Area Forecast Discussion
Issued by NWS Salt Lake City, UT
FXUS65 KSLC 121218
Area Forecast Discussion
National Weather Service Salt Lake City UT
518 AM MST Thu Jan 12 2017
.SYNOPSIS...A low pressure system moving south along the west
coast will bring one final round of precipitation to much of Utah
today and tomorrow. High pressure aloft will then settle over the
region for latter half of the weekend. The next stormy period
looks to be towards the middle of next week.
.SHORT TERM...A complex and dynamic weather situation continues to
unfold across the Intermountain West this morning. Infrared
satellite imagery shows a circulation center moving down the CA
coast, with an associated deformation zone downstream extending
across the Great Basin and into our area, accompanied by rapidly
cooling cloud tops moving into UT. Area radars show scattered
light showers over northern UT, and more widespread precipitation
in the mountains of southern UT. Surface observations depict a
hint of a boundary across northwest UT, with colder temps and
northerly winds across the Bonneville Salt Flats.
Forecast models have trended farther north with the synoptic lift
today/tonight vs yesterdays runs, meaning a threat of
precipitation now stretches as far north as the Cache Valley and
southwest WY. There are plenty of things working in favor of
widespread precip for our area; healthy mid-level WAA, strong
forcing aloft as the favored exit region of a 110kt 300mb jet
noses into the center of the state, and a potential low-level
baroclinic zone as colder air moves in from the northwest.
The tricky part of the forecast for valley locations today (in
addition to the questions of how far north widespread precip will
reach) is the potential for snow levels rising above valley
floors, especially this afternoon. Wet bulb temperatures are
currently near freezing currently across the Wasatch Front.
Shallow colder air is present just to the northwest, but may
stall there today, while WAA is expected just above the surface.
Current guidance suggests rain could mix in as far north as SLC
today, with central UT valleys and West Deserts south of I-80
having the best chance of changing to rain. On the other hand,
more intense banding is still expecting from about Provo to
Beaver, which could push snow levels back to the surface and lead
to road surface accumulations as far north as Utah Lake vicinity.
Considering all these variables, have opted to leave current
highlights mostly unchanged, meaning winter weather advisories
continue for valleys from around Provo to Beaver. Will continue to
monitor for potential expansion of advisories farther north.
Benches and higher elevations will see another round of moderate
to perhaps heavy snow at times by mid-day. Mountains from central
UT to the Uintas should fare the best, with 6" to over a foot
expected. The most notable travel impacts today will likely
stretch from the Wasatch to Castle Country and the western Uinta
The upper-level closed low will continue to swing down the SoCal
coast tonight and Friday, eventually pushing inland through Baja
Friday/Saturday. This will bring drier air to northern Utah by
tomorrow, causing precip to wind down to a few showers over the
higher terrain. Widespread light to moderate snow is expected to
continue over central and southern UT meanwhile as modest isentropic
lift continues and a weak baroclinic zone shifts south. With
potential for heavy snow along US-89, have issued an additional
advisory for southern UT mountains today into tomorrow. Precip
should eventually diminish Saturday, though models have trended
slower with the low track, hinting that showers could continue
into the weekend, especially for southern UT mountains.
.LONG TERM (After 00z Sunday)...Extended period forecast models
being the second half of the weekend with rotating the desert
southwest low farther south and east, giving way to a deformation
zone overhead of Utah and Nevada. Little forcing or jet support and
diminishing moisture would suggest a drying trend to end the
weekend. Speaking of a deformation zone, by late Sunday the far
southeast portion of Utah looks most favorable for lingering showers
to develop/continue under this pattern.
As a transition day Monday, the next baroclinic front is advertised
to enter northwest Utah Tuesday morning, as the northerly flow aloft
shifts to a flow from the northwest. The sharp positively tilted
ridge brings another active pattern to the west coast, as we again
see warm advection ahead of a trough spinning onshore of the Pacific
Northwest coast. Even though 700mb temperatures will see a slight
warming trend, cold air in place near the surface should keep an
inversion in place for many valley locations. Global forecast models
are in decent agreement through the extended, which hasn`t happened
much this winter it seems. By late next week a cold front is
expected to push through the Great Basin as the PacNW trough dives
into the Desert Southwest, scouring some cold air into the area.
Snow levels through this period are largely unaffected through
Thursday, when this cold front pushes through. Another active period
for the next week or so is expected.
.AVIATION...LIFR conditions at the SLC terminal are expected
to persist through mid morning in fog and low clouds, due to nearby
showers. Expecting conditions to improve to IFR in rain/snow mix by
15z and remaining high IFR/low MVFR through the majority of the
afternoon. Winds are expected to stay from the north with periods of
light and variable possible through the afternoon.
UT...Winter Storm Warning until 11 PM MST this evening for UTZ006>010.
Winter Weather Advisory until 11 PM MST this evening for UTZ004.
Winter Weather Advisory until 11 AM MST Friday for UTZ014-015-
Winter Weather Advisory until 11 AM MST Friday for UTZ011-012.
SHORT TERM...Van Cleave
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