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Area Forecast Discussion
Issued by NWS Salt Lake City, UT
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FXUS65 KSLC 242209
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
409 PM MDT Wed Apr 24 2024

.SYNOPSIS...An active pattern will begin Thursday and continue
into the weekend, with valley rain and mountain snow.

&&

.SHORT TERM (Through 12Z Friday)...Another mild, almost summer-
like day across the region, though enjoy this afternoon as a big
change is on the horizon. A more active pattern will begin
Thursday and continue well into the long term forecast period.

Afternoon upper air and satellite analysis indicates a slowly
weakening upper level low near the southern California coast.
Broad upper level diffluence is noted across portions of eastern
Utah. Additional disturbances associated with the continued active
northern jet are noted upstream.

Thursday looks to be quite active, with the filling upper level
low to the south and a shortwave trough crossing into northwest
Utah later in the afternoon and evening. Looks at the CAMS, most
of the members suggest a mean of around 500 J/kg of SBCAPE ahead
of a weak cold front. This combined with deep layer shear around
15-20 kts and a relatively dry sub-cloud environment will be
supportive of at least occasional dry microbursts and perhaps
occasional small hail across mainly northern Utah and Uinta
County, WY. The southern Utah convection associated with the
filling upper level low is likely to be weaker and less likely to
be electrified.

The previously mentioned weak cold front will cross the region
Thursday afternoon into late Thursday evening. Post-frontal
showers will continue into Friday morning. Temperatures will be
cooler Thursday afternoon, on the order of around 10 degrees or
so. Light snow accumulations will be possible above 8500-9000ft,
but any snow impacts will be focused on the long term forecast
period.

.LONG TERM (After 12Z Friday)...Active weather continues into the
long term period as a stronger northern stream trough begins to
dig into the region along with an attendant cold frontal boundary.
Orientation of the jet will place the area in a favorable zone of
diffluence/divergence, resulting in widespread precipitation,
especially in combination with enhanced convergence and lift along
the cold frontal boundary. Additionally, guidance shows at least
some potential for some minor destabilization, thus could see some
convective enhancement to precipitation through the day Friday,
especially along the cold front. Deep layer flow will gradually
shift from westerly to southwesterly through the day, with the
trough axis eventually moving overhead and cutting off to an
extent Friday night into early Saturday. As the trough then begins
to shift further east, will see unsettled northwest flow and
continued cold air advection maintained into Saturday, yielding
another day of elevated precipitation chances across the region.
Still a bit of uncertainty on how quickly the trough shifts out,
but general consensus is deeper scale ascent will wane overnight
into Sunday, but with enough marginally unsettled west-
northwesterly flow continuing to result in isolated to scattered
activity Sunday, particularly across the higher terrain and during
peak daytime heating.

Looking at some of the details, there is high confidence in much
cooler weather settling in with this trough. Both Friday and
Saturday will see afternoon highs drop to around 7 to 15 degrees
below climatological normal, with temperatures starting to
gradually rebound Sunday as the coldest H7 temperatures associated
with the trough depart. Similarly, snow levels Friday will
generally be around 7.5kft to 8.0kft or higher, dropping to as low
as 6.5kft or so Saturday morning, and rising back to around
7.0kft to 7.5kft during the day Saturday with daytime heating.
Exact amounts still carry some uncertainty, but general
precipitation amounts of around 0.4" to 0.8" or so of water remain
along much of the I-15 corridor, with liquid equivalent of around
0.8" to 1.6" for the high terrain across the region. As is
typical, some locally higher amounts in favored locations will be
possible. The ECMWF Extreme Forecast Index also continues to
further highlight central Utah in particular for higher chances of
seeing anomalously high precipitation in comparison to
climatology for this time of year. With sufficiently low snow
levels, this will result in some appreciable late season snow
accumulations, with the best signal noted across portions of the
Upper Cottonwoods, the High Uintas, the Manti Skyline, and the
Tushar Range. At mid elevation areas more on the fringe of the
snow level, the warmer antecedent conditions in addition to more
favorable spring sun angle (during the day) will likely help abate
more substantial accumulating snow at least to some extent.

Moving into early next week, forecast specifics will largely
depend on a deepening low dropping south from the Gulf of Alaska
and it`s downstream effects on the longwave flow pattern over the
CONUS. The general consensus carried amongst deterministic and
ensemble guidance sources is that this deepening low will help
amplify a broader ridge across much of the central CONUS, with the
local region drying/warming in turn as a result of increasing
southwesterly flow. Most uncertainty currently is noted in how
quickly this ridge develops, and in turn just how strong it gets.
For now, local forecast carries drier conditions and warming
temperatures to well above climatological normal by midweek.

&&

.AVIATION...KSLC...Northwest winds will prevail through around
04Z when winds transition to southeast. Light southeast winds will
prevail overnight, but there is a low chance that outflow winds
from showers to the northwest could switch winds to northwest for
several hours any time from roughly 06-09Z. Scattered showers and
thunderstorms are likely from 18Z into the evening.

.REST OF UTAH AND SOUTHWEST WYOMING...Isolated showers in
southwest Wyoming and northwest Utah will diminish into the
evening. Outflow winds from showers in northwest Utah could
enhance northwest flow through roughly 09Z throughout northern
Utah. Gusty southwest winds will diminish into the evening
throughout southern Utah. Scattered showers and thunderstorms are
likely for southwest Wyoming and most of Utah from 18Z into the
evening.


&&

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

$$

Kruse/Warthen/Wilson

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