Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 150955

Area Forecast Discussion
National Weather Service Salt Lake City UT
255 AM MST Sun Jan 15 2017

.SYNOPSIS...An upper level low pressure system passing to the
south this weekend will continue to spread moisture northward
into southern Utah today. High pressure aloft will settle over
the Great Basin for the first half of the week, followed by a
return to an active weather pattern late in the week.


Water Vapor Satellite shows a deep closed low over northern Mexico,
with a deformation area over the Nevada border. A wave nearing the
West Coast is propagating through a ridge. 400-200mb MDCARS wind
observations place a 90-110kt cyclonic jet from the west coast
into Mexico and up the Southern and Central Rockies. GOES/SLC 00Z
RAOB/HRRR indicate that precipitable water values vary from
0.10"-0.15" northern mountains to 0.35"-0.55" central and
southern valleys.

Diffluent flow ahead of the closed low continues to edge east
toward the four corners region. Meanwhile as the day progresses
the deformation zone will propagate over central Utah. It will
delineate dry weather vs. chance of precipitation to the south,
and it is expected to translate across central Utah. This will aid
in areas of rain and snow lingering into the evening hours.

With a deep cyclone to our south, there is a 12mb pressure
gradient across the state which may support pockets of gusty north
winds for canyon areas of southern Utah. By the middle of tonight, on
the backside of the storm system, 700mb flow strengthens up to
30kts with a period of cold advection. Due to this, these winds
will pick up tonight and Monday near canyons and downslope areas,
and a wind advisory may be required.

The other issue in the short term comes in the way of stratus,
fog and eventually urban haze with an inversion in place. For
stratus added in additional sky coverage based on 11-3.9u
satellite and surface observations of clouds. Kept mention of
higher cloud cover for some of the more socked in basins into
tomorrow morning based on the latest WRF profiles. By then
northerly flow at 700mb should advect in drier air. Perhaps the
Western Uinta Basin remains socked in into midweek.

Finally, air quality will decline into midweek with the inversion
in place. Based on DAQ data, air quality deterioration has
accelerated. So have begun mentioning the haze by this afternoon.
This looks to last through mid week.

The ridge axis continues a southward shift as an upstream trough
is weakening the ridge. The trough axis shifts through Nevada and
into Utah by Thursday. Temperatures aloft do not appear to cool
enough to support snow to valley locations until Friday, still
with quite warm 700mb temperatures in place from warm advection
early in the week, so precip looks to be rain to start and we will
have another changing precip type event unfolding.

Both the GFS and ECMWF advertise a splitting trough feature to cross
through the Great Basin by late in the week. With this solution, a
messy uncertain track of the upper level trough is in play. Plenty
of time for many changes to be resolved in the models, so don`t have
a strong gut feeling one way or another how this will play out
besides the fact that another unsettled and wet end to the week is
in store. Both operational global models are in decent agreement
with the large scale pattern; the trough splitting and sweeping
through the Great Basin Thursday into Friday, with an upstream
kicker trough. What`s interesting is how quickly the GFS continues
to push out that first trough only to dig a deeper Low with a bit
more energy southeastward into Nevada and northern Arizona by
Saturday. The ECMWF meanwhile has more of an open wave trough
swinging through Nevada and Utah into Saturday while the main low
center remains in the Pacific Northwest.

Both operational models highlight cooling temperatures aloft able to
support snow to Valley floors, however, with that said a southwest
flow aloft advecting in relatively warmer air over the cooler air
may play a part in potential for freezing rain. Will be an
interesting end of the week to watch as we go into the weekend.


For the KSLC terminal, MVFR ceilings will persist through midday
before lifting. Visibilities may dip into MVFR briefly through
18z, with a 30 percent chance of IFR vis after 12z. Winds will
remain light and northerly through the TAF period.




SHORT TERM...Rogowski

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