Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 200547

Area Forecast Discussion
National Weather Service Salt Lake City UT
1047 PM MST Thu Jan 19 2017

.UPDATE...Updated Aviation Section.


.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.


.SHORT TERM (Until 00z Monday)...The diffluent upper trough moving
east across western Utah is generating fairly widespread but
mostly light precip this evening. The exception will remain over
southwest Utah where the dynamic support for lift will remain
somewhat stronger through late tonight.

The shortwave ridge shifting east across Utah Friday will limit
precip to mostly isolated coverage, and mainly over the higher
terrain through early Friday afternoon. Increasing warm advection
southwest flow ahead of the next approaching negative-tilt trough
will bring rain/snow back in the southwest Utah Friday afternoon.
Good low-level forcing from warm advection/terrain upglide
supported by increasing dynamic lift and upper divergence with the
advancing negative-tilt trough should generate widespread and
potentially heavy precip Friday night through early Saturday.
Winter weather highlights may be issued later to address this

Significantly weaker thermal/dynamic support for lift will exist
across northern Utah as the trough passes through late Friday
night/Saturday morning. Deep layer moisture already in place
ahead of the trough should fuel widespread light to occasionally
moderate precip through at least Saturday morning. Instability
showers should persist as the coldest mid-level air moves through
the north during the afternoon.

Another somewhat stronger upper ridge will build into the western
CONUS ahead of a deep/cold upper trough setting along 130W Sunday.
Moist low-level warm advection ahead of this eastern Pacific
upper trough will reach into southwest/west-central Utah during
the afternoon. This thermally-driven lift enhanced by terrain
upglide should bring rain and snow back into much of the southwest
and west-central Utah by late in the day.

.PREVIOUS 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 northwest
flow in the lower levels. Locations where precip could linger
include the Wasatch Mountains and some of the northern Utah valleys.

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...Dense fog has developed at the SLC terminal as of
around 540Z. Visibilities below 1/2 mile with ceilings near 300
feet are expected to persist at times through the overnight
hours. There is a 30 percent chance conditions will improve to IFR
after about 10Z, however the highest confidence forecast is dense
fog will continue through about 14-16Z.


UT...Winter Weather Advisory until 5 AM MST Friday for UTZ010-015-016-




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