Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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159
FXUS65 KSLC 211749
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
1049 AM MST Sat Jan 21 2017

.SYNOPSIS...The active weather pattern will continue across the
region, with a series of weather systems crossing the area through
the first half of next week.

&&

.DISCUSSION...Negative tilted trough over the area remains
progressive this morning, and have noted that the mid level
trough axis has crossed east of the Wasatch spine over the last
few hours. H5 cold pool upstream is just nosing in across
central/northern Utah further destabilizing vertical profiles,
though bulk of dynamic forcing has translated downstream of much
of the area. With continued steepening of lapse rates coupled with
low/mid level NW flow and decreasing dynamic lift, expecting
orographics to be the main player driving additional snow into the
afternoon. This can already be noted in KMTX with highest
reflectivity values along the spine of the
Wasatch/Oquirrhs/Stansbury mtns and valleys along the central
Wasatch Front.

Anticipate being able to drop Winter Weather Advisories for the
western/eastern valleys on time if not sooner as snowfall has
largely ended and orographics won`t play much of a role outside of
portions of the I-15 corridor through central Utah. Will continue
to monitor northern valleys into the afternoon, though do expect a
tapering trend in snowfall over the next couple of hours.

Building heights in advance of a low amplitude ridge will squelch
most all of the lingering mountain snow this evening allowing a
brief reprieve from active weather through much of tomorrow
morning. Did do a 2 period update to largely reduce PoPs
overnight tonight across the north.

Will be addressing some form of headlines for the next trough that
will track in rapidly late morning/midday Sunday later this
shift. Previous discussion below...

PREVIOUS DISCUSSION...Jet buckles to our west Sunday and Sunday night
shifting the ridge to our east. This next storm system has a nice
atmospheric river, thus expecting precipitation to continue to
expand in the warm advective flow. Southwest winds will be gusty
as wind field continues to accelerate with the buckling jet
arriving. 700mb winds in excess of 50 kts, building southeasterly
pressure gradient and pressure falls will support gusty winds.

Cold front quickly crosses Utah Monday according to the GFS, while
the European and Canadian are a bit slower with this progression.
Strong height falls followed by the arrival of the cold pool aloft
Monday night along with continued cold advection and northwesterly
upslope flow should bring another round of decent QPF to the
region.

Anticipate the next shift raising advisories and warnings for
tomorrow and tomorrow night. Did not want to confuse the issue
with the ongoing event on this shift.

The front end of the trough is progged to exit the area by
Tuesday morning, but cold pool instability will keep snow going,
primarily over the higher terrain of northern and central Utah,
Tuesday into Wednesday. Global models indicate this precip
tapering off behind the back side of the trough, but some
differences in timing remain. EC is a bit faster, ending most
precip by Wednesday evening but the system takes a bit longer to
move out in the latest GFS, with at least some precip persisting
into Thursday.

Behind the system, EC/GFS now both showing a drier and more stable
northerly flow with rather unseasonably cool temperatures. Overall,
models are in better agreement with temperatures, with the GFS
indicating 700 mb temps in the -14C to -16C range by Wednesday
afternoon as opposed to -12C to -14C in the EC. Both models show a
weak wave moving across Utah on Friday, but the dry airmass is
expected to limit precip.

&&

.AVIATION...At the SLC terminal...prevailing LIFR conditions are
expected to improve to high IFR/low MVFR by 21z as snow showers
taper off. Low cigs and lingering snow should hug the terrain east
and south of the terminal. Northerly winds are expected to shift
Southerly by 03z.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Winter Weather Advisory until noon MST today for UTZ005-011>016-
     020.

     Winter Weather Advisory until 8 PM MST this evening for
     UTZ007>010-517.

     Winter Weather Advisory until 5 PM MST this afternoon for
     UTZ001>004-006.

     Winter Storm Warning until 8 PM MST this evening for UTZ518.

WY...None.
&&

$$

DISCUSSION...Merrill/Dewey
PREVIOUS DISCUSSION...Rogowski/Traphagan

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