High Wind Watch 1, NWS Salt Lake City, UT

Area Forecast Discussion
National Weather Service Salt Lake City UT
441 AM MST Mon Jan 6 2025

.SYNOPSIS...Several storm systems will track across the area into
the weekend, with snow, enhanced winds, and cold conditions expected.

&&

.SHORT TERM (THROUGH 12Z WEDNESDAY)...The latest in a series of
storm systems to impact the area is currently noted across the PacNW
through NorCal area. This positively-tilted trough will dive south-
southeast through the western Great Basin later today before
pinching off into a closed low over the desert southwest through
northwest Mexico tomorrow. Spotty showers have occurred over
northern Utah overnight, while more widespread but generally light
precipitation is starting to move into northwest Utah in a warm
advection west-northwest flow aloft. A transition to H7 cold
advection will then occur this afternoon while the flow aloft turns
more northerly, then northeasterly tonight.

A relative lack of moisture associated with this storm, combined
with somewhat diffuse dynamics and the warm advection pattern this
morning will aid to limit snow accumulations, even though the areal
coverage of precipitation across the forecast area is expected to be
fairly widespread. Latest HREF indicates a higher probability of
rain compared to snow anywhere from late morning into this evening
across many northern Utah valleys (except near the Idaho border).
Furthermore, this is supported by temperatures which did not cool
significantly overnight owing in part to cloud cover in place. By
late evening, the thermal profile will be more supportive of snow
across most areas. However, the transition to northeasterly flow
will bring a downward trend in precipitation along the Wasatch Front
tonight. Meanwhile, this will be the time when central and southern
Utah get into the action, with precipitation there continuing into
tomorrow afternoon. Overall, expect storm totals of generally 2-6
inches of snow across the mountains, with generally 1 inch or less
in most valleys. These are all sub-advisory amounts, but with the
snow and colder temperatures overnight, any snow that falls could
lead to locally slick roads which may linger into the early morning
commute.

With northeasterly flow, of course, comes a threat of
canyon/downslope winds for both the Wasatch Front and Washington
County. For the Wasatch Front, the strongest winds are expected
tomorrow morning. As far as the dynamical setup, H7 cold advection
still looks too weak to support strong downslope winds, but will
likely see at least enhanced canyon winds. The 00z HREF has a ~5-hr
window with a 40-60% chance of reaching the 45 mph Advisory criteria
tomorrow morning from Bountiful to Kaysville. This becomes only a 2-
hr window at the 50 mph threshold, while there is less than a 20%
chance of reaching 55 mph. As such, latest thinking is this will
largely be marginally advisory at best, hitting criteria briefly and
locally at favored areas such as Farmington and Centerville.
Meanwhile, the potential looks more favorable for Washington County
tomorrow evening/night, with a greater than 80% chance of reaching
45 mph by early tomorrow evening. It should also be noted that the
HREF is also indicating a 60-75% chance of reaching criteria
tomorrow morning, but am not convinced the pieces are all there yet.

As skies clear out tomorrow night, expect overnight mins to drop
more precipitously. Still, forecast mins are running only slightly
below climatological normals. However, is within a range where there
could be impacts to unsheltered populations.

.LONG TERM (After 12Z/5AM Wednesday)...Large-scale pattern through
the extended forecast period will be characterized by a significant
ridge upstream over the Gulf of Alaska/ western Canada and a mean
trough just to the east of the forecast area. Cooler, northerly flow
will be favored during this period, with potential for several
shortwave troughs to translate over the region and bring chances for
generally light to moderate precipitation events, mainly across the
northern half of the forecast area. The frequency of shortwave
impulses across the region should allow for very little development
of valley inversions through the latter half of the week.

To start the period, a departing low will be followed quickly by an
incoming shortwave trough diving into the region from interior
Canada. Cold temperatures in the wake of the previous trough will
remain in place, with only a brief period of warming before yet
another reinforcing cold front sweeps into Utah/ southwest Wyoming.
The net influence of this cold front will act to maintain
temperatures near, to slightly below, seasonal normals. This trough
will be largely moisture starved, so not anticipating much in the
way of appreciable snow for the mountains and valley areas. In fact,
there is only about a 25% chance of exceeding 0.01" of SWE in the
upper Cottonwoods and a 10% chance of exceeding 0.01" of SWE across
the remainder of the northern and central Utah mountains. In short,
keep looking toward the late week system for snow.

Speaking of that system, models are in fair agreement of a more
potent trough moving into the region late in the week/ early in the
weekend... this time containing higher moisture content. That said,
there are still some uncertainties up in the air with this system,
largely revolving around the depth of the feature over Utah. In
short, this will influence how much of the moisture we can wring
out. Confidence for snowfall is highest across the northern Utah
mountains, dropping off significantly for areas south of the
southern Wasatch. Most likely (25th-75th percentile) precipitation
amounts for upper LCC through Sunday morning ranges from 0.05"-0.35"
SWE, with similar amounts for the northern Bear River mountains.
Expanding this range into the 10th to 90th percentile shows quite
literally nothing to upwards of 0.6" SWE in favored terrain areas...
so again, there is some uncertainty to work through. With colder
antecedent surface temperatures in place in the valley areas leading
up to this more significant trough, we could see some potential for
accumulating snowfall in the lower elevation valley areas, but
anticipated impacts will heavily revolve around when the
precipitation arrives (overnight vs. commute hours).

&&

.AVIATION...Snow/Rain-snow shower activity will increase into
the morning hours, bringing a reduction in CIGs and VIS through
around 17-18Z. Showers will become more sparse thereafter, however,
there will still be around a 30% chance that the KSLC terminal is
impacted by a shower, dropping VIS/CIGs. South winds remain in place
through around 20Z, shifting northerly and remaining in place
through the evening.

.Rest of Utah and Southwest Wyoming...Increasing shower coverage of
mixed precipitation is expected through the morning hours across
northern Utah and southwest Wyoming. In area of light snowfall,
expect a reduction to MVFR to high end IFR conditions. Coverage will
decrease after 18Z as a northerly flow begins spreading into the
region. Precipitation will spread into central and southern Utah
through the afternoon and evening hours, bringing similar
conditions. Obscuration of local topography is expected through the
TAF period, especially across the northern terminals.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...None.
WY...None.
&&

Cheng/Webber

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