Area Forecast Discussion
Issued by NWS Salt Lake City, UT
FXUS65 KSLC 172245
Area Forecast Discussion
National Weather Service Salt Lake City UT
345 PM MST Fri Feb 17 2017
.SYNOPSIS...The upper level trough off the California coast will
send moisture along with a series of weather disturbances across
Utah through the weekend. High pressure aloft will return early
next week, followed by another round of active weather midweek.
.SHORT TERM (Through 00Z Tuesday)...The forecast area is under a
moist southerly flow this afternoon ahead of a large system off
the California coast. PWs are in the 0.4 to 0.6 inch range across
Utah and southwest Wyoming, near the maximum observed this time of
year. Ahead of the trough, a shortwave is lifting northward across
the state, providing instability to produce increasingly
widespread precipitation. Given the mild airmass, snow levels
remain quite high (7500 feet or so), so snow related impacts are
confined to higher terrain locations.
Southern Utah will see a temporarily lull in precipitation this
evening and overnight as the ejecting wave continues north,
shifting the focus of precip to northern Utah. As northern Utah
precip diminishes Saturday morning, it will increase again over
southern Utah as the main trough continues east. This system is
progged to cross the Desert Southwest Saturday night into Sunday,
bringing a frontal boundary across the forecast area from east to
west. 700 mb temps are expected to drop to as low as -6C by Sunday
afternoon, dropping snow levels to around 6000 feet. Overall
intensity of precipitation is expected to be greater with the
front than with the more warm advection based precip observed
today or tonight, so winter weather highlights may be needed for
the higher terrain.
High pressure is progged to move over the area Sunday night into
Monday behind the exiting trough. Latest GFS indicates precip
increasing over northern Utah Monday afternoon in warm advection
southwest flow. However, the warm advection is much weaker in the
EC solution, and so it shows a lot less in the way of precip.
.LONG TERM (After 00Z Tuesday)...Weak shortwave ridging begins to
break down moving into Tuesday with another quick moving low
pressure trough swinging into the Pacific Northwest. As mentioned
by the previous long term discussion/shift, the EC looks to be the
much better consistent solution with the extended forecast period.
With regards to ensembles and deterministic model runs, it does
appear that the EC ensemble suite and it`s operational counterparts
remain in rather good agreement through the latter part of next
week, compared to the GFS ensemble and operational members.
Warm advection, southwest flow ahead of the Pacific trough is
advertised well by global models through late Tuesday. The EC has
been more consistent in timing and strength compared to the GFS, but
the overall pattern remains the same. Took a more modest blend of
models and tweaked PoPs down a bit while retaining the overall
trend. The cold front for Wednesday will work to drop snow levels so
that most valley locations will see snow, as 700mb temps drop into
the negative double digits by late Wednesday night (-10C or so). As
the best plume of precipitable water and forecast QPF drastically
declines by Thursday, the northwest flow aloft may struggle to
produce significant high elevation snow for the latter part of
Thursday into Friday. Models also diverge in solutions by this
point, so confidence is a bit low. However, cold air aloft looks to
remain in place through the end of the week, cooling daytime
temperatures back below normal, with overnight temps back below
freezing for most valley locations.
.AVIATION...Ceilings at the SLC terminal should primarily remain
below 7000 feet between 23Z and 05Z, with a chance that these cigs
persist through 10Z. There is also a 20 percent chance of MVFR
conditions in rain showers through 05Z. Light and variable winds as
of 2230Z are expected to increase from the south around 23-01Z.
Nearby shower activity could make these winds gusty and/or erratic
at times through 05Z.
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