NWS Grand Junction, CO wrote its last area forecast discussion before the first event at Oct 31, 10:18 PM MST, 1 hour 42 minutes earlier.
Area forecast discussion, Oct 31, 10:18 PM MST, 1 hour 42 minutes before
Area Forecast Discussion
National Weather Service Grand Junction CO
1118 PM MDT Mon Oct 31 2022
.SHORT TERM...(Tonight through Tuesday night)
Issued at 222 PM MDT Mon Oct 31 2022
A transitory ridge is overhead this afternoon, keeping skies
clear, winds light, and allowing temperatures to climb a bit
closer to normal. Clear skies tonight will allow temperatures to
drop to seasonably chilly levels after sunset, so if heading out
for trick-or- treating be sure to dress appropriately.
Winds aloft switch to southwesterly this evening ahead of the
expansive trough moving onshore of the West Coast. These
southwesterly winds will strengthen through the day tomorrow as
the pressure gradient ahead of the trough tightens up, promoting
deep mixing and bringing down some stronger winds for Tuesday
afternoon. This deep mixing will also help temperatures to warm up
to near or slightly above normal for early November, despite
increasing high level cloud cover. Winds will remain gusty into
Tuesday night, and between that and the increasing cloud cover,
overnight temperatures will remain mild. Overall, aside from
increasing winds, the next 36 hours will be quiet and mild ahead
of the next storm.
.LONG TERM...(Wednesday through Monday)
Issued at 222 PM MDT Mon Oct 31 2022
Southwest flow intensifies Wednesday, as the next PacNW low
drives across the Northern Rockies. Pressure gradients are
squeezed aloft, and the trough's leading jet merges with a sub-
tropical jet directly overhead. In addition, warm and dry
southerly flow at the surface maintains a deep boundary layer and
mixing in pre- frontal conditions. Strong winds aloft start mixing
to the surface mid to late morning, with gusts reaching 25 to 35
mph across much of the CWA. A frontal boundary will drag across
Utah Wednesday morning, creating the initial zone of enhanced lift
and line of precipitation. This band is expected to enter the CWA
by Wednesday afternoon, also increasing winds on its leading
edge. As a result, winds across eastern Utah and northwest
Colorado may exceed 40 mph ahead of this system.
Jet dynamics and qg-forcing tied with a frontal boundary will
maintain convective activity through the night, spreading showers
into western Colorado. Meanwhile, strong southerly flow ahead of
the boundary will tap into Pacific moisture and carry a plume
across the Desert Southwest overnight. This moisture advection
reinvigorates the low's AR remnants, resulting in anomalously high
PW content stretched across the Western Slope. By Thursday
morning, the trough axis centers over southern Nevada, with a
closed low predicted to cut off from northern energy Thursday
afternoon and continue an eastward trajectory towards the southern
edge of the CWA. Expect heaviest precipitation rates during this
transition with jet dynamics, PVA and upslope flow all at play.
The San Juan's are heavily favored in this flow regime, with first
dibs on additional moisture fetch and nearly-perpendicular flow
to terrain. QPF amounts have fluctuated from run to run, however,
an accumulative 1.0-1.5 inches have been a reoccurring theme
across highest terrain in the San Juan's. The frontal boundary
will also be an area of focus, as it is progged to reach a
diagonal line from Craig to GJT to Moab by sunrise Thursday. Snow
levels ahead of the front range from 7000 to 8000 ft. Cold air
advection will be dampened by terrain, prolonging the front's
progression Thursday afternoon. Thus, snow levels in prefrontal
regions will be fighting with warm antecedent conditions and
diurnal heating. Despite convective support, snow levels hover
throughout the day, with a more definitive plunge Thursday night
into Friday. By this time, the closed low drives across the
southern tier of the CWA, pushing the cold front across the CWA
Friday morning. Northerly flow in the wake of the front shifts
focus to northern aspects for snow generation. However, by this
time, most of the dynamic support and moisture source will have
exited the region. Latest WPC guidance really ramped up QPF and
snow totals, especially on day 3, to account for lower res models
washing out the combo of dynamic and orographic lift working with
PWATs approaching +2 sigma. If this trend continues with hi-res
guidance trickling in, we're looking at 1 to 1.5 feet in the San
Juans with locally higher amounts up to two feet possible. While
the northern and central mountains range from 6 to 10 inches, with
locally higher amounts up to a foot. Commute across higher
valleys and mountain passes look dicey Thursday morning, when a
mix of rain and snow to all snow at higher elevations could result
in dangerous road conditions and/or visibility. We'll see how
this system progresses tonight, wasn't ready to hoist any
highlights today. Though, expect some popping up within 24 hours.
Temperatures take a plunge behind this system. We'll have just
reached normal temps on Wednesday, and then dip back below as the
system swoops through. Highs Thursday and Friday drop 10 and 15
degrees, consecutively, below norms. Flow shifts quasi zonal into
Sunday in the wake of this week's storm, so temperatures gradually
warm but stick below normal for early November. Another wave
swooping across the Northern Rockies may return snow to northern
mountains Sunday morning into Monday. Then, the next trough
deepening along the PacNW is setting up for another round of
widespread precipitation Monday night into Tuesday. At any rate,
plenty of activity stewing upstream maintains an active pattern
this Fall.
&&
.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1117 PM MDT Mon Oct 31 2022
High level cloudiness will continue to stream in from the West
leaving cigs AOA 20KFT AGL over the next 24 hours. Wind aloft and
at the surface will also be increasing late in the forecast though
impacts to aviation look low at this time.
&&
.GJT WATCHES/WARNINGS/ADVISORIES...
CO...None.
UT...None.
&&
SHORT TERM...BGB
LONG TERM...ERW
AVIATION...TGJT