250
FXUS65 KGJT 050540
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
1140 PM MDT Sat May 4 2024

.KEY MESSAGES...

- Very strong winds remain likely for much of eastern Utah and
  western Colorado tomorrow, with gusts upwards of 65 mph for
  the valleys and 80 mph for the mountains. Numerous wind
  highlights are in effect.

- A strong cold front will move through Sunday night into
  Monday, bringing widespread precipitation and the potential
  for several inches of accumulating snow to the mountains.

- Much cooler and unsettled weather will remain for the coming
  week, with several disturbances keeping mountain showers in
  the forecast most afternoons.

&&

.SHORT TERM /THROUGH SUNDAY NIGHT/...
Issued at 323 PM MDT Sat May 4 2024

As expected, a shortwave tracking along the southern border of
eastern Utah and western Colorado has provided some extra lift
and moisture to kick off some light showers over the southern
and central Colorado mountains. No lightning as of yet, but the
potential for a thunderstorm or two remains through this
evening. Elsewhere across the region, conditions have been
quiet, with mostly sunny skies and relative light southwest
winds. Change is on the horizon, however, as the much discussed
strong Pacific low has already moved into the Pacific Northwest
and the gradient ahead of it has already begun to tighten up.
The nose of this jet will be into western Utah late tonight, and
will be pushing into the Four Corners by sunrise tomorrow
morning. Between the increasing surface winds in advance of this
system and increasing cloud cover thanks to midlevel moisture
being advected in on the jet, tonight`s lows will be milder than
the last few nights, running around 10 degrees above normal.

All eyes turn to the much discussed winds tomorrow. The
approaching southwesterly jet is stacked from 700mb all the way
to 200mb, with speeds starting out at 50-60 knots and increasing
with altitude to 100 knots or more. Ensemble and climatological
guidance all agree that this is a rare event, with some of
these wind speeds above the 99th percentile for this time of
year, and with return intervals of one day in every 5-10 years,
depending on what source you look at. Winds are expected to
begin picking up after midnight tonight, with gusts of 50-60 mph
possible at the higher elevations of eastern Utah and far
western Colorado by 6AM. As the day progresses, strong diabatic
heating will promote deep mixing, tapping into those higher wind
speeds aloft, and bringing down gusts up to 60 mph in many of
the valleys, and up to 80 mph across the higher elevations. In
addition, virga showers will be possible in the afternoon as
moist midlevel air overrides very dry surface air, which will
lead to localized enhancement of already strong gusts. And on
top of that, downsloping off of terrain features such as the
Uncompahgre Plateau will locally enhance winds as well. With the
consistency and relative rarity of an event like this, have
opted to issue High Wind Warnings for eastern Utah and far
western Colorado, with Wind Advisories picking up as one moves
east. The highlights for the higher elevation zones kick in at
6AM, with the lower elevations joining in at 8AM. All highlights
run through midnight. The core of the jet moves in late
tomorrow afternoon and into the evening hours, with peak winds
expected between 3 PM and 9PM. Winds will gradually drop after 9
PM from west to east as the cold front pushes through and winds
weaken aloft.

Aside from the winds tomorrow, deep mixing will promote warming
through the day, although clouds and moisture will limit how
warm we can get. Highs are expected to top out near normal,
before rapidly crashing as the above-mentioned cold front moves
through Sunday evening into Monday morning. The frontal band is
progged to be on the doorstep around 6PM tomorrow afternoon.
Warm air ahead of the front will keep precipitation as mostly
rain, at least to start with, with higher elevations seeing a
rain/snow mix or all snow possible with post-frontal showers.
Little in the way of accumulations are expected with the
exception of mountains above 9000 feet. The southern mountains
will see a quick couple of inches, with the central and northern
mountains seeing amounts approaching advisory amounts. Will
leave it to the midnight crew to make a call on whether
highlights are warranted for these areas, as amounts continue to
drop from model run to model run.

Enjoy the sunshine today, and make sure to prepare for a big
change in the coming days. Take time to secure loose outdoor
objects if possible, and stay up to date with the latest changes
to this complex forecast.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
Issued at 323 PM MDT Sat May 4 2024

The main trough will be swinging through northeast Colorado and
the Front Range into the northern High Plains by Monday
afternoon with some lingering northwest flow behind it over our
northwest Colorado and central Colorado mountains. This will
allow high elevation snowfall to continue although rates are
expected to drop off quite a bit as the strongest forcing exits
the region. Showers may lessen mid day Monday before picking up
again Monday evening into Tuesday morning and potentially
continuing through much of the day Tuesday as an additional
shortwave moves across the north following the main trough.
Snowfall amounts with this second wave favor the Park Range and
to a lesser extent the Flattops with the better accumulations.
Through much of the week, we will stay in this unsettled flow
pattern as the broad low pressure trough remains anchored over
the Intermountain West and Northern Rockies as additional weak
shortwaves drop in from the north across our Continental Divide
mountains, resulting in a chance of showers over the northern
and central high terrain, but snow accumulations among the
higher peaks are expected to be limited with minimal impact.
Temperatures during this period will continue to remain cooler
than normal through at least mid week, by about 10 to 15 degrees
below climatology for early May. In fact, Tuesday night into
Wednesday morning may see the potential for more widespread
freezing temperatures, with some lower elevations like the Grand
Valley and Uncompahgre Basin being most susceptible due to
budding vegetation.

As this large trough exits to the east by Wednesday finally, we
will begin to warm up for the latter half of the week with
temperatures warming to 5 degrees below normal Thursday and
Friday and near normal by next weekend. There is some model
discrepancy though in the synoptic pattern as the GFS shows a
low dropping southward through the Great Basin by late in the
coming week and potentially closing off from the main flow,
leaving our CWA underneath a broad col or deformation region.
The ECMWF is much further west with this cut off low feature,
bringing it all the way out to northern California, with less
influence over the western slope. This cut off low shows signs
of becoming Rex Blocked, but it`s just a matter of how far west
and the positioning of these features is key to our sensible
weather and forecast. Still a ways out but much of the coming
week looks to be cooler than normal and unsettled for the most
part with a slow warm up towards the latter half of the work
week.

&&

.AVIATION /06Z TAFS THROUGH 06Z MONDAY/...
Issued at 1140 PM MDT Sat May 4 2024

Mid and high level clouds will continue to increase overnight
and through the day on Sunday out ahead of an approaching cold
front. Ahead of the front, very strong winds will develop out of
the south and southwest by mid-morning and continue through the
afternoon and evening. Sustained winds of 25 to 35 kts with
gusts of 40 to 50 kts will occur. A few showers may develop
across the higher terrain ahead of the front as well, but the
heaviest and most widespread precipitation will push through
along the front mainly after 00Z Sunday evening. As a result,
reductions in ceilings and visibility are likely Sunday night.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

CO...High Wind Warning from 8 AM Sunday to midnight MDT Sunday
     night for COZ001-006-011-020.
     Wind Advisory from 8 AM Sunday to midnight MDT Sunday night
     for COZ002-007-008-021-022.
     High Wind Warning from 6 AM Sunday to midnight MDT Sunday
     night for COZ003-017.
UT...High Wind Warning from 8 AM Sunday to midnight MDT Sunday
     night for UTZ022-024-027-029.
     High Wind Warning from 6 AM Sunday to midnight MDT Sunday
     night for UTZ025-028.
     Wind Advisory from 6 AM Sunday to midnight MDT Sunday night
     for UTZ023.

&&

$$

SHORT TERM...BGB
LONG TERM...MDA
AVIATION...TGJT