199
FXUS65 KGJT 012101
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
301 PM MDT Wed May 1 2024

.KEY MESSAGES...

- A cold front will cool temperatures 5-10 degrees across much
  of the region Thursday.

- Valley rains and mountain snow this afternoon will move east
  of the Divide by midnight. 1-2 inches of snow is expected
  above 9000 feet, with some higher peaks getting more.

- Scattered showers and thunderstorms will be capable of
  producing small hail, lightning and gusty winds this afternoon
  and early evening.

- Warm and dry conditions return for the weekend ahead of more
  unsettled weather early next week.

&&

.SHORT TERM /THROUGH THURSDAY NIGHT/...
Issued at 256 PM MDT Wed May 1 2024

The persistent low pressure system centered along the Canadian
Border about the Alberta-Saskatchewan-Montana triple point continues
to dominate the weather pattern keeping the longwave trough in place
across the Western CONUS. A stronger shortwave and cold front is
moving under the low supported by a 100kt jet aloft. This shortwave
looks to be enough to finally eject the low to the east by Thursday
evening, bringing changes to our weather in the next week. The tight
northerly pressure gradient at H500 is producing 60kt zonal winds
aloft across eastern Utah and Western Colorado. A band of showers is
tracking northwest to southeast across the region associated with
the right entrance region of the jet. With the dry inverted-V
sounding from this morning, little of the precip is reaching the
ground, but the showers/virga is effectively mixing the strong
westerly winds to the ground with 30 to 45 mph gusts have been
reported across the northern and central portions of the region.
These showers will continue to push through to the southeast across
the region in sync with the right entrance region of the jet, moving
east of the Divide by late this evening. The actual cold front with
this system will start into the region in the Uintas late this
afternoon, working its way to the southeast through the evening
hours before stalling out on the San Juans in the overnight. Look
for the morning low temperatures 10 to 15 degrees cooler tomorrow
than this morning in the areas north of the San Juan Mountains.

The skies clear out overnight with sunny dry weather on tap for at
least the morning. By noon we`ll start seeing some mid to high
clouds moving down from the northwest ahead of the next shortwave
trough due into the region Friday morning. The clouds will generally
stay to the north of the I-70 corridor, and though the sun will feel
warm south of I-70, temperatures will remain about five degrees
below normal through the day behind the frontal boundary. There is a
very slight chance for showers to initiate over the northern
mountains overnight Thursday, but these will likely hold of until
the morning. With the strong zonal flow aloft continuing over the
region, look for more gusty west winds again tomorrow afternoon.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
Issued at 256 PM MDT Wed May 1 2024

The progressive pattern will continue to impact eastern Utah and
western Colorado through the long term period. Due to the polar
jet`s seasonal migration north, showers will continue to miss the
lower elevations of the Four corners region.

That said, the next mid-level trough in the series begins to impact
the area early Friday morning and will continue to generate showers
through the afternoon according to model consensus. The lifting
mechanism initially is produced from overrunning and jet divergence,
but transitions to vorticity advection and orographics as the trough
passes over the north during the day. Accumulations across the
Elkhead, Park, Flat Top and eastern Uinta mountains are expected to
be light, generally from 1 to 3 inches above 8500 feet with locally
higher amounts. Timing of the cold front associated with this wave
is expected to allow temperatures to rise a couple of degrees north
of the I-70 corridor and around 5 degrees to the south.

Subsidence on the backside of the trough with a transitory ridge
building over the area ahead of a closed low off the coast of the
Pacific Northwest will result in a break in the weather Friday
night. On Saturday, the low to the west moves ashore over southern
Oregon causing the area to fall under broad difluent southwest flow
aloft. Meanwhile, strengthening southwesterlies will drive the cold
front northward and out of the forecast area with much warmer air
filtering into the region during the day. Lingering moisture is
expected to yield isolated to scattered showers and thunderstorms
over the mountains of the Continental Divide Saturday afternoon
while the remainder of the region remains dry and warmer with highs
climbing to around 10 degrees above normal.

From Saturday night to Sunday the closed low moves over the Great
Basin. Pre-frontal height packing ahead of the impressive cold front
associated with this system will result in windy conditions from
late morning Sunday into the early evening. Moisture arrives over
northeast Utah early with showers becoming likely for the eastern
Uinta Mountains during the afternoon with more scattered activity
north of the I-70 corridor and far northwest Colorado. 12Z
operational models were in better agreement and all indicated the
low will pass over the area Sunday night driving it`s cold front
eastward to the High Plains by 12Z Monday. Consequently, this will
be the most active phase of the storm and snow levels will be
lowering to between 6 and 7 Kft. The moisture wrapped system is
expected to continue to generate showers over the northern and
central Colorado mountains and northwest plateau on Monday. Snowfall
accumulations from this system have the potential of reaching
advisory levels across the Flat Tops and the Elkhead and Park
Ranges. Temperatures cool a bit in the warm sector of the storm on
Sunday due to clouds and virga/showers, but should still run 5 to 10
degrees above normal while overnight lows will considerably milder
than normal due to mixing associated with frontal passage. However,
on Monday highs are expected to fall by 5 to 10 degrees below normal
as the colder air takes hold of the region.

A secondary mid-level short wave trough sweeps over the area Monday
night into Tuesday and as a result, the chance for showers over the
northern mountains and northwest Colorado plateau will continue. Any
additional accumulations will be light as it stands now. Overnight
lows Tuesday morning will be colder, but at this time it doesn`t
appear they will approach freezing for areas with sensitive
vegetation. Highs moderate a few degrees but will continue to run
just a little below seasonal norms.

&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 1159 AM MDT Wed May 1 2024

A line of rain showers extended from KHDN to KCNY with a broader
shield of showers south of KRIL extending northeast over KEGE at
17Z. This activity was tracking slowly eastward at roughly 10 to
15 mph. Consequently, showers over KHDN will be coming to end in
the near term while chances will be rising for KEGE, KRIL, KEGE
and KASE early this afternoon. This activity has a high
likelihood of lowering ceilings below ILS breakpoints for KRIL,
KEGE and KASE, but there`s a lesser chance that this activity
will bring the flight category below VFR. Chances for showers
are fairly low to the south so did not mention more than VCSH.
The same can be said for KVEL and KCNY. Showers become more
likely for KEGE and KASE from late afternoon through the evening
as the latest system continues to push eastward over the area.
Strong and gusty winds from the west and northwest continue into
the evening, at times enhanced by showers. Conditions improve
later tonight.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

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