High Wind Watch 5, NWS Salt Lake City, UT

Area Forecast Discussion
National Weather Service Salt Lake City UT
434 AM MDT Wed Apr 3 2024

.SYNOPSIS...High pressure will shift over Utah today, bringing
warm and dry weather throughout the area. The next storm system will
begin pushing into the Great Basin Thursday, bringing strong winds
across the western valleys on Thursday, strong winds across the
eastern valleys on Friday, and accumulating mountain snow through
the weekend.

&&

.SHORT TERM (THROUGH 12Z FRIDAY)...An upper ridge is noted on
satellite water vapor imagery this morning with its axis extending
from western Montana into southern Nevada. The ridge should shift
overhead of Utah by around midday today, then continue east with the
flow aloft transitioning from northwest to southwest accordingly.
The southwesterlies are then expected to ramp up tomorrow in advance
of the next storm, which is currently noted off the BritCol coast.

Temperatures will continue to warm underneath the ridge today, with
H7 temperatures climbing to between roughly +2 and +4C across the
area this afternoon. With the ridge axis rolling over, there should
be better mixing compared to yesterday as well, especially as skies
remain mostly clear today. Most Wasatch Front valleys should see
afternoon maxes in the mid to upper 60s today, with pockets of 70F
possible, including at SLC. As winds increase tomorrow, deeper
mixing will result, and combined with a slight nudge upward in H7
temperatures (except near the NV border), temperatures will trend
even warmer, with most valleys across the forecast area in the upper
60s to 70s, which translates to between 5-15 degrees above
climatological normals. The one limiting factor against high
temperatures tomorrow would be high clouds, which should be
thickening through the day.

The thinking for the wind speeds tomorrow have not changed much. The
H7 flow is still forecast in the 35-45kt range across the western
valleys, with 50kt flow creeping in late in the afternoon. This
combined with a southerly surface pressure gradient suggests the
potential for strong gusty winds. The Thursday afternoon period is
now within the realm of the HREF, which currently indicates a 45-60%
chance of advisory criteria (>=45 mph gusts) winds across the
western Utah valleys, closer to 70% along the Nevada border. This is
a bit lower compared to the operational NBM, which tends to run a
little high. However, it is also slightly lower than the NBM 4.2.
Both the HREF and NBM 4.2 show very low probabilities of reaching
warning criteria (>=58 mph gusts) on Thursday. It should be noted
that the operational NBM shows pockets of 60-90% chance of reaching
warning criteria, but mainly over the higher elevation areas of
western Utah. Bottom line, it still looks like a solid advisory
event for the western valleys on Thursday. However, there is the
question of how much of the winds will persist into the night. The
H7 winds peak overnight when winds tend to generally decouple, but
maintenance of a southerly pressure gradient ahead of the
approaching cold front over eastern Nevada could maintain at least
30-40 mph and possibly higher gusts in some areas. No wind
highlights at this time in order to allow for daytime coordination
with partners.

.LONG TERM (After 12Z/6AM Friday)...A storm system will bring gusty
southerly winds, a potent cold front, snow in the mountains, and a
mix of rain and snow to valley locations Friday and Saturday.

A highly-amplified trough over the western portion of the Great
Basin will shift eastward from Friday through the course of the
weekend, with an associated cold front sweeping eastward through the
region on Friday.

Ahead of the front, strong southerly winds can be expected on
Friday, primarily across the eastern valleys of the County Warning
Area (east of the central spine of Utah mountains).  Wind Advisory
levels (gusts of 45 mph or greater) are almost a certainty (greater
than 90%) across the eastern valleys.  A potential for High Wind
Warning criteria (Gusts of 58 mph or higher) exists, though a large
spread in the guidance suggests medium confidence (roughly 50%).
Over the western valleys, advisory level winds are still likely (60-
70%) on Friday, primarily through early afternoon.

While showers will be possible just ahead of the cold front, the
bulk of precipitation will be post-frontal.  This stated, given
forcing along the frontal zone and decreasing stability, there is
around a 10% chance for thunderstorms along the front. Behind the
front, expect a period of steady precipitation Friday night, with
somewhat instability-driven showers continuing into Saturday. Snow
levels will drop dramatically with the passage of the cold front,
with levels reaching valley floors over all but the lower elevations
of southern Utah by Saturday morning. Though the flow is not as
conducive to orographic lift for the Cottonwoods and other northwest
flow favored areas, guidance still suggest low end advisory amounts,
with amounts of 8-12 inches.  Any accumulations across valley
locations will be limited to an inch or less, with no impacts
expected. One final item of concern with the system is the potential
for a freeze across the agricultural areas near Zion National Park,
with 25th to 75th percentile minimum temperatures near Rockville and
Springdale indicated to be 32 to 36 degrees.

A majority of ensemble members suggest a shortwave ridge will build
across the region on Sunday, providing dry weather, though roughly
25% percent of members offer a slower solution, with some potential
for showers across northern Utah Sunday morning.

For the Monday and Tuesday period, models are converging on a closed
low developing to the southwest of the Great Basin.  A roughly 50/50
split exists with whether the track of this system will be far
enough to the north to spread precipitation into southern Utah.

Ensembles are coming into agreement with a period of ridging and
warming temperatures from Wednesday onward.

&&

.AVIATION...KSLC...VFR conditions and clear skies will persist
through the valid TAF period.  Light south winds are expected to
persist through the day today, though there is a low (less than 20%
chance) that a lake breeze influence could shift winds to the
northwest.

.REST OF UTAH AND SOUTHWEST WYOMING...VFR conditions will
prevail today and tonight.  Southerly winds will develop this
afternoon and continue through tonight, with much stronger southerly
winds in store beyond the TAF period.

&&

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

&&

Cheng/Barjenbruch

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