Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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598
FXUS65 KSLC 151614
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
914 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.

&&

.DISCUSSION...The northwestern periphery of the closed low
currently over southern New Mexico coupled with the northeastern
of a short wave near the SoCal coast continues to drive a
deformation axis over far southern Utah this morning. Suitable low
level moisture advecting northwest from the NM low coupled with
this forcing continues to drive light precip largely south of I-70
this morning, mostly in the form of light snow. This said, patchy
freezing rain has been noted in the Cedar City area as well as low
stratus and fog. Updated PoPs to expand mentionable PoPs north and
west this morning in earlier update to follow latest trends.

Short term models and Hi-res guidance do exhibit a gradual
decrease in areal extent of this precip midday/afternoon due to a
net weakening of the deformation axis and decreased moisture
advection. Maintained going forecast for the afternoon.

Outside of the south, widespread stratus and patchy dense fog
exist across central/northern Utah within the col of the trough.
A modest increase of northerly flow at the low/mid levels this
afternoon should aid to thin and or clear off the stratus in place
(largely south of Ogden), though not completely across the
central/southern Wasatch front where terrain effects will likely
aid maintenance into the overnight hours.

Eastern Utah will remain within a weak wrap around environment
into the overnight hours maintaining low clouds for roughly
another 24 hours, at which time mid level ridging will overspread
the area. Previous long term discussion below...

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.

&&

.AVIATION...MVFR conditions are expected to prevail at the SLC
terminal through 19Z with a 30 percent chance of lingering through
21Z. the TAF period. Winds will be very light (under 5 kts) and
generally from the north.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...None.
WY...None.
&&

$$

Merrill/Struthwolf


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