, this strong northwesterly
push will provide good orographic lift to drive the snow showers
across the northern and central Colorado mountains. A Winter Storm
Watch is in place for Elkhead, Park, Gore and Elk Mountains, and for
the Flat Tops and central mountain valleys Friday evening through
Sunday morning for 10-20 inches snow up north with 40 mph winds, and
five to 14 inches snow along and south of I-70 with 35 mph winds.
Check for updates on this over the next day or so as the forecast
becomes more certain to see if these watches will be upgraded to
Winter Weather Advisories and/or Winter Storm Warnings. Either way,
expect winter driving conditions on the northern and central
mountain roads and passes this weekend.

With the northwesterly flow continuing into early next week, expect
continued light orographic snow showers mostly across the northern
mountains as weak shortwaves brush by to the north. Moving into mid
next week, though confidence is low, models are predicting a strong
AR to move into the northern areas with IVTs of 200 to 300 kg/m/s
and pwats approaching 0.70 inches. With the nose of a strong jet
pushing down providing good upper-level dynamics, we could see
thunderstorms in the lower elevations north of I-70 and heavy snow
and possible thundersnow in the mountains. A lot can change with
this one, especially if it decides to shift a bit farther south, so
stay tuned for updates.

&&

.AVIATION /12Z TAFS THROUGH 12Z FRIDAY/...
Issued at 437 AM MST Thu Dec 4 2025

So far MVFR cigs at some of the TAF sites have been the biggest
impacts overnight with minimal reports of fog. The lower cigs
are likely to stick around through at least mid morning before
clinging mainly to the high peaks. So VFR and light winds should
dominate the afternoon and evening forecast. Another system
arrives to the north late this evening and will spread ILS cigs
to some sites during the early morning hours. KHDN is the most
likely terminal to be impacted by snow in the predawn hours.
Snow will favor the higher peaks of the northern Colorado
mountains but widespread terrain obscuration from cloud across
the central and northern mountain is expected well into Friday
and beyond.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

CO...Winter Weather Advisory from 11 PM this evening to 5 PM MST
     Friday for COZ004.
     Winter Storm Watch from Friday afternoon through Sunday
     morning for COZ004-010-013.
     Winter Weather Advisory until 5 AM MST early this morning for
     COZ023.
UT...None.

&&

$$

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