783
FXUS65 KSLC 212257
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
357 PM MST Thu Nov 21 2024

.SYNOPSIS...Warmer than normal, dry conditions will last through
Friday. Several storm systems will track into southwest Wyoming
and Utah, with rain and snow into the weekend and next week.

&&

.SHORT TERM (Through 12Z/5AM Saturday)...A longwave trough off the
coast of the PacNW is associated with a surge of moisture
advection into Oregon, Washington, and northern California. This
atmospheric river event is bringing rain and mountain snow to
those states. A southwest synoptic flow has the storm track north
and west of southwest Wyoming and Utah. Limited moisture advection
from that atmospheric river has pushed in with clouds for
southwest Wyoming and northern Utah. Enhanced south to southwest
flow pushed temperatures to around 10F warmer than normal.

Minimal change is likely Friday, as the trough off the coast of
the PacNW will track slightly eastward. Temperatures will be
around 10F warmer than normal throughout, with more clouds in
southwest Wyoming and northern Utah than further south. Winds
will increase from the south to southwest, with gusts around 30
mph in southwest Wyoming and southwest Utah.

.LONG TERM (After 12Z/5AM Saturday)...The forecast remains
relatively unchanged through the past few model runs. A majority
of guidance suggests an active period upcoming with a shortwave
moving through on Sunday that will bring a cold front with
moisture from a decaying atmospheric river resulting in valley
rain and mountain snow. A brief period of shortwave ridging late
Sunday through early Monday will bring a lull in activity before a
strong westerly jet brings another moisture surge ahead of a
deeper trough moving onshore that could bring a transition to
valley snow by Wednesday.

Synoptically, a 981 mb mid-latitude cyclone is spinning off the
coast of British Columbia. This is helping advect an atmospheric
river into the PNW from northern California through British
Columbia. This area of low pressure will continue to remain offshore
through midweek. As it rotates offshore, shortwaves will circumvent
the periphery and bring moisture and a cold front to our CWA by
Sunday. Ahead of the impending shortwave, southerly flow will
increase as the pressure gradient tightens. This will enhance
southerly surface winds on Saturday, particularly across southern
Utah. There is a high chance that winds eclipse wind advisory
criteria for portions of western and southern Utah, but wind warning
criteria currently remains a low chance and confined to far
southwestern Utah on Saturday afternoon.

The shortwave will push a cold front through the region early Sunday
that will bring valley rain and mountain snow (snowlevel ~5000 feet)
along the front. This front still looks to stall across central Utah
during the day on Sunday before transitioning to a warm front that
will bring a return to southerly flow and increased moisture on
Monday. This will help to enhance precipitation areawide on Monday
with snowlevels rising 1000-1500 feet compared to Sunday.

On-and-off precipitation will continue through the middle of the
week as moisture remains in place and a 100+kt westerly jet provides
weak widespread ascent across the area. The aforementioned low
pressure off the PNW coast will likely (~65% chance) move inland on
Tuesday with an arrival to our area on Wednesday. This will make for
the most opportune period for the heaviest precipitation rates and
snowlevels falling to valley floors behind a frontal passage as H7
ensemble mean temperatures are forecast to drop as low as -11C. The
trend in the last several model runs have pushed the trajectory of
this trough further south, which would bring the highest QPF totals
to central and southern Utah. There remains a large range in totals
across the region, suggesting that there is still a lot of
uncertainty regarding the track of this trough. In addition, ~35% of
ensemble members keep this low pressure off the coast through the
period which would result in a drier and warmer scenario.

&&

.AVIATION...KSLC...Light northwest winds will last through 03Z,
with light southeast winds from 03Z into the afternoon. Southeast
wind gusts around 25 mph are likely much of the afternoon.
Scattered to broken clouds in VFR range will last through the
day.

.REST OF UTAH AND SOUTHWEST WYOMING...Relatively light winds will
last through the morning. Winds will increase for the afternoon,
with southwest wind gusts around 30 knots in southwest Wyoming and
southwest Utah. Southwest wind gusts around 25 knots are likely
for other portions of Utah. Scattered to broken clouds are likely
for southwest Wyoming and northern Utah, with mostly clear
conditions elsewhere.

&&

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

&&

$$

SHORT TERM...Wilson
LONG TERM...Mahan
AVIATION...Wilson

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