Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 260437

Area Forecast Discussion
National Weather Service Salt Lake City UT
1037 PM MDT Sun Sep 25 2016

.SYNOPSIS...Building high pressure will bring dry conditions with
a warming trend through the first part of the week. A storm
system moving up from the south is expected to bring moisture back
to the area by midweek.


.DISCUSSION...A mostly quiet evening weather-wise across Utah and
southwest Wyoming as high pressure moves in behind a departing low
pressure system and the forecast area lies under drier northwest
flow aloft. Infrared satellite imagery shows a few high clouds
clipping the northern part of Utah this evening, associated with
a weak shortwave trough sliding through the northwest flow.

Surface high pressure moving into northern Utah has set up
a modest pressure gradient across central and southern utah. This is
creating some breezy north to northeast winds across the southern
portions of Utah, especially in favored canyons aligned with the
wind direction. Models indicate that this pressure gradient will
relax tonight, allowing winds to slacken as the night goes on.

Relatively small dewpoint depressions at this hour (~5 degrees)
over some valleys of northeastern Utah and southwest Wyoming
combined with calm winds and mostly clear skies suggest some
fog is possible tonight. On the other hand, a little vertical
mixing into a dry air mass just above the surface (per model
soundings) may inhibit fog formation and result in dew or frost
instead, so any fog that does form should be thin and patchy at

Have updated the forecast to bring winds in southwest Utah closer
to observations and added a little patchy fog in the Bear Lake

.PREVIOUS DISCUSSION...ISSUED 325 PM MDT...The ridge will remain
in place tomorrow, resulting in another tranquil day with maxes
warming to near climo.

The ridge is progged to shift east Tuesday as a closed low over
northwest Mexico, once part of the storm system that moved through
the forecast area earlier this week, lifts northward into Arizona.
The resultant southerly flow over Utah and southwest Wyoming will
allow moisture to move into southern Utah. Temperatures will
continue to warm, with high temperatures running up to 5F above
climo. The low is then expected to open up and weaken as it moves
across the state on Wednesday. This will curb the warming trend and
allow for isolated to widely scattered showers across much of the
forecast area with a decent amount of moisture and instability in

.LONG TERM (After 06Z Thursday)...The weakening wave continues to
push northward through Wednesday night, with ongoing shower
development potentially impacting northern and eastern Utah.
Though the wave exits Thursday morning, enough moisture looks to
linger to allow for diurnal convective activity Thursday and

A larger trough begins to move into the Pacific Northwest Friday,
with the easternmost associated wave forecast to push across Idaho
and northern Utah on Friday night into Saturday. This wave looks
weaker than it did in previous runs, but models still produce some
QPF across the Utah/Idaho border, so have maintained primarily 30
percent POPs for now. Have also warmed temperatures a bit for
Friday/Saturday, as the best cold advection looks to remain west
of the CWA for a longer period of time.

The parent trough will likely impact the area sometime
Sunday/Monday, though models have been all over the place with the
details. For now, have kept a cooling trend with above
climatological POPs across northern Utah for Sunday.


.AVIATION...VFR conditions and mostly clear skies are expected
to continue through this evening and overnight at the SLC terminal.
Light southeasterly winds tonight should shift to the northwest
around 17z-19z Monday.


.FIRE WEATHER...High pressure has moved over the fire district,
resulting in dry and stable conditions with light winds. The ridge
will remain in place through tomorrow before shifting east.
Southerly flow will start to draw moisture into southern Utah on
Tuesday before a weak low over Arizona moves across the district
on Wednesday. This will result in an increased chance of showers
and thunderstorms and will curb the warming trend over the area.
Southerly flow is expected to increase Thursday through the
weekend ahead of another approaching trough.




UPDATE...Van Cleave
LONG TERM...Schoening

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