175
FXUS65 KSLC 092207
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
407 PM MDT Thu May 9 2024

.SYNOPSIS...A downslope wind event for portions of northern Utah
will last through much of Friday morning. Isolated to scattered
daytime rain and mountain snow showers for much of Utah will
continue Friday into the weekend. Fewer showers are likely for the
end of the weekend.

&&

.SHORT TERM (Through 12Z Saturday)...A closed low has established,
breaking off a positively-tilted longwave trough. The low,
positioned over Utah, will retrograde to near the Nevada, Arizona,
and Utah border Friday prior to absorbing into the mean flow and
exiting Saturday into Sunday.

Cyclonic flow around the low centered from central to southern
Utah has brought east synoptic flow throughout southwest Wyoming
and northern Utah. Flow at 700 mb of roughly 20 knots will
increase to 30-40 knots Thursday into Friday. The cold air
advection from higher elevations of southwest Wyoming will
strengthen a surface pressure gradient. Models have peak surface
pressure differences of around 6 mb from Rock Springs, WY to
Ogden, UT, which is a strong pressure gradient between those
locations. That cold air advection will allow for a stable layer,
or inversion near ridgetops to become established. The cold air
advection, pressure gradient, and inversion near ridgetops will
allow enhanced east flow to accelerate leeward, or downwind of the
mountains.

Hi-resolution guidance is in good agreement on wind gusts of 45
mph or more for an extended duration Thursday evening through
much of Friday morning from roughly Parley`s Canyon to Brigham
City and for the eastern Cache Valley. There is lower confidence
on wind gusts of 55 mph or more for those locations, but nearly
full agreement on wind gusts of that magnitude from Bountiful to
Layton.

East winds of 25-35 mph with gusts peaking around 55 mph are
likely for eastern portions of the Salt Lake Valley and Cache
Valley and also for Eastern Box Elder County. The typical places
locally with the strongest winds in downslope wind events will be
no different, with 35-45 mph winds with gusts around 65 mph from
Bountiful to Layton. Locally higher gusts are likely near
Farmington and Weber Canyon.

As the low retrogrades southwest, downslope winds will diminish
through Friday. Isolated to scattered convective showers and
thunderstorms are likely during the day. Most showers will be in
the mountains and will diminish once they track into valleys.

.LONG TERM (After 12Z Saturday)...The long term forecast period
begins with the closed low positioned over the NV/UT/AZ triple
point. It is then progged to shift east through the day Saturday,
with high pressure nudging into the area behind it on Sunday.
Unsettled weather is expected to continue across the area through
at least Saturday, as moisture continues to linger underneath the
low. These should be showery in nature, focusing mostly near the
spine of Utah and eastern valleys. Snow levels will continue to
rise to above 8500-9000ft as H7 temperatures should remain above
0C. This should also bring surface temperatures back up closer to
climatological normals.

Cluster analysis of model ensembles shows good agreement regarding
the egress of the low and upstream ridging. This pattern trend
should bring gradually warmer and drier weather through at least
Monday. Some northern Utah valleys could potentially reach 80F
Monday afternoon.

Thereafter, there is more uncertainty in the pattern. Cluster
analysis shows a trend towards zonal flow by late Monday, then by
midweek, there is quite a bit of spread regarding the degree of
amplification. The latest deterministic GFS and EC are both
supporting the more amplified variations, which encompass 47% of
ensemble solutions. These solutions would support more wet weather
across at least the northern Utah mountains midweek, with
temperatures moderating a bit.

&&

.AVIATION...KSLC...Gusty winds up to 30kts will continue at KSLC
through at least 02z, though these winds will likely vary between
northwesterly and east-northeasterly. Between 02-04z, winds will
transition to light and westerly (70% chance)...with low-level wind
shear also becoming a threat, given 40kt winds at 2000ft AGL. During
the overnight hours, there is a 30% chance of occasional strong
gusts out of the east due to downslope winds.

.REST OF UTAH AND SOUTHWEST WYOMING...Downslope winds will be the
main threat along the central and northern Wasatch Front and in the
eastern Cache Valley. Strong easterly wind gusts will occur through
the afternoon, especially at KOGD and KLGU. Easterly wind gusts will
likely continue overnight at KOGD, however there is a low (20%)
chance that winds transition to light and westerly, producing LLWS.
Confidence is even lower in the winds overnight at KLGU. Strong
easterly winds are more likely to persist...at least through 06z,
but at times winds may become light (also with LLWS concerns). Winds
are looking more likely to become light out of the west after ~06z.

Thunderstorms are also a concern this afternoon through 03z across
much of the area, particularly across higher terrain, with a 20%
chance of thunder at many sites. Gusty and erratic outflow winds
will be possible near these storms...notably at KPVU and KBCE.

&&

.FIRE WEATHER...Low pressure will allow for east downslope winds
for portions of northern Utah. Wind gusts will peak Thursday into
Friday, with gusts exceeding 45 mph for locations near canyon
exits, including Logan, Farmington, Weber, and Parleys Canyons.
Localized wind gusts will be around 65 mph from Bountiful to
Layton.

With the low settling near the Nevada, Arizona, and Utah border,
daily showers and isolated thunderstorms will last through the
weekend, although fewer are likely Sunday. Most showers will start
in higher terrain and could track into nearby valleys.

Temperatures will warm through the weekend as the low exits
Saturday into Sunday with more warming into the week.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Wind Advisory until 10 AM MDT Friday for UTZ103-105-107.

     Wind Advisory until 6 PM MDT this evening for UTZ104.

     High Wind Warning until noon MDT Friday for UTZ104.

WY...None.

&&

$$

SHORT TERM...Wilson
LONG TERM...Cheng
AVIATION...Cunningham
FIRE WEATHER...Wilson

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