Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 181744

Area Forecast Discussion
National Weather Service Salt Lake City UT
1044 AM MST Wed Jan 18 2017

.SYNOPSIS...High pressure aloft will remain over the Great Basin
for the remainder of the day today. This high pressure will give
way to a series of weather disturbances beginning tomorrow and
lasting into next week.


.DISCUSSION...Morning water vapor and H5 analysis place a closed
low over the western plains, with mid level ridging remaining in
place across the eastern Great Basin. Upstream a progressive
pattern continues and is currently impacting the central/northern
coast, but am noticing amplification of the pattern further south
as a strong short wave off the NorCal coast builds amplitude. This
first trough off the NorCal coast will be the focus in the short
term through Friday as it translates east/southeast across the
eastern Great Basin and desert southwest.

Valley inversions remain modestly strong this morning beneath the
high locally, this owing to building haze along the urban
corridor, and maintenance of mature stratus over the west deserts
and Uinta Basin. Primary update made earlier only refined the
areal extent of the stratus over the west deserts to match latest
trends, as some eastward expansion occurred over the last several
hours (expansion as far east as the GSL). Do not foresee much
further expansion today with increased solar effects aloft, but
limited areal deterioration should occur to areas that are
already in it due to mid level subsidence in place. Some light
snow/flurries remain possible beneath the stratus over the next
few hours.

Primary forecast challenge today focuses on any need for
highlights regarding passage of the aforementioned trough tomorrow
through Friday. Further amplification of the upstream pattern is
expected by landfall tonight due to increased influence of a
160-180 kt jet upstream over the eastern pacific, this splitting
the trough along the CA coast while driving a more negative
tilt/upper diffluent wave passage across the eastern Great Basin
tomorrow. A modestly deep moisture tap on the eastern periphery
does look to prime the mid levels, with lift focused within the
upper diffluent sector tomorrow morning, and along the trough axis
tomorrow afternoon and evening.

P-type may be an issue for some of the western valleys along the
I-15 corridor midday, but primarily looking at a widespread light
snow event after perusing latest vertical profiles in BUFRs. Will
be taking a closer look at any potential p-type issues this shift.

Foresee in general 1-4 inches of snow for the valleys through
Friday, with the higher end across the southwest/far north and
likely the west deserts. In the mountains a decent refresher is
expected with widespread 3-6 inches with some areas closer to 10
inches in the southwest. Will coordinate with UDOT on potential
road impacts prior to any headline issuance today.


.AVIATION...With inversion conditions in place, expect
visibilities at the SLC terminal to fluctuate between 3 and 6 miles
through today. There is a 20 percent chance of IFR conditions in fog
or stratus after 18Z, but most of the lower clouds are expected to
remain northwest of the terminal. Winds may be light and variable at
times, but winds are likely to remain 7 knots or below from any
direction through the day.





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