835
FXUS65 KGJT 300525
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
1125 PM MDT Mon Apr 29 2024

.KEY MESSAGES...

- A disturbance passing to our north will bring rain showers and
  mountain snow to the northern half of the CWA tonight. Snow
  accumulations of 1-3 inches are possible.

- Afternoon winds will remain gusty this week, as a series of
  disturbances along the jet stream impact the region.

- A brief cool spell on Thursday in the wake of a cold front
  will drop temperatures, before things warm back up heading
  into the weekend.

&&

.SHORT TERM /THROUGH TUESDAY NIGHT/...
Issued at 347 PM MDT Mon Apr 29 2024

Satellite imagery shows the models are tracking well with the
low descending out of the Gulf of Alaska off the coast of
British Columbia into the Pacific Northwest, a weak longwave
trough across the western CONUS to the Great Lakes producing a
zonal flow across eastern Utah and Western Colorado, and the
last low pressure system that pass through the region Saturday
exiting stage right up over the Great Lakes into Canada. Our
weather will be impacted through this week by disturbances
passing to the north in the longwave pattern bringing continued
unsettled weather to the areas generally north of the I-70
corridor. Currently the westerly flow is driving the residual
moisture in the region onto the terrain producing scattered
light orographic showers along and north of I-70, and isolated
showers to the south. Guidance hasn`t picked up on the
orographic effects and had to pencil in PoPs to cover the
northern areas. Warm air advection aloft has capped these
showers below about 500mb, and with the plentiful residual
moisture in the area generating significant cloud cover
preventing diurnal heating, stronger showers or storms are
unlikely to develop this afternoon.

A shortwave passes to the north this evening into Tuesday
morning bringing showers and an isolated thunderstorm across the
northern areas with some snow accumulation possible above 9,000
feet. Expect up to an inch snow accumulation possible in the
eastern Uintas, and a few inches possible on the Flat Tops, and
on the Park, Elkhead and Gore Ranges. Behind this disturbance, a
band of drier air pushes into the area by afternoon to clear
out the skies and heat the surface temperatures to near normal
or a little above normal that will increase mixing the winds
aloft down to the surface. Look for westerly winds across the
region tomorrow afternoon around 20-25 mph gusting 30 to 35 mph
with the stronger winds across the northern two thirds of the
region. As a second shortwave digs deeper into Idaho and Wyoming
overnight Tuesday, winds aloft increase to near 70 kts at H500
across the northern areas and more like 40 kts across the
southern areas with the tightening pressure gradient. Would not
be surprised to see a few strong overnight gusts lee of higher
terrain, but again, none of the guidance seems to pick up on it.
This is something to watch in the short term. Otherwise, look
for a few isolated light showers overnight in the northern
mountains going into Wednesday morning.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
Issued at 347 PM MDT Mon Apr 29 2024

The pattern remains progressive Wednesday as the positive tilt
mid- level trough shifts eastward over the Great Basin during
the day. Models drive the cold front associated with this system
east- southeastward across the northern half of the forecast
area before the days out, and the boundary may drift farther
south than earlier runs had indicated. Moisture running
northeastward ahead of the system combined with surface
convergence, good dynamic forcing at the mid and jet levels will
lead to numerous showers and embedded thunderstorms by
Wednesday afternoon with the northern Colorado mountains
favored, though chances are good for the eastern Uinta
Mountains, the northwest Colorado plateau and the central
Colorado mountains as well. Areas to the south will see little
to no chance for precipitation. Cooler temperatures appeared
reasonable for Wednesday, especially for the northern and
central zones with frontal passage. That said, not confident
models are cooling it enough for areas along and north of the
I-70 corridor, so replaced NBM with bias corrected ConsAll which
appeared more reasonable and has shown better verification
numbers.

The trough axis moves to just east of the Continental Divide by
12Z/Thu while the cold front is driven to the southern CO/UT
borders. The evening period will remain active for the
previously mentioned locations with coverage decreasing late
Wednesday night. Twenty-four hour snow accumulations approach
advisory levels for the Park Range, but only for areas above the
treeline, so will not issue highlights for this event unless
later runs warrant reconsideration. NBM seemed a bit out of step
with latest operational runs on Thursday which only indicated
slight to low chance PoPs over the Elkhead and Park with little
chance elsewhere. In contrast, NBM holds onto to middling chance
PoPs over the northern and central Colorado mountains and
adjacent valleys throughout the day. Check back tomorrow and I`m
certain we`ll be looking at markedly reduced chances for
additional showers on Thursday. What is more certain however, is
that temperatures will dip by around 10 degrees for the entire
forecast area, or around 5 to 10 degrees below normal.

Another fast moving system impacts the north on Friday bringing
another round of rain, snow and embedded thunderstorms for the
northern and central Colorado mountains and, to a lesser extent,
their adjacent valleys. This system moves out quickly with
conditions improving Friday night. The weekend outlook appears
pretty favorable for those looking to get out and recreate. A
transitory ridge moves overhead on Saturday as a low deepens
over the West, then shifts east on Sunday as the western low
begins its approach. Models not in good agreement with the
positioning of the low center, but this doesn`t appear to be a
factor for our weather until early next week. Consequently,
aside from some isolated moist convection over the Continental
Divide, dry and warm weather is expected with the lower valleys
climbing into the 80s with 70s in the higher valleys and upper
50s and 60s in the mountains.

&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 1124 PM MDT Mon Apr 29 2024

A mid level cloud deck with isolated to widely scattered showers
is moving across northern portions of Utah and Colorado tonight.
ILS cigs may be met at times under this light precipitation but
impacts of MVFR or below are not forecast at this time. Winds
will increase aloft which will create areas of LLWS as this
system works through with some of this wind making to the ground
as gusts over 25 mph tomorrow afternoon.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

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