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This is Glen Merrill…forecaster with the National Weather Service in Salt Lake City.
Today is Wednesday December 18th, and this briefing will cover a tricky storm set to hit
northern Utah tomorrow. The good news is that valley inversions look to break, we’ll
just have to go through a bit of mess to do that.
We’re expecting 4 main impacts with this storm. Hazardous and icy travel conditions are
expected to develop across the northern valleys after midnight tonight and linger through the
a.m. commute with some freezing rain expected, before changing to snow that will then impact
the p.m. commute (See UDOT for more info on travel impacts). This accumulating snow is
expected to be significant north of roughly Provo for both the valleys and mountains, and
with this snow watch for an increase to avalanche danger in the mountains (See the UAC).
Some good news is that this storm will clear out valley inversions, resulting in
improved air quality. (See DEQ)
So what is freezing rain? Freezing rain occurs when snow falls from cold clouds above the
surface. This snow then moves into a relatively warm layer of air above the valleys and melts,
becoming rain. Due to the inversions over the past several days, a cold layer
persists across the valleys of northern Utah. This cold layer is relatively shallow, so the
rain is unable to refreeze before reaching the surface. Many surfaces will be below
freezing due to the cold temperatures over the past few days. As the rain hits these
cold surfaces, it then freezes again and begins to accumulate as ice. The most prone
surfaces include roads, trees, powerlines, and bridges. That’s what it is, so where are we
expecting it…
The areas highlighted in orange are those most likely to see freezing rain late tonight into
tomorrow morning. The most prone are the lowest valley areas near the Great Salt Lake,
Utah Lake, and the Heber Valley. I-80 from Grantsville to Salt Lake City, I-15 and the
Legacy Parkway north from Salt Lake City to Farmington will be the most prone. The Cache and
northern Front should see mostly snow…with some rain mixing into some of the benches
of the Salt Lake and Utah valleys…though freezing rain is possible those areas and the
others in yellow.
Timing and amounts: The precipitation is expected to begin along the Wasatch Front
around midnight with some freezing rain and rain valleys, mixed rain and snow mid
elevations, and the northern Front and Cache, and all snow in the mountains. This mixed
precipitation is expected to change to all snow mid to late morning with significant
accumulations expected…generally Provo and points north.
Bottom line: Three main take aways to focus on from this briefing and storm. First,
leave early tomorrow and expect slick and icy conditions across the metro area. Second, plan on
snow lingering into the evening commute impacting that as well. But third, and the best
news…valley inversions are expected to break up after the storm.
Thanks for watching! If you have any questions feel free to send us an email. You can also like
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