NWS Grand Junction, CO wrote its last area forecast discussion before the first event at Feb 25, 9:46 PM MST, 1 hour 14 minutes earlier. Its key messages:
Area forecast discussion, Feb 25, 9:46 PM MST, 1 hour 14 minutes before
Area Forecast Discussion
National Weather Service Grand Junction CO
946 PM MST Sun Feb 25 2024
.KEY MESSAGES...
- Warm temperatures continue through tomorrow before a cold
front drops temperature near to below normal for a few days.
- Precipitation with the next winter storm begins for the
southern and central mountains tonight and spreads north
through the day tomorrow, numerous highlights in effect.
- Strong southwesterly winds will impact the region late
tomorrow through Tuesday, with valleys gusting 40-50 mph and
mountains in excess of 60 mph.
&&
.SHORT TERM /THROUGH TUESDAY/...
Issued at 324 PM MST Sun Feb 25 2024
Conditions remain sunny and mild across eastern Utah and western
Colorado today, with temperatures running a good 5-10 degrees above
normal. Low amplitude ridging remains in control, keeping things
quiet for now. A cutoff low remains spinning off the coast of
California, while a northern stream trough is just now dropping into
British Columbia. Flow around the cutoff low is pumping deep AR
moisture into the Desert Southwest, with water vapor imagery
indicating the northern edge of the plume is just south of the Four
Corners. This is also evident by the increasing high cloud cover
over that area. These are the three key features of note that will
have influence over our weather for the next few days. As the
northern stream trough moves through the Pacific Northwest, the
cutoff low will drift eastward, turning flow aloft from westerly to
more southwesterly and directing the associated jet and AR plume
into eastern Utah and western Colorado late tonight. Clouds will be
on the increase, and snow showers are expected to break out over the
San Juans and the Elks and West Elks after midnight, with south
facing slopes most favored. Additionally, the pressure gradient
aloft begins to tighten up tonight as the northern and southern
stream jets combine overhead, leading to increasing gusts beginning
at the highest elevations. By 6AM tomorrow morning, gusts over the
San Juans will be 40-50 knots, which, when combined with the
snowfall, will lead to blowing snow and reduced visbilities. The
afternoon will bring a brief lull in activity as forcing switches
from a weak shortwave and orographics to the much stronger northern
stream trough, which not only has some potent dynamic forcing, but
will also be pulling a strong cold front along with it.
Precipitation will kick back in in earnest tomorrow evening, along
with very strong winds. The highest elevations could see gusts in
excess of 70 mph tomorrow night, while lower valleys could see gusts
of 35-45 mph. The cold front will also begin working into northeast
Utah and northwest Colorado tomorrow night, bringing increased
chances of banded precipitation and snow squalls.
Pacing out the winter highlights with this system was a bit tricky.
Two waves bringing accumulating snow, separated by a roughly 6 hour
break, as well as very strong upper level winds mixing down to the
surface throughout the duration, all had to be factored in. The San
Juans are the only range to really see this downturn in activity
tomorrow afternoon, and as such start out with Winter Weather
Advisories tonight, a break after 11AM tomorrow, and then Winter
Storm Warnings from 5PM tomorrow through 11PM Tuesday night. While
the Southern San Juans will see advisory level snow with this first
wave, the Northern San Juans may not. However, the Northern San
Juans will see wind gusts in excess of 60 mph, which is enough to
make even an inch of fresh snow into an impactful amount, and
therefore to be included in the Advisory. The Winter Storm Warning
for the Elks and West Elks also goes into effect at 11PM tonight,
and runs for the duration of the event. This area is currently
forecast to see the highest accumulations, the highest wind gusts,
and very little in the way of a break to justify breaking the
highlights into shorter segments. The northern mountians and the
Gore Range join in at 6AM tomorrow morning, as snow begins to spread
northward ahead of the approaching northern stream trough. As colder
air works in as well, snow over the Uncompahgre Plateau and Grand
Mesa picks up tomorrow night, and as such their warning kicks in at
5PM. All highlights run through 11PM Tuesday night. Storm totals for
all ranges are in the 1 to 2 feet range, although amounts in excess
of 3 feet are possible on favored slopes.
Precipitation over the lower elevations will be rain, at least to
begin with. A transition to snow may occur tomorrow night,
especially across northeast Utah and northwest Colorado as
temperatures cool overnight and the cold front brings in even colder
air. Additional highlights may be needed for this area, as well as
for the Utah mountains, but as these highlights would be for Tuesday
onward, will leave the final decision to the night crew. Wind
advisories for the lower elevations may also be needed tomorrow night
into Tuesday, as those strong upper level winds work down to the
surface all across the CWA. Current guidance has sustained winds of
20-30 mph, with gusts up to 45 mph, for valley locations late
tomorrow evening, which puts them in borderline Wind Advisory
criteria. An extra model run might be just what's needed to push the
decision in either direction, so will leave this for the midnight
crew as well.
Wrapping it all together, enjoy the nice weather today. The Western
Slope is about to go from sunny and mild to wet and wild in a
hurry.
&&
.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
Issued at 324 PM MST Sun Feb 25 2024
The cold front will be on our doorstep daybreak Tuesday morning
before quickly pushing through our northern and central zones by
midday. Tuesday afternoon will see the front push south as the base
of the trough reaches the Four Corners region. A continued strong
gradient out ahead of the front will produce 250mb winds of 140 to
170 kts underneath the jetstreak, resulting in blustery conditions
at the surface. Winds across the northern tier of the forecast area
will exceed 15 to 20 mph sustained with gusts of at least 30 mph
Tuesday. Even stronger winds are anticipated south of the I-70
corridor into the Tuesday evening hours with sustained winds of 25
to 35 mph and gusts of 40 to 50 mph in the lower elevations. The
high country, particularly across the San Juans, Elk and West Elk
ranges, will have gusts of 50 to 60 mph. The higher peaks (above
pass level) have a 60 to 80 percent chance for wind gusts of 70 mph
or greater. Needless to say, these strong winds will be responsible
for blowing and drifting snow, likely reducing visibilities to a
quarter mile or less at times, reinforcing the decision to opt for
Winter Storm Warnings rather than advisories with this system. As
noted above, wind advisories may be needed in some of the lower
elevations, particularly across the Four Corners which remain firmly
under the jetstreak Tuesday afternoon.
Widespread precipitation will continue throughout the day on Tuesday
before activity tapers off Tuesday evening and night once the front
exits the region. Plenty of orographic support and AR moisture will
keep snow going in the mountains with moderate to heavy rates
expected along the Divide. Warm air out ahead of this system will
complicate snow levels for the mid and lower valleys but, overall,
confidence is high the northern and higher valleys along the I-70
corridor at least will have transitioned over to snow by Tuesday
morning. Forcing provided by the front paired with the strong winds
and abundant moisture will lead to a couple to more than several
inches of snow in the Lower and Central Yampa River Basins as well
as the Central Colorado River Basin by mid Tuesday afternoon. We'll
have to wait and see how much of an impact this will have on the
roads given the aforementioned warm antecedent conditions but, all
the same, a place to monitor for future highlights. Another thing to
consider...those pesky snow squalls. Strong frontogenesis and
indications of banding in the CAM guidance leads to increased
concerns for snow squalls Tuesday morning and afternoon. This is
strongly reflected in the almost maxed out snow squall parameter
along the front on Tuesday. The main theme from both this and all
previous forecast packages remains the same...please stay tuned to
the latest forecast and road conditions before travelling early this
week, and consider altering travel plans if possible.
Subsident dry air settles overhead Tuesday night and into Wednesday
under cooler northwest flow. Flow quickly shifts to the west by
Wednesday night. This will see high clouds gradually increase on
Thursday as the next bowling ball of a closed low intensifies over
the Gulf of Alaska. Strong southwest flow will return to the Desert
Southwest in response with the gradient rapidly tightening as we
head into the weekend due to the slow push inland of the trough
upstream. Blended guidance is quick to bring showers into northeast
Utah and northwest Colorado Saturday morning and afternoon, but for
now thinking precipitation will hold off until the latter half of the
weekend. One thing is for sure. Our period of unseasonably cool
weather early to mid week will be short-lived as warm air advection
will see temperatures rebound back to several degrees above normal
from Thursday onwards.
&&
.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 946 PM MST Sun Feb 25 2024
High clouds will continue to stream across the south and
central areas overnight, expanding northward by the morning
hours. LLWS is possible among many locations as stronger winds
increase aloft. Light snow is expected along the higher terrain
of the divide during the overnight and morning hours. CIGS will
lower for the mountain sites during the morning with ILS
breakpoints being reached by the afternoon. Strong winds will
eventually mix to the surface at all sites by late morning into
the afternoon hours with gusts 30 to 40 kts possible at times.
While KTEX and KASE stand the best chance of seeing
prevailing showers during the day, other TAF sites near the
divide like KHDN, KEGE and KGUC have a better chance of seeing
showers after 00Z or by Monday evening. More widespread
precipitation is expected beyond 06Z Tuesday with deteriorating
conditions as a strong cold front moves through the region, but
that is beyond this current TAF period.
&&
.GJT WATCHES/WARNINGS/ADVISORIES...
CO...Winter Storm Warning from 6 AM Monday to 11 PM MST Tuesday for
COZ004-010-013.
Winter Storm Warning from 5 PM Monday to 11 PM MST Tuesday for
COZ009-017>019.
Winter Storm Warning until 11 PM MST Tuesday for COZ012.
Winter Weather Advisory until 11 AM MST Monday for COZ018-019.
UT...None.
&&
SHORT TERM...BGB
LONG TERM...MMS
AVIATION...TGJT