-- Discussion containing changed information from previous version are highlighted. --
727
FXUS65 KGJT 032345
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
545 PM MDT Fri May 3 2024

.KEY MESSAGES...

- A system will brush the northern tier of eastern Utah and
  western Colorado today, bringing a few valley rain and
  mountain snow showers through this evening. Minor
  accumulations are expected with little to no impacts.

- Scattered showers and isolated thunderstorms are possible
  late Saturday mainly in the mountains. Elsewhere expect warmer
  and dry conditions.

- A strong system is expected on Sunday and Monday. It will
  bring widespread precipitation and strong winds. A High Wind
  Watch has been issued for much of eastern Utah and far western
  Colorado Sunday morning through Sunday evening.

&&

.SHORT TERM /THROUGH SATURDAY NIGHT/...
Issued at 348 PM MDT Fri May 3 2024

The cold front and upper level jet associated with the shortwave
trough moving across the north is evident both on satellite and
radar across the eastern Tavaputs in northeast Utah into
northwest Colorado across the Flattops and into the northern
Park Range. Some light showers are occurring in Craig and Hayden
with rain at Hayden and rain flipping over to snow at Craig.
Roads remain wet to dry according to webcams in that neck of the
woods with trace accumulations on the grassy surfaces north of
Craig where it`s actively snowing. All in all, impacts remain
minimal with maybe 2 to 5 inches of snow at the higher
elevations of the Park Range but other than that, roads are
expected to remain wet. Much different story along and south of
I-70 where dry conditions are evident as relative humidity is
in the teens with winds gusting in the 30s and 40s. Some locally
higher gusts are occurring due to presence of virga showers but
these gusty winds combined with the low relative humidities is
leading to critical fire weather conditions at times.
Temperatures today along and south of I-70 are sitting at 4 to 8
degrees above normal with areas north of I-70 cooler at 5 to 10
degrees below normal.

Showers should come to an end early this evening as this
shortwave over the north exits and the jet and cold front lift
northward as a warm front by Saturday. Strong WAA is expected to
take place Saturday afternoon with high temperatures warming by
about 5 degrees along and south of I-70 with a warm up of 10 to
15 degrees from today across the north. Highs on Saturday will
be 5 to 10 degrees above normal across most of the area. In this
southwest flow, we will still see some breezy conditions, but
winds are expected to be less than today as the jet lifts north
and shortwave ridging takes place. The hi-res CAMs are
indicating a bit of instability Saturday afternoon with a weak
shortwave moving through the southwest flow, skirting the
divide, so isolated to scattered thunderstorms are possible
along the western Colorado mountains mainly along the divide.
The gradient tightens Saturday night into Sunday ahead of a
strong closed low that will dive southeastward from the PacNW
into the Great Basin, settling over Nevada by Sunday morning.
More on this in the Long Term discussion below.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
Issued at 348 PM MDT Fri May 3 2024

By Sunday morning, eastern Utah and western Colorado are
expected to be sandwiched between a ridge over the Great Plains
and a strong Pacific Low dropping into the Great Basin. Wrapping
around the base of this low, an intense southwesterly jet is
expected to push into the region on Sunday. Strong winds are
expected throughout the column, with 45-60 knots at 700mb and
95-110 knots at 250 mb. 700 mb is roughly the same altitude as
some of the highest peaks in eastern Utah and western Colorado,
so at a baseline, without factoring in any other daytime
boundary layer mixing or virga shower enhancement, mountain
locations are looking at least 50-60 mph gusts on Sunday
afternoon, with valley locations looking at a baseline of at
least 35-45 mph. But of course, we do have to account for those
other factors, with strong diabatic heating allowing for deep
boundary layer mixing to tap into and bring down the much higher
windspeeds aloft, and virga showers breaking out ahead of the
approaching cold front. With all these other factors accounted
for, another 10-20 mph added onto the baseline makes a
reasonable forecast, and is bared out by probabilistic guidance
indicating a high probability (>99%) of gusts 45-55 mph in the
valleys and 55-65 mph for the mountain regions. Peak gusts into
the 60s across the lower elevations and into the 80s at higher
elevations will also be possible especially across eastern Utah
and far western Colorado zones. Eastern Utah will likely see
some of the highest gusts as the jet remains overhead here the
longest, providing ample time for deep mixing to tap into the
jet and mix down stronger gusts through the day. A High Wind
Watch has been issued for all valleys and most mountain areas of
eastern Utah, as well as the lower valleys and mountains of far
western Colorado where potential and confidence is highest for
gusts 55 to 65 mph in those valley zones and gusts to 75 mph in
those mountain areas. The High Wind Watch will begin 8 AM Sunday
and last through 10 PM. Stay tuned for updates relating to this
situation, and if you have outdoor furniture or other objects
prone to being disturbed by strong, gusty winds, take the time
now to prepare.

The strong winds are just the first part of the impacts from
this approaching Pacific low. An potent cold front is progged to
move through late Sunday into early Monday morning, with
substantially colder air moving in behind it. 700mb temperatures
on Sunday morning are currently forecast around 4C, and within
24 hours are forecast to drop to nearly -7C. In reflection of
this, snow levels will start out on Sunday morning at 9500-10000
feet, and will crash down to 5500-6000 feet by the same time on
Monday. Only the highest elevations will see snow for the
duration of this system, with most everywhere else beginning
with rain showers on Sunday evening. Higher elevation valleys
and lower slopes of the mountains will see a changeover to snow
as the cold front passes. Current guidance doesn`t keep much
precipitation around in the post-frontal airmass, with the
exception of orographic showers across the northern mountains,
so little if any accumulating snow is expected for most
locations. The northern and central mountains remain most
favored to see the highest QPF, with totals 0.50" to 1.00" still
in the forecast from Sunday morning through Monday night. The
southern mountains may see 0.25" to 0.50" total through the same
period, while the lower elevations can expect 0.25" or less.
Most locations will see this all or mostly in the form of rain,
although the central and especially northern Colorado mountains
above 9000 feet will see a substantial chunk of that QPF in the
form of several inches of snow. Travel over mountain passes may
be a bit messy on Monday morning.

Cold and unsettled northwest flow sets up in the wake of this
low, which is forecast to eject into the northern Plains Monday
evening. Some wrap around moisture from this low combined with
favorable flow will keep light orographic showers going over the
northern mountains. General troughiness is expected to linger
from Tuesday on through the end of the week, with multiple waves
riding the northwesterly to westerly flow over eastern Utah and
western Colorado and keeping mountain showers a possibility
most afternoons. The cooler air that moves in with the cold
front late Sunday into Monday will remain in place through the
late week period, with temperatures running 5-10 degrees below
normal. That means highs in the 50s to low 60s across the lower
elevations, with 30s-40s up high, until Friday when the blended
guidance indicates temperatures warming to near normal values.

&&

.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
-- Changed Discussion --
Issued at 540 PM MDT Fri May 3 2024

Gusty southwesterly winds continue at this hour but will be
dying down over the next few hours and by 03Z, gusts should be
over. As far as ceilings and visibilities are concerned, a cold
front is bringing some precip and clouds to KHDN, KASE, and KEGE
though only KHDN is MVFR at the moment due to some snow. Having
said that, conditions should improve for those areas as well
over the next few hours. Overnight, mostly clear to clear skies
expected with light winds. Tomorrow, few to scattered skies on
tap with lighter winds.
-- End Changed Discussion --

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

CO...High Wind Watch from Sunday morning through Sunday evening for
     COZ001>003-006-011-017-020-021.
UT...High Wind Watch from Sunday morning through Sunday evening for
     UTZ022-024-025-027>029.

&&

$$

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