Text Products for AFD Issued by SLC

Area Forecast Discussion
Issued by NWS Salt Lake City, UT
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FXUS65 KSLC 241026
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
426 AM MDT Wed Apr 24 2024

.SYNOPSIS...A slow moving upper level low will gradually shift
eastward into the western United States through Thursday. An
active pattern will continue into the weekend, with high elevation
snow and valley rain Thursday afternoon into at least late
Saturday.

&&

.SHORT TERM (Through 12Z Thursday)...A shortwave ridge remains in
place this morning, its axis continuing to shift east of Utah
through the day ahead of an upper low currently noted off the
central/southern California coast. Southwest flow will increase as s
result, with locally breezy conditions across the western Utah
valleys. Temperatures will continue to climb across northern Utah
(holding steady or cooling slightly across the south), with many
valleys in the mid to upper 70s and could touch 80. In general,
afternoon max temperatures across the forecast area will be around
10-15 degrees above climatological normals. Moisture increasing into
central/northern Nevada will be aided by upper diffluence ahead of
the low, producing a few showers that could move into northwest Utah
this afternoon and evening. Otherwise, a few additional, but
generally weak, showers may develop over the spine of Utah owing to
weak instability.

The upstream low will come ashore this evening, then gradually open
up and eject across northern Arizona and southern Utah tomorrow.
Precipitation will become a bit more widespread across the area, but
will be showery in nature. Even though cooler air moves into the
area, snow levels remain relatively high (above 8500-9000ft)
through the daytime hours, limiting accumulating snow and associated
impacts. Afternoon max temperatures will cool 5-15 degrees, bringing
the area closer to climatological normals. As the trough exits the
area tomorrow night, another storm system quickly enters into the
picture. This will drive continued cold advection in northwesterly
flow, with lowering snow levels, as showers continue into the night.

.LONG TERM (After 12Z/6AM Friday)...With the initial trough
downstream of the area by early Friday morning, another stronger and
more dynamic trough will follow quickly in its heels. Little, if
any, break in precipitation will be seen across portions of northern
Utah, however, there should be a distinct change in precipitation
intensity heading into the mid-morning and afternoon hours on
Friday. Additionally, this stronger Pacific trough will usher in a
reinforcing shot of cold air which will help to maintain below
normal temperatures. Conditions stabilize slightly heading through
Sunday, however, there is some uncertainty in how long unsettled
weather/ daily shower activity continue across far northern Utah and
southwest Wyoming.

Taking a closer look at the details for the Pacific trough progged
to impact the region Friday through Saturday reveals high confidence
from ensemble guidance in the overall presence of this feature. As
such, there is high confidence in both cooler temperatures and
widespread precipitation across Utah and southwest Wyoming. While
the specific details of exactly where and when the heaviest
precipitation will fall, the thinking is that there will be a band
of enhanced precipitation along a frontal boundary some time between
Friday morning and Friday afternoon. Current statistical guidance
shows the most likely range of precipitation (25th to 75th
percentile) to be between 0.30-0.70 inches from roughly Ogden
southward along the I-15 corridor through Milford. For the higher
terrain, the most likely liquid equivalent precipitation numbers are
in the neighborhood of 0.6 to 1 inch, with locally 0.8 to 1.6 inches
in the upper Cottonwoods and other favorable northwesterly upslope
regions. Given how warm the antecedent environment will be heading
into this event, snow levels will be starting around 8,000-8,500ft
MSL, dropping to 6,500-7,000ft MSL in the post frontal environment.
As we transition to a post frontal environment, orographically
enhanced precipitation will be heavily favored while valley areas
become more restricted for precipitation potential, so thinking that
the chances for any accumulating snowfall on the Wasatch Back/ other
higher elevation valley areas will be low. In general, thinking that
all impacts related to snowfall will be limited to the highest
elevations, more specifically the upper Cottonwood Canyons, as all
seasonal roads remain closed at this time.

As mentioned, there is some uncertainty revolving around how quickly
this system progresses through the region, however, a bulk of the
ensemble guidance supports the trough axis east of the area by
Sunday evening. Ridging will attempt to build into the region after
this system progresses through the area, however, there are about
60% of ensemble members that keep a more active jet stream to the
north of the area which could create an environment supportive of
continued shower activity across northern Utah and southwest Wyoming
into the middle of the week while the remainder of the forecast area
remains dry. Additionally, the uncertainty in this active jet/
trough pattern to the north of the area is also driving some
uncertainty in the temperature forecast across the northern portions
of the area. That said, expecting an overall warming trend to
establish (especially across southern Utah) heading through the
first half of next week.

&&

.AVIATION...KSLC...VFR conditions are expected to prevail through
the valid TAF period. Winds will remain out of the south through
much of the day, switching to a north flow around 00Z/6PM. There is
a 30-40% chance that winds remain out of the south through the day.

Rest of Utah and Southwest Wyoming...VFR conditions are expected to
prevail across Utah and southwest Wyoming through the TAF period.
Mid-level cloud cover will be limited to northern Utah and southwest
Wyoming late this morning and afternoon, with increasing potential
for showers across this same area through the late evening and
overnight hours. Winds across much of the area will be out of a
southwesterly direction, with peak gusts approaching 20 kts in
northern Utah/ southwest Wyoming, and 30 kts in southern Utah.

&&

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

$$

Cheng/Webber

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