838
FXUS65 KGJT 261124
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
524 AM MDT Fri Apr 26 2024

.KEY MESSAGES...

- Isolated showers continue this morning with more widespread
  showers and thunderstorms expected again this afternoon.

- A potent system will move through the area Friday evening
  through Sunday morning bringing much cooler temps, valley rain
  and mountain snows to the region.

- Winter Weather Advisories remain in effect above 9000 feet for
  6 to 12 inches of snow. Advisories in UT begin at 6AM this
  morning while CO advisories begin at 6PM this evening, both
  continue through 6AM Sunday.

&&

.SHORT TERM /THROUGH SATURDAY/...
Issued at 154 AM MDT Fri Apr 26 2024

Light showers continued overnight as a weak wave moved across
the area. These showers will continue through the morning hours
though shortwave ridging is expected to limit coverage to a
degree. This all changes as we head into the afternoon, however,
thanks to an approaching trough and surface cold front. Like
yesterday, CAPE values will be on the order of 300 to 600 J/kg
across much of the CWA while lapse rates will be around 8C/km.
QG forcing is also showing a decent amount of lift across the
CWA so with all these ingredients in place, we can expect
another day with numerous showers and thunderstorms. Forecast
Skew-Ts continue to show an inverted V profile but not as deep
as yesterday though DCAPE values do reach 400 J/kg so some
stronger downbursts are certainly possible. Heading into the
high country, some snow will fall as the snow level will sit
around 9K feet. Of course, any stronger convection could drop
these snow levels noticeably. Either way, daytime heating will
limit any impacts to roadways as snow will melt there giving way
to some wet roads.

As the day progresses and the trough continues to approach the
CWA, a midlevel closed low will form just west of the Four
Corners region. Upper level support in the form of a 100-110kt
jet will be rounding the base of the trough Friday afternoon and
the wind speeds entering the trough will be just about equal to
those exiting the trough meaning the trough and front will be
slow moving. The end result will be a prolonged precip event
with banded precip setting up (where exactly is the tricky bit)
and accumulating mountain snows and precip for the valleys.
Precip will continue overnight Friday with accumulating
mountains snows for almost all of the higher terrain. Models
continue to paint 6 to 12 inches of snow so the Winter Weather
Advisories will remain in effect.

Precip continues Saturday across the CWA and with all the cloud
cover, precip and west through northwesterly flow, high temps
will be about 10 to 15 degrees below normal late April values.
By Saturday evening, the broad area of low pressure will be
more over eastern CO than the Western Slope but alas, precip
will continue.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
Issued at 154 AM MDT Fri Apr 26 2024

By Saturday evening, the low will have moved east of the Divide and
out onto the Plains of northeastern Colorado with wrap-around
moisture keeping orographic snow showers going overnight into Sunday
morning in the northern and central Colorado mountains. The
northwesterly flow aloft behind this system and lingering moisture
will support isolated to scattered showers in the mountains through
Sunday before tapering off in the evening. The Colorado mountains
above 9,000 feet can expect another two to four inches accumulation
from Saturday evening into Sunday evening. Since daytime
temperatures will stay around freezing Saturday under overcast skies
on Vail Pass and at the high elevations in general, the mountain
roads won`t have a chance to warm up through the day. Look for the
mountain roads to remain slick and messy overnight into Sunday even
though not much snow will fall overnight.

Models are in good agreement with a general longwave trough setting
up to the north across the western CONUS to the Great Lakes that
remains in place for the coming week. The zonal flow across eastern
Utah and Western Colorado will generally be dry with breezy westerly
winds each afternoon, but a series of shortwave systems moving
through the longwave to the north will brush the northern mountains
spawning isolated to scattered showers each afternoon in the
Elkhead, Park and Gore Mountains, and on the Flat Tops. Otherwise,
look for mostly clear skies and warm temperatures across the region
with most of the clouds that do form staying mostly over the
mountains each afternoon. Model agreement continues through the
week, but beyond Monday, wide dispersion shows up in the ensembles
that average out to the continued zonal pattern, but confidence is
very low on the solutions. This spells the possibility of one of the
shortwaves passing to the north digging deeper into the area to
possibly impact the central and even the southern mountains with
showers. The run-to-run consistency is is also not consistent; where
24 hours ago models were in agreement predicting H500 heights of 576
to 579 over the region which would spell very warm days by mid week,
the most recent runs are now showing these heights in the 570 to 573
range, much more moderate. We`ll just have to wait and see how this
one plays out.

&&

.AVIATION /12Z TAFS THROUGH 12Z SATURDAY/...
Issued at 519 AM MDT Fri Apr 26 2024

An approaching cold front will keep rainshowers in the picture
for today along with some thunderstorms in the afternoon.
Midlevel ceilings have spread across the region and will remain
through today. While VFR will be predominant, some brief MVFR
will be possible around the stronger cells. AFter 00Z, chancres
will increase for MVFR to occur more often. Some afternoon
thunderstorms are also possible so did include VCTS for many
sites to account for this possibility. ILS breakpoints will be
met early on for the mountain TAF sites with chances increasing
for other TAF sites to do the same later this afternoon.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

CO...Winter Weather Advisory from 6 PM this evening to 6 AM MDT
     Sunday for COZ004-009-010-012-013-018-019.

UT...Winter Weather Advisory until 6 AM MDT Sunday for UTZ023.

&&

$$

SHORT TERM...TGR
LONG TERM...DB
AVIATION...TGJT