632
FXUS65 KSLC 082153
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
353 PM MDT Wed May 8 2024

.SYNOPSIS...A downslope windstorm will impact portions of northern
Utah Thursday morning into Friday afternoon. Gradually warming,
with daily convection, will continue into the weekend.

&&

.SHORT TERM (Through 18Z Friday)...An upper level low will
gradually weaken over the short term forecast period...slowly
shifting south and east with time.

By far the biggest impact will be the increasing likelihood of a
downslope windstorm across northern Utah. By Thursday morning,
modest cold air advection combined with easterly flow will begin
to set up the necessary ingredients. Guidance suggests the start
time will be a bit different than most windstorms, with winds
increasing Thursday morning rather than Wednesday night.

Current guidance suggests that winds will increase through the day
Thursday, reaching gusts in excess of 60 mph across the Layton to
Bountiful corridor after 00Z Friday. For other areas such as
northeastern Salt Lake County, eastern Box Elder County and
eastern Cache County, this event looks more like an extended
period of gusts in the 40-55 mph range.

To match this expected morphology, issued a wind advisory for all
prone areas, with a high wind watch from 00Z Friday onward for
Weber and Davis County. Right now, the most likely outcome (60-70%
chance) would be for wind gusts to 65 mph in this area. While
unlikely (15% chance), winds could gust as high as 75 mph in the
Layton to Bountiful area. The peak period for strong winds is
expected from 7 PM Thursday to 10 AM Friday.

As the cold air advection weakens and the easterly gradient shifts
later Friday morning, conditions will gradually improve...just in
time for a more summer-like pattern featuring afternoon and
evening convection along the higher terrain and adjacent valleys.

Given that trees are fully or nearly fully leafed out and
antecedent conditions have been quite moist, expect the threat for
tree damage will be higher with this event. Those in the prone
areas should secure trampolines, outdoor furniture, garbage cans,
decorations and other lightweight objects to prevent projectiles
that can cause property damage. Strong crosswinds may make travel
difficult for RVs and high profile vehicles along I-15, Legacy and
US-89 in Weber/Davis County and in the Brigham City area,
especially Thursday night into Friday morning.

.LONG TERM (After 18Z Friday)...Low pressure will retrograde
through Friday, and will position near the Nevada, Arizona, and
Utah border Friday evening. As it does that, east synoptic winds
will diminish, allowing strong downslope winds to diminish for
northern Utah.

With the low cut off from the mean flow, it will not exit until
later in the weekend. Scattered convective showers and isolated
thunderstorms, mainly from afternoon into evening, are likely with
low pressure to the southwest, strong lapse rates, warming of the
day, and sufficient moisture. Showers will be most common in the
mountains.

Shower coverage will be lower for the end of the weekend as the
closed low will track to the east. Isolated showers and
thunderstorms are forecasted for portions of eastern Utah,
including the Uinta Mountains. Drier conditions will build in
Monday, as ensembles are in good agreement on a longwave ridge
building off the west coast. Within northwest flow, several
shortwave troughs could track into southwest Wyoming and northern
Utah during the week. Isolated or scattered showers, primarily in
the mountains are likely with any shortwaves through Wednesday.

Temperatures Friday and Saturday will be near normal. As the
closed low exits Sunday and a ridge builds to the west,
temperatures throughout southwest Wyoming and Utah will warm
Sunday and Monday to roughly 5-10F warmer than normal, then stay
similar or decrease slightly if any shortwave tracks nearby.

&&

.AVIATION...KSLC...VFR conditions remain in place through the
valid TAF period with afternoon build-ups/ low level cloud cover
decreasing during the overnight hours. Northerly winds will
decrease in speed and gradually shift to a south wind late this
evening. That said, there is a 60% chance that light and variable
winds prevail overnight. Northeast to east winds increase in speed
tomorrow afternoon.

.REST OF UTAH AND SOUTHWEST WYOMING...VFR conditions will prevail
for a vast majority of the forecast area through the valid TAF
period, with the exception of southwest Wyoming. Near KEVW,
periods of MVFR to IFR conditions are anticipated as area snow
showers increase overnight and tomorrow morning. Otherwise, gusty
north winds are expected to develop between KCDC and KSGU tonight
and diminish by tomorrow morning, with east to northeast winds
increasing in speed across the Wasatch Front and southwest Wyoming
tomorrow. Showers will build over terrain features during the
afternoon, however, bases should remain above 5000ft AGL.

&&

.FIRE WEATHER...A slowly weakening disturbance will bring the threat of
afternoon and evening showers and thunderstorms through the
weekend. Temperatures will gradually warm, averaging around 5-10
degrees above normal by Sunday.

Strong and gusty downslope winds are expected Thursday morning
into Friday morning from Salt Lake County north and the eastern
Cache Valley.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Wind Advisory from 6 AM Thursday to 10 AM MDT Friday for UTZ103-
     105-107.

     Wind Advisory from 6 AM to 6 PM MDT Thursday for UTZ104.

     High Wind Watch from Thursday evening through Friday morning for
     UTZ104.

WY...None.
&&

$$

Kruse/Wilson/Cunningham

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