623
FXUS65 KGJT 052117
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
317 PM MDT Sun May 5 2024

.KEY MESSAGES...

- Very strong winds continue through this evening for much of
  eastern Utah and western Colorado today, with gusts up to 65
  mph for the valleys and 80 mph for the mountains.

- A strong spring storm is still on track to bring widespread
  precipitation tonight and Monday with significant mountain
  snow expected across the northern Colorado ranges. Light snow
  accumulations are possible for the higher valleys as well as
  most other mountain ranges by sunrise Monday.

- Much cooler and unsettled weather will be the rule for the
  rest of the week ahead as several disturbances keep mountain
  showers in the forecast most afternoons.

&&

.SHORT TERM /THROUGH MONDAY NIGHT/...
Issued at 317 PM MDT Sun May 5 2024

As expected, its been a bit windy across the Western Slope
today. Our anticipated upper level trough and associated strong
cold front continues to approach from the west this afternoon,
leading to an ever-tightening southwest gradient overhead.
Surface gusts have consistently been in the 45 to 55 mph range
with some of the higher elevations gusting in the 65 to 75 mph
range. This has been the standard for more than two-thirds of
the forecast area with several locations having already hit
their high wind criteria today, most notably in the northern
zones. These strong winds in the warm sector of the upcoming
trough have allowed temperatures to climb several degrees above
the norm for early May, though the rapid uptick in clouds has
slowed the warming in the last hour or so.

Suffice to say, today has been the quintessential sign that big
changes are on the way. The cold front is still on track to be
right on our doorstep around sunset before quickly pushing
southeast across northeast Utah and northwest Colorado tonight.
Showers will continue to spread from west to east in response,
remaining high-based at first with some more of those pesky
winds before the profile gradually saturates. Plenty of forcing
associated with this system as the base of the low swings
through by mid to late Monday morning. That means conditions
could rapidly deteriorate, especially in the high country. As
noted previously, rates around an inch per hour cannot be ruled
out with snow levels quickly dropping to the 8-9kft mark with
the front. Even though winds will weaken once the front passes,
when it comes to travel impacts it will barely be noticeable
with continued strong winds of 40 to 50 mph in the mountains.
Therefore, went ahead and expanded the Winter Weather Advisories
to include zones 10, where a quick 3 to 6 inches of snow will
fall at those higher sites tonight under those blustery
conditions. Borderline criteria remains in the remaining
southern and central Colorado mountains but with this quick
system confidence is not high enough on the impacts being in
more than half of the zone.

Monday`s forecast remains on track as wraparound moisture
impacts the region. Instability in the wake of the front paired
with orographics will keep showers and perhaps some embedded
storms along the Divide. Denser cloud cover and showers will
begin to dissipate elsewhere. The much colder airmass will drop
Monday`s highs back down to well below normal. On Monday night
another piece of energy wrapped around the larger upper level
trough will drag across the northern tier of the forecast area.
This will see at least scattered showers occur Monday night and
into Tuesday morning.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
Issued at 317 PM MDT Sun May 5 2024

Large scale troughing will dominate the western half of the country
by Tuesday, with westerly to northwesterly flow in control over
eastern Utah and western Colorado. Moisture wrapping around the low
pressure center in the Northern Plains will combine with some subtle
waves in the flow aloft to bring rain and snow showers across the
higher elevations of northeast Utah and northwest Colorado. This
moisture will be modest, but decent dynamic lift with the passing
wave and favorable orographics will bring generally 2-4 inches of
snow to elevations above 8500-9000 feet in the Flat Tops, Park, and
Elkhead ranges. More substantial accumulations are possible in the
Park Range above 9500 feet, and the need for a Winter Weather
Advisory cannot be ruled out just yet. Outside of these areas,
however, Tuesday will be generally dry and on the breezy side. A
reinforcing shot of cold air will accompany a largely dry cold
frontal passage early on Wednesday, although a few light showers at
the higher elevations cannot be completely ruled out. Winds will
relax in the wake of this front as the jet core aloft moves east and
the entire jet stream sags south of the Four Corners. This also
means some very cold morning lows are possible Wednesday morning.
Current guidance now has a low of 32F in Grand Junction which, if it
verifies, would break the previous record of 33F for that date, set
in 1979. In addition, large portions of the forecast area are
looking at lows in the 20s and low 30s for Wednesday and Thursday
mornings. This could be a problem for agricultural interests as the
growing season is well and truly underway at this point. Be sure to
stay tuned to the forecast over the next several days, because the
potential need for freeze highlights is increasing.

The pattern gets much more complex from Wednesday onward, making the
forecast difficult to pin down. Ensemble and deterministic model
guidance are starting to come around to a solution where the center
of low pressure in the northern plains begins to elongate and
retrograde west into the southern Great Basin. At the same time,
high pressure begins to build into the Pacific Northwest, setting up
a Rex Block over the western half of the country. There`s suggestion
of this elongated area of low pressure spinning off its own cutoff
low over southern Nevada and northern Arizona, with eastern Utah and
western Colorado coming under weak southerly flow. This would advect
some warmer air into the region which, in addition to the general
moderating of the cold airmass aloft, would account for the gradual
warming trend during the late week period. It`s unclear how much
moisture this area of low pressure would be able to tap into, but
even some modest moisture would be enough to keep those pesky
afternoon mountain showers in the forecast through the end of the
week. Blocky patterns like these tend to stick around for a while,
and models typically have difficulties in such scenarios. A large
amount of uncertainty remains for the end of the long term period,
as models are all over the place over when the cutoff low finally
gets kicked back into the westerly flow and dragged out of the
Desert Southwest, and what exactly that means for us here in eastern
Utah and western Colorado.

Temperatures will remain near to much below normal through the
period, warming up to near normal values by late week. Tuesday and
Wednesday will see high temperatures running generally 5-10 degrees
below normal, with highs almost 20 degrees below normal across
northeast Utah and northwest Colorado. Lows on Wednesday and
Thursday mornings are set to run 5-10 degrees below normal before
also moderating by the end of the week.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1130 AM MDT Sun May 5 2024

Mid and high level clouds continue to pass overhead at this
hour. Winds have already begun gusting 30-40 knots out of the
southwest at may terminals across the area. Gusts up to 50
knots are not out of the question today, with sustained winds in
the 30-40 knot range. A few light showers may develop over the
higher terrain this afternoon ahead of the cold front, and may
bring some light precipitation, but more likely will produce
enhanced wind gusts. A strong cold front pushes through from
west to east this evening, with rain and snow possible, as well
as reductions to visibility and ceilings. VFR conditions will
prevail through 00z this evening, with deteriorating conditions
after.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

CO...High Wind Warning until midnight MDT tonight for COZ001-003-
     006-011-017-020.
     Wind Advisory until midnight MDT tonight for COZ002-007-008-
     021-022.
     Winter Weather Advisory from 6 PM this evening to 6 PM MDT
     Monday for COZ004-010-013.
UT...High Wind Warning until midnight MDT tonight for UTZ022-024-
     025-027>029.
     Wind Advisory until midnight MDT tonight for UTZ023.

&&

$$

SHORT TERM...MMS
LONG TERM...BGB
AVIATION...TGJT