High Wind Watch 5, NWS Salt Lake City, UT

Area Forecast Discussion
National Weather Service Salt Lake City UT
812 PM MDT Mon Oct 7 2019

.SYNOPSIS...
One more warm day is in store tomorrow before a strong cold front
moves through the area Wednesday, bringing wind, record cold in
some locations, and a chance of showers Wednesday/Thursday.

&&

.DISCUSSION...A predominantly zonal flow resides across much of
the western CONUS this evening, as a cold upper low along the
British Columbia coast begins to impinge on the Pacific Northwest.
Embedded within this flow further south is a weak shortwave trough
traversing the southern Sierra. The only real impact on the
forecast area is a bit of mid and high level cloud cover
spreading across central Utah. Otherwise a tranquil night looks in
store and no updates are planned. Previous discussion below
highlights the expected evolution of the approaching upper low and
remains valid.

.PREV DISCUSSION....

SHORT TERM...An unseasonably cold trough will bring a variety of
weather impacts to the area midweek. Most notably near-record or
even record-setting cold, but also windy conditions and a few snow
showers.

Tomorrow will be the peak of the roller coaster of temperatures
this week, with highs 5 to 10 degrees above normal. Breezy winds
will begin to develop late in the day over far northern Utah and
southwest Wyoming as a potent trough digs over the Pacific
Northwest and takes aim at our area.

The trough will push a cold front across the entire area
Wednesday, accompanied by gusty winds and a dramatic temperature
drop. Confidence is high on the frontal timing, consisting of
northern Utah to the Wasatch Front before noon, through central
Utah by the early afternoon, and into southern Utah by late in
the day. Locations across northern Utah will likely see their high
temperature for the day in the early morning hours before
temperatures drop into and remain locked in the 40s for the
remainder of the day. There may well be a period of wind advisory
worthy wind gusts behind the cold front passage in Castle Country
from downslope enhancement and in Washington County gap wind
favored areas by Wednesday night into Thursday morning. Currently
expecting a few snow or graupel showers with the front, but
nothing of significance given the drier continental air mass
associated with it. The best chance of showers Wednesday looks to
be east of I-15 and north of Price.

Forecast certainty at that point splits into two scenarios. The
first is a quick-moving upper-level trough passage that pushes
through Wednesday evening with the bulk of the upper-level energy
remaining well to our northeast. The latter features a secondary
piece of energy moving in Wednesday night and centered more over
northern Utah. The operational GFS has favored the former, though
a few of its ensemble members suggest the latter. The
deterministic ECMWF and ensemble split the difference while
containing hints of the latter scenario as well. The reason this
matters is the latter scenario would feature snow showers
overnight around the Wasatch Front, with plenty of instability
near the lake to potentially have lake-enhanced showers. Current
forecast is a blend of these two scenarios for now. Any showers
would be on the light side except for possible lake enhancement.
Either way, coordination with local DOT suggests surface
temperatures would preclude transportation impacts if any valley
snow showers do materialize.

The coldest air becomes entrenched across the area by Thursday
and Thursday night. Temperatures on Thursday are expected to run
about 20-30 degrees below average for this time of year, with a
widespread hard freeze, and some of the coldest temperatures yet
this season, likely by Thursday night. Current forecast would be a
record cold daytime high temperature at KSLC by several degrees
(current forecast=41, record=45 in 1880), and tie the overnight
record low (27, set in 1946).

.LONG TERM (after 00Z Friday)... The deep upper-level trough will
move out of the CWA on Friday. As a result, precipitation chances
should be nil by daybreak Friday and the gusty winds in Washington
County and Castle Country should taper off by late Friday morning.
Friday morning will also be very cold for this time of year.

Shortwave ridging will move into the region Saturday, helping to
moderate the cold temperatures. A weak broad trough will move
through Sunday into Monday before ridging looks to return Tuesday.
The sensible weather will be unremarkable through this period with
seasonable temperatures and mostly sunny skies. According to global
ensemble guidance, precipitation chances are minimal over the entire
CWA for the foreseeable future.

&&

.AVIATION...No aviation weather impacts expected during the TAF
period at KSLC terminal. Northwest winds will become southeasterly
around 03Z this evening. The shift back to northwest winds is likely
to occur around 20Z tomorrow.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Fire Weather Watch from Wednesday afternoon through Wednesday
     evening for UTZ489-494-498.

     Hard Freeze Watch from Wednesday evening through Friday morning
     for UTZ002>004-011>013.

WY...None.
&&

Seaman/Van Cleave/Jeglum

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