Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 221122
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
522 AM MDT Fri Mar 22 2024

.KEY MESSAGES...

- A weak disturbance late this afternoon and evening will bring
  light mountain showers to the northern tier of the area. Rain
  below 8000 feet, snow above 8000 feet, and can`t rule out a
  few rumbles of thunder, with minimal accumulations.

- High temperatures of 5-10 degrees above normal linger through
  Saturday, with mostly to partly sunny skies.

- A more impactful storm system is expected to bring widespread
  precipitation, including mountain snow, along with cooler
  temperatures from Saturday night through Sunday night.

- Cooler and unsettled conditions continue into next week.

&&

.SHORT TERM /THROUGH SATURDAY/...
Issued at 336 AM MDT Fri Mar 22 2024

Shower activity overnight is winding down as the shortwave has moved
southeast out of the region. The clouds are dissipating under the
subsidence of the shortwave ridge moving in to eastern Utah and
Western Colorado from the west with the remaining clouds mainly in
the mountains where the northwest flow is still producing upslope
conditions. These clouds are indicative of the abundant low-level
moisture still lingering in the region. The models are in good
agreement, but are running fast, placing the center of the low about
200 miles closer to the Oregon Coast than its current position per
satellite imagery. At the same time, the models are holding the
ridge back to the west over central Oregon and Washington as apposed
to it position along the Idaho Border pushing into Idaho, but then,
its`s harder to pick out the ridge axis with the shortwave
disturbances riding the ridge. These variations may impact the
timing of events over the next 24 hours or so, but forecast
confidence remains high for the coming storm system.

Look for today to start out with mostly clear skies and temperatures
near normal to a few degrees above normal. Strong diurnal heating
along and the ridge moving in from the west will warm temperatures
to five to ten degrees above normal by afternoon. Expect cu to pop
across the region this afternoon under the max heating and a
possible isolated shower over northeastern Utah, but the subsidence
will stifle most of the convection at least through mid afternoon.
Things change going into the evening with a shortwave disturbance
passing over the northern areas with isolated to scattered showers
in northeastern Utah and northwestern Colorado, spreading into the
Elkhead and Park mountains in the late evening, and spreading south
into the central Colorado mountains overnight. These showers look to
be light with little precip accumulation, but with an area of
divergence in the jetstream moving in overhead, these showers could
be stronger and more enduring like the showers we saw last night.

The ridge axis shifts east of the Divide this evening putting the
region under a southwesterly flow going into Saturday as the low
making landfall along the Oregon/Northern California Coast. As the
low moves inland, it splits into two shortwaves, the first taking
the high road through Utah and Colorado and the second taking the
low road, digging south along the Mexican Border a day or so behind
the first for an extended period of unsettled weather across the
region, but more on this below. With the approach of the first
shortwave trough Saturday afternoon, the pressure gradient
tightens over the region resulting in gusty southwest winds
Saturday afternoon common for Spring weather. Current forecast
is for gusts around 30 mph in the lower valleys and in the 40
mph range over the higher elevations. These speeds are below
headline values, but the winds will still be a nuisance. Clouds
will increase with a weak disturbance ahead of the trough that
will initiate showers in the Uinta Mountains Saturday afternoon
with moderate snow possible above 8,000 feet. Showers will
likely also develop over the rest of eastern Utah and Western
Colorado through the afternoon as deep AR moisture with IVTs
around 200 kg/m/s is pushed up from the southwest, and diurnal
heating warms the region to around ten degrees above normal for
one last day before the cooler air arrives. Again, these showers
will not produce significant precipitation until the main body
of this next storm arrives Saturday evening.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
Issued at 336 AM MDT Fri Mar 22 2024

Expect precipitation to increase in coverage and intensity Saturday
night as the long wave trough tracks eastward across across the
Great Basin. Models indicated the cold front driven ahead of the
trough will push eastward across the forecast area during the night
causing snow levels to fall to between 5500 and 6000 feet by sunrise
Sunday. Meanwhile, all the ingredients appeared to be present for a
widespread rain and snow event with convergence along the surface
front, strong mid-level upward forcing as indicated in Q derived
omega fields, and jet divergence in left exit of the 150+ jet to the
south indicated in model data. On Sunday, a lee side cyclone forms
over the eastern Colorado plains as the mid-level trough shifts east
of the Continental Divide. The cold pool at mid-levels will cause
lapse rates to steepen over the forecast area which, when combined
with wrap around moisture and more favorable westerly flow, will
keep rain and snow going over much of the area Sunday into Sunday
night. Continued cold air advection will cause snow levels to fall
further with model guidance suggesting a range from 4000 to 5000
feet from north to south. Latest model forecast snowfall totals from
Saturday night through 12Z/Mon ranged from 6 to 12 inches across the
western Colorado mountains, mainly above 8000 feet. At this point,
it appears Winter Weather Advisories may eventually be needed
but will hold off issuance with this package as the event
doesn`t begin to unfold until the 4th period so there`s still
time to better nail down timing and amounts.

Residual moisture in northwest flow, steep lapse rates, and
orographics will keep snow showers going over the Colorado mountains
Monday. Showers are expected to decrease Monday night as surface
cooling stabilizes the atmosphere, but scattered showers are likely
to persist, especially across the northern ranges. A mid-level
shortwave in the northwest flow moves across the area on Tuesday
causing showers to increase in coverage during the afternoon and
evening. On Wednesday, a transitory ridge forms over the area ahead
of the next eastern Pacific long wave trough. Some light showers may
linger along the Continental Divide, but most areas will see dry
weather. Models were in poor agreement by Thursday. The GFS
aggressively moves the Pacific trough across the forecast area
during the day. In contrast, the ECMWF only moves the trough to the
Great Basin while the Canadian maintains the ridge overhead. Model
blends/current forecast appeared to heavily favor the GFS solution
which points to the likelihood for precipitation. For those making
plans for later next week, be sure to check back because there is
little forecast confidence from Thursday and beyond.

Advection of colder air at the beginning of the long term period
will cause temperatures to drop significantly with highs on Sunday
expected to be around 20 degrees colder than those recorded
Thursday, or about 10 degrees below normal. Latest guidance
suggested little change can be expected through Tuesday. However,
with ridging and the onset of southwest flow Wednesday and Thursday
temperatures are expected to rebound to near normal levels.

&&

.AVIATION /12Z TAFS THROUGH 12Z SATURDAY/...
Issued at 510 AM MDT Fri Mar 22 2024

A northwesterly flow across the region is generating some low to
mid clouds through the northern and central mountains with brief
periods below ILS breakpoints at KASE and KRIL for the first
four to six hours of the TAF period. Additionally, low clouds
in the Eagle Valley are producing periods LIFR ceilings for the
next few hours. Otherwise, expect mostly VFR conditions and
light winds across the region through the TAF period, the
exception being a slight chance for showers in the vicinity of
KASE and KEGE after 06Z.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

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


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