NWS Salt Lake City, UT wrote its last area forecast discussion before the first event at Nov 1, 3:11 AM MST, 9 hours 59 minutes earlier.
Area forecast discussion, Nov 1, 3:11 AM MST, 9 hours 59 minutes before
Area Forecast Discussion
National Weather Service Salt Lake City UT
411 AM MDT Tue Nov 1 2022
.SYNOPSIS...South winds will strengthen today across the region,
ahead of an approaching Pacific storm system. This system will
slowly cross the region Wednesday through Thursday. High pressure
will briefly follow late in the week, before an active westerly
flow develops this weekend.
&&
.SHORT TERM (Through 12Z Friday)...Southwesterly flow aloft has
overspread the Great Basin early this morning, downstream from a
deepening longwave trough situated along the Pacific Coast. This
trough will slowly move inland and across the western CONUS
through the short term period, impacting the forecast area with
strong southerly winds today, followed by widespread mountain
snowfall Wendesday through Thursday.
A shortwave trough currently rounding the base of the mean
longwave is approaching the northern California coast, and will
eject inland later today through tonight. As this feature
approaches, a deepening surface low across northeast NV will
induce a tightening surface gradient across western UT, and
coupled with strengthening flow aloft (50+ kts at 700mb by 00Z
this afternoon) will result in strong gusty winds across western
valleys this afternoon into this evening. This is covered well by
current wind High Wind Warning across western UT, with advisories
along portions of the Wasatch Front.
As this aforementioned shortwave ejects across the northern Great
Basin and eventually the Snake River Plain tonight, the associated
surface front will push into northwest Utah, reaching KSLC around
12Z. With the better dynamics passing north, precipitation along
this boundary will initially be fairly scattered in nature, with
the exception of the northern Wasatch/Bear River ranges where snow
will become widespread late tonight.
This surface front and trailing baroclinic zone will slowly drift
southeast through the day WEdnesday, as the upstream trough
deepens. Large scale ascent along this boundary will result in a
prolonged period of light to moderate precipitation through the
day Wednesday from the Wasatch Front and adjacent terrain to the
east, through central Utah, and eventually spreading into
southwest Utah during the afternoon. Model guidance has been slow
to lower snow levels and have generally kept a mix across the
valleys, although would not be surprised to see snow levels fall
to the valley floors along the I-15 corridor by late Wednesday
morning. Ahead of this front gusty south to southwest winds will
persist across southern Utah through much of Wednesday resulting
in breezy to windy conditions, but likely remaining below advisory
criteria.
As the upper trough progresses inland, it will slowly evolve into
a closed low across the southern Great Basin Wednesday night, and
this low will likely cross northern Arizona during the day
Thursday. Large scale ascent will become focused across southern
Utah through the day Thursday, with wrap around moisture
maintaining precipitation across the eastern valleys through at
least Thursday evening before tapering off.
Overall snowfall totals across the higher terrain from I-80 south
look to run in the 8 to 16 inch range. Depending on how long the
frontal band persists, could see higher amounts in portions of the
southern Wasatch, Wasatch Plateau, and central Mountains, however
the lack of favorable orographic forcing precludes significantly
higher mountains. Currently not expecting much in the way of
valley accumulation across northern Utah once precip transitions
over, however upper benches as well as grassy surfaces along the
valley floors could see a couple inches of accumulation by late
Wednesday evening. Further south, will need to monitor higher
terrain east of I-15 across southwest Utah, where snowfall totals
could exceed current forecast, and may need to eventually expand
the advisory into lower elevations of south central Utah if
everything comes together as currently indicated. At this time
going Winter Weather Advisories seem to handle the situation well,
and have left these unchanged.
.LONG TERM (After 12z/6AM Friday)...At the start of the long-term
period, the trough axis is expected to be just downstream of our
forecast area, with overall zonal upper-level flow building in.
While temperatures are expected to rebound slightly over the
weekend, another system will bring cooler temperatures and yet again
a chance for precipitation, this time mainly across northern Utah.
As the previous trough continues to push eastward, a very strong
zonal, upper-level jet with origins in the northeastern Pacific will
push south and into the PacNW early in the weekend. This jet, with a
core of nearly 200kts over the Pacific and around 170-180kts over
the interior west, is expected to remain just to our north during
much of the long-term period and will likely bring an increase in
moisture to northern UT and southwest WY during that period. Strong
westerly flow just to our north will allow an associated atmospheric
river to penetrate inland along the southern border of Oregon south
of the Cascades. This is one setup in which AR moisture can reach
northern UT instead of being blocked by upstream terrain (i.e. the
Sierra or Cascades). Therefore, in addition to increased winds
across UT with this jet late in the weekend, increased QPF is
expected from PWATs increasing to an ensemble mean near 0.6 inches.
Expect mainly valley rain and mountain snow with this system, with
valleys likely mixing over to snow after the frontal passage given
deterministic H7 temperatures near -10C to -12C.
The most uncertainty in the forecast lies in the progression of this
broad trough feature past its initial impact on our area. The strong
height gradient with this system is expected to continue, however
models diverge into roughly two different solutions. The first has
this broad trough continuing eastward, which would limit our overall
total QPF and lead to building heights by the end of the long-term.
About half of ensemble members portray this solution. The other half
suggest the broad trough sticks around for awhile. Given the
increased moisture, forcing, and orographic lift, this could mean a
lot of precipitation for the northern mountains, especially closer
to the ID border.
&&
.AVIATION...KSLC...Southerly winds will increase as the morning
progresses, with sustained winds to 20 knots with gusts to 30 knots
by 18Z. Winds will continue to tick up during the afternoon hours
with gusts of 35 to 40 knots possible. VFR ceilings and
visibilities will prevail through the valid TAF period, though
increasing mid and high level cloudiness can be expected. A frontal
passage will cause a shift to northwest flow around 11-13z on
Wednesday.
.REST OF UTAH AND SOUTHWEST WYOMING...South to southwest winds will
increase substantially by late morning. Sustained speeds of 20-30
knots are expected for southwest Wyoming and much of Utah, with
gusts reaching up to around 45 knots. Winds will be strongest
across the west deserts, where a few gusts could reach 50 knots this
afternoon. VFR conditions will prevail, though mid and high level
cloudiness will increase through the period. A front will bring
overall northwest flow to the area beginning very early Wednesday
morning.
&&&&
.SLC WATCHES/WARNINGS/ADVISORIES...
UT...High Wind Warning from noon today to 6 AM MDT Wednesday for
UTZ101-102-115-122.
Wind Advisory from noon today to 6 AM MDT Wednesday for
UTZ103>105-107.
Winter Weather Advisory from 6 AM Wednesday to 6 AM MDT Thursday
for UTZ110-111.
Winter Weather Advisory from noon Wednesday to midnight MDT
Thursday night for UTZ112-113-115>117-122-125.
Winter Weather Advisory from midnight Wednesday night to
midnight MDT Thursday night for UTZ126-127.
WY...Winter Weather Advisory from noon Wednesday to 6 AM MDT Thursday
for WYZ021.
&&
Seaman/Cunningham/Barjenbruch
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