Area Forecast Discussion
Issued by NWS Salt Lake City, UT
FXUS65 KSLC 192350
Area Forecast Discussion
National Weather Service Salt Lake City UT
450 PM MST Thu Jan 19 2017
.SYNOPSIS...An active pattern will continue across the region, with
a series of weather systems crossing the area through the middle
of next week.
.SHORT TERM (THROUGH 00Z MONDAY)...An upper trough continues to
approach the area this afternoon with the bulk of its energy still
expected to track across southern Utah and northern Arizona tonight.
Meanwhile, a moist airmass and weak embedded disturbances will
continue to maintain areas of generally light precipitation across
Cold advection northwesterly flow has developed across northern Utah
which has helped to bring periods of enhanced snow to the Wasatch
Front and adjacent mountains. However, with temperatures hovering
near freezing, snow accumulations have been minimal in many valleys
and on treated surfaces. Snow may tend to accumulate with more ease
near/after sunset, but drier air spreading from the northwest is
expected to bring a gradual end to the snow.
Models still indicate precipitation focusing across west-central
Utah through this evening along an area of 700mb convergence and/or
weak circulation. As such, the best valley accumulations tonight
looks to occur in this area. Otherwise, expect snow to also continue
to fill in across southwest Utah with the approaching trough, but
valley accumulations will generally remain light.
Have cancelled the Winter Weather Advisory for UTZ005 due to the
aforementioned drying trend across the northwest, otherwise have
left remaining Advisories in place.
Precipitation will taper off tomorrow morning through early
afternoon as the trough exits the area and a weak shortwave ridge
builds in. However, this drying trend will not last as the active
weather pattern will continue with the approach of the next trough.
This trough will start to bring moisture into southwest Utah
tomorrow afternoon as southwesterly flow increases across the area.
With the bulk of the energy diving even farther south into Arizona
than tonight`s trough, the higher snow accumulations will remain
over southern Utah. However, weak embedded disturbances will cross
northern Utah so accumulating snow will be possible across the north
as well. Some zones, especially the central and southern mountains
and higher valleys of southwest Utah, may see enough snow to warrant
a winter weather highlight, but will wait until after the current
storm starts to wind down to address this. However, with a slightly
warmer airmass in southwest flow during the initial portion of the
storm, rain may mix with snow in some valleys through around midday
Saturday before colder air spreads into the area in northwest flow
behind the trough axis.
Precipitation will wind down again Saturday night as a shortwave
ridge builds into the area once again. Increasing southwesterly flow
ahead of the next storm will then spread moisture back into the area
beginning on Sunday.
.LONG TERM (After 00Z Monday)...The large trough continues to push
across the western CONUS on Sunday night, with a strong and moist
southwest flow over Utah and southwest Wyoming. Have increased the
forecast southerly winds and warmed temperatures for Sunday night
into Monday morning, as the southerly gradient increases
significantly ahead of the bulk of the trough. These southerly winds
may have to be pushed even higher on future shifts.
Have also kept POPs fairly high through Sunday night and Monday,
with widespread precipitation likely under good jet dynamics and
increasing mid-level cold advection. Locations favored in southwest
flow will do best until Monday morning, then low level winds will
switch to the northwest as a decent low level baroclinic zone pushes
across the CWA through 00Z Tuesday.
After 00Z Tuesday, the jet and the best dynamic forcing shift south
and east of the area, which could shut down precipitation in many
locations. However, some snowfall will persist through Monday night
and perhaps into Tuesday in continued cold advection and
northwesterly flow in the lower levels. Locations where precip could
linger include the Wasatch Mountains and some of the northern Utah
This is a fairly cold storm system once the trough axis swings
through fully, with 700mb temperatures forecast to drop as low as
-14C to -16C through much of Tuesday and Wednesday, and perhaps
lingering into Thursday. Have generally cooled temperatures through
this day 5-7 period, and they may need to be lowered even further as
confidence grows, especially if an overnight period can be
identified that will actually clear clouds out of the area
efficiently. This could be Wednesday night or Thursday night, as a
strengthening ridge builds over the western CONUS at the end of the
week and heading into next weekend.
.AVIATION...IFR conditions in snow will likely continue at the SLC
terminal through 01Z, with a 30 percent chance that showers continue
to linger in the 01-04Z period. A chance of showers continues
overnight, but any showers after 04Z should be relatively brief.
Winds should continue to be light and variable through at least 06Z,
with speeds generally remaining 7 knots or less.
UT...Winter Weather Advisory until 5 AM MST Friday for UTZ007-008-
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