Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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000
FXUS65 KSLC 142258
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
458 PM MDT Thu Mar 14 2024

.SYNOPSIS...Easterly downslope winds expected to become significant
overnight into Friday morning for prone areas of the northern
Wasatch Front as well as portions of the eastern Cache valley. A
weaker downslope event looks possible Friday night into Saturday
morning. Additionally, closed low will bring substantial snowfall to
much of southern Utah through late Saturday, with forecast
accumulations some of the highest of the season.

&&

.SHORT TERM (Through 00z Sunday/06 PM Saturday)...

* Key message 1: Strong wind gusts are already ongoing along much of
  the northern Wasatch Front. Stronger and more significant winds
  are expected to develop this evening, and persist through the
  overnight hours.
    * For eastern Weber and Davis Counties at areas along and east
      of I-15 and US-89 corridor, northeast winds 30 to 40 mph
      with gusts up to 70 mph expected. Gusts up to 80 mph are
      likely for the Park Lane to Centerville area, with a 10
      percent chance for these areas to see wind gusts in excess
      of 80 mph. Areas west of I-15/US-89 will see substantially
      weaker winds.
    * Across northeastern Salt Lake County (approximately near the University
      of Utah to Parleys Canyon), northeast winds around 25 to 35
      mph with gusts up to 60 mph expected.
    * In portions of the eastern Cache Valley (generally
      along/east of US-91) and eastern Box Elder County,
      northeast winds 20 to 30 mph with gusts up to 60 mph
      expected. There is a low chance (20%) winds on the eastern
      side of Cache County and near Brigham City will exceed 70
      mph.

* Key message 2: Southeastern to south central Utah still appears
  likely to experience one of, if not the most substantial snow
  event for the year. While some uncertainty is noted, snow levels
  as low as 5000 feet at times will promote accumulating snow in
  areas which see it much less frequently. Accumulations increase
  significantly with elevation, with snow accumulation of 1 to 2
  feet for the mountains west of US-89, and snow accumulation of 2
  to 3 feet, locally up to 4 feet mountains east of US-89.

Afternoon GOES water vapor imagery showing the ensuing setup
nicely this afternoon, with a cutoff low continuing to settle into
the Desert Southwest near the NV/CA/AZ border region. With strong
ridging concurrent through the PacNW, strong and very anomalous
easterly 700mb has developed aloft. So far through the afternoon,
this has been resulting in more of a hybrid type of downslope wind
event, with wind gusts a bit more modest (generally 40-60 mph or
so), but a bit more widespread rather than constricted to areas
nearer to the terrain due in part to thermal mixing. The biggest
change in comparison to prior forecasts is that it now appears the
best juxtaposition of favorably oriented pressure gradient and
700mb flow along with cold air advection will occur from late
Friday evening overnight into Friday morning. With thermal mixing
decreasing, anticipate wind gusts to begin to pull back nearer to
the terrain, but given the increasingly favorable setup, will see
wind gusts increase with conditions still looking good for a
period of more significant wind gusts overnight in the favored
downslope areas. The best signal and highest confidence remains in
the eastern Davis/Weber County area, generally east of the I-15
and US-89 corridor, and particularly between roughly the Park Lane
to Centerville area. Substantial winds still also look fairly
likely across downslope wind prone areas in northeast Salt Lake
County, eastern Box Elder County, and portions of the eastern
Cache Valley. Aside from these areas, less typical downslope prone
areas (including the Western Uinta Basin and portions of the US-6
corridor near Price to Sunnyside) which have seen some modestly
gusty conditions today will start to see improving conditions
sometime after midnight as the flow overhead shifts a bit.
Overall, opted to continue all wind based headlines accordingly.

The strongest winds will begin to subside by late Friday morning
on into the early afternoon hours. That said, with the center of
the cutoff low continuing to churn more or less in the same
position, easterly flow will persist over those same downslope
prone areas in northern Utah. The combination of ingredients
overall will be a bit weaker (a bit weaker flow / gradient / cold
air advection), but high resolution guidance has started to
highlight the potential for more modestly strong (more in the
40-55 mph range) downslope winds in prone areas once again late
Friday evening into Saturday morning.

Aside from the wind, this cutoff low will be responsible for
potentially the snow event of the year for southeastern and south
central Utah. Position of the low will help pull Pacific moisture
into more typically shadowed locations, and with ample synoptic
forcing from the low itself and modest jet support, will see a
favorable setup for fairly widespread precipitation. Given the
cold core of the cutoff low will be in vicinity, 700mb
temperatures will be cold enough to bring snow levels down to
around 5000 feet at times (particularly overnight into Friday
morning). Some uncertainty is noted, but will see potential for
accumulating snow in areas that dont frequently see it, and as a
result those with any travel plans should remain aware of the
possibility of winter driving conditions along lower elevation
routes that may typically not see snow. Again, uncertainty is
noted, but current forecast includes around 2 to 5 inches of snow
in such areas across portions of south central Utah.

Low level temperatures will moderate/warm some moving further
into Friday, and as a result snow levels will begin to increase.
This will result in precipitation changing back to rain in many of
those lower elevation locations through the day, but as diurnal
heating ceases moving into Friday night/Saturday morning, snow
levels will drop back to as low as 6250 feet or so, and some
locations will see a switch back to snow accordingly. A similar
diurnal cycle is then expected through the day Saturday with
precipitation lingering as the closed low makes minimal progress.
Overall, by the events end, some of the more traveled areas of
places like Bryce Canyon and Capitol Reef could see snow totals in
the 6 to 12 inch range. Meanwhile, the mountains will see
substantial snow accumulations given continued snow throughout the
event, and with atypical moist easterly upslope flow, mountains
east of US-89 will be more favored than those west. Forecast
numbers ticked up slightly, with a general 1 to 2 feet forecast
for the mountains west of US-89, and 2 to 3 feet for the mountains
east of US-89. Some localized amounts of 4 feet will be possible
in those eastern mountains, such as Boulder Mountain.

.LONG TERM (After 00Z Sunday / 6PM Saturday)...
On Sunday, precipitation will continue to wind down across southern
Utah, with minimal additional snow accumulations, as the forcing
from the low wanes as it starts filling more.

The main trend in the extended is a potential resurgence of
downslope/canyon winds Saturday night into Sunday morning for the
favored areas along the Wasatch Front. This potential hinges on the
details of the track/strength of the meandering closed low near Las
Vegas, and thus not being too bullish with the forecast at that time
given the uncertainty around the low track. However with the low to
our south and the potential for continued cold advection out of
Wyoming, this will be something to keep an eye on. For now, have
introduced some advisory to sub-advisory level winds in the most
favored locations (40-50 mph gusts).

Otherwise, the remainder of the extended is relatively quiescent as
Rex Block anchors over the Western US, featuring a anomalous 500 mb
heights over the Pac NW / British Columbia to our northwest, with
the closed low remaining nearly stationary near Las Vegas / northern
Arizona. This will setup a warming and drying trend across northern
Utah into next week, pushing daytime highs largely 4 to 8 degrees
above average through early to mid next week. Meanwhile with the
proximity of the closed low to southern Utah, temperatures will be
recovering from around 5-10 degrees below normal to start the week
to around normal by mid week.

&&

.AVIATION...KSLC...Gusty east/northeasterly winds will be the main
concern for the terminal through the TAF period as a downslope wind
event continues into Friday. Expect to see northeast gusts to around
30 knots persist through around 03Z before winds constrict back
toward the terrain overnight. This will setup a period of light
surface winds which will likely back around to the southeast.
However, with mountain waves developing from the downslope winds,
expect to see low-level wind shear overnight as winds off the
surface remain from strong from the east/northeast. During the day
Friday, expect to see northeasterly wind gusts redevelop at the
surface, which will limit the LLWS threat.

.REST OF UTAH AND SOUTHWEST WYOMING...The main hazard across
northern Utah through Friday will be the downslope wind event, where
the most prone terminals like OGD/HIF will weak peak wind gusts from
the east to 40-60 knots. Otherwise, low level wind shear will be a
concern for terminals along the Wasatch Front tonight as winds aloft
remain strong out of the east but winds decouple at the surface. For
southwest Wyoming, expect MVFR conditions from lingering snow
showers and low CIGS to improve overnight into Friday morning. For
southern Utah, a widespread winter storm system will focus periods
of heavy snow with IFR conditions into south-central/southeast Utah
Friday through Friday night.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Wind Advisory until midnight MDT tonight for UTZ101-113-114-120.

     High Wind Warning until noon MDT Friday for UTZ103>105-107.

     Wind Advisory until noon MDT Friday for UTZ108-110.

     Winter Weather Advisory until 6 PM MDT this evening for UTZ112.

     Winter Storm Warning until 6 PM MDT Saturday for UTZ117-125-127-
     129.

     Winter Weather Advisory until 6 PM MDT Saturday for UTZ128.

WY...Winter Weather Advisory until 6 PM MDT this evening for WYZ021.

&&

$$

SHORT TERM...Warthen
LONG TERM...Church
AVIATION...Church

For more information from NOAA`s National Weather Service visit...
http://weather.gov/saltlakecity


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