Text Products for AFD Issued by SLC

Area Forecast Discussion
Issued by NWS Salt Lake City, UT
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14
000
FXUS65 KSLC 232142
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
342 PM MDT Tue Apr 23 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 relatively quiet
pattern with almost summer-like temperatures continues across the
region this afternoon. Upper air and satellite analysis indicates
ridging across the Desert Southwest with an upper level near
32N 130W.

A weak area of showers is currently nearing the Utah/Idaho border
associated with a weak front lifting northward. A weak shortwave
trough embedded in southwest flow will cross northern Utah
tonight. A few showers and maybe an isolated thunderstorm will be
possible with this shortwave trough, mainly across the northern
third of Utah.

As the upper level low continues to shift eastward through
Wednesday, an area of upper level diffluence will shift into the
Great Basin. A few relatively high-based showers/thunderstorms may
develop in response, particularly across northwestern Utah.

Very warm temperatures, averaging around 10 to 15 degrees above
normal, will continue through the short term forecast period. A
change back to more seasonal temperatures will occur in the long
term forecast period (unfortunately if you are ready for warm
temperatures).

.LONG TERM (After 12Z Thursday)...On Thursday, will see a
shortwave of fairly mild origin (H7 temps around 0C to 5C or so)
pass through the region. Enhanced lift along with lingering
moisture will trigger increasing precipitation chances through the
day, with the highest focus generally across the northern third
of the forecast region, as well as higher terrain. Additionally,
it still appears that some limited destabilization may occur
during the day (ensemble mean showing pockets of ~100-200 J/kg
CAPE), yielding a few convectively enhanced showers or
thunderstorms. While cooler than the prior day, the more mild of
the nature will yield afternoon highs still near to even slightly
above climatological normal in many locations. Additionally, with
things a bit more mild, snow levels should still generally remain
at or above 8.5 kft or so.

As the initial trough axis begins to shift east of the region, a
stronger trough will begin to approach the area from the
northwest. Stronger northern stream jet and associated increase in
upper divergence/diffluence will result in little to no break in
the overall precipitation chances, with precipitation further
maximized as a cold frontal boundary begins to push through during
Friday. Deterministic and ensemble guidance remain in good
agreement that elevated precipitation chances then linger through
Saturday as the axis of the trough shifts overhead, with only some
minor differences in regards to the overall strength/speed of the
system. Signal remains favorable that the system will be an
efficient precipitation producer, with the ECMWF Extreme Forecast
Index also continuing to highlight portions of central Utah in
particular with signal for anomalously high QPF before events end.
In any case, it looks very likely more or less everywhere will
see some amount of measurable precipitation, with current forecast
carrying 0.40" to 0.90" for many places west of Utah`s high
mountains, and widespread amounts of 0.75" to 1.50" for the high
terrain across the forecast region. Colder origins of the storm
will also allow lowering snow levels to around 7.0kft to 8.0kft
initially through Friday, and further lowering to around 6.5kft to
7.0kft Saturday as the trough axis slides in. As a result, will
see accumulating mountain snow accordingly, with some appreciable
snow accumulations possible for the highest terrain and those
typically locally favored areas such as portions of the Tushar
Range. With the cold air settling in, afternoon highs Friday and
Saturday will also be much cooler, running about 7 to 15 degrees
below climatological normal.

Uncertainty remains in regards to how quickly the system exits,
and in turn how the flow pattern evolves into early in the
upcoming week. The general consensus is the more widespread
precipitation will decrease Saturday evening into the overnight
hours, though guidance continues to show some weak energy
filtering through overhead, thus some limited precipitation
chances remain. Thereafter, the forecast region has a few
scenarios as the northern stream looks to remain active in some
capacity. Roughly 40% of ensemble members keep higher amplitude
troughing overhead, which would result in a lean towards a bit
cooler and wetter. On the other hand, around 35% of members have
the active northern stream dig elsewhere, resulting in increased
ridging overhead and in turn more mild and dry conditions locally.
The remaining 25% keep the region in a more balanced zonal type
of flow regime. For now, opted to keep NBM guidance which carries
a gradual warmup and isolated to scattered diurnal activity
(mostly northern half of the forecast region, particularly high
terrain), but wouldn`t be surprised to see exact numbers shift in
subsequent forecasts given the current spread in guidance and
associated uncertainty at this time.

&&

.AVIATION...KSLC...VFR conditions will persist for the KSLC
terminal through the period. High pressure will remain in place
resulting in mostly clear skies and breezy north winds
transitioning to a light southerly flow overnight.

.REST OF UTAH AND SOUTHWEST WYOMING...VFR conditions will persist
for the entire airspace through the period. High pressure will
remain in place resulting in mostly clear skies. Breezy southerly
winds across southern Utah will weaken overnight while central and
northern Utah/SW Wyoming maintain light and variable winds.

&&

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

$$

Kruse/Warthen/Mahan

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