665
FXUS65 KGJT 020530
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
1130 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 WEDNESDAY/...
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 /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 1130 PM MDT Wed May 1 2024

The last of the remaining showers primarily along the
Continental Divide mountains will continue to clear out to the
south and east over the next few hours. MVFR/ILS breakpoint
ceilings will hang on during that timeframe too before mostly
dissipating by sunrise. On Thursday, another disturbance will
brush across the northern tier of eastern Utah and western
Colorado. This will bring more clouds back into the picture,
especially north of I-70. Ceilings should mostly stay above ILS
breakpoints, however. Farther south, mostly sunny skies will
prevail. Winds will once again become breezy during the
afternoon hours with gusts of 25 to 35 mph common. Winds settled
down again not long after sunset.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

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