566
FXUS65 KSLC 262159
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
359 PM MDT Fri Apr 26 2024

.SYNOPSIS...An active pattern will continue through the weekend,
resulting in valley rain and mountain snow along with continued
cool conditions. Modest warming is then anticipated into midweek
with a weak, grazing system brining a few showers to northern Utah
and SW Wyoming on Monday afternoon.

&&

.SHORT TERM (Through 12Z/6AM Sunday)...Early Friday afternoon
analysis indicated the presence of a strengthening trough across
the Southern Great Basin, with an organized shortwave across
southern Nevada and jet axis rounding the base of the trough
across Arizona and Southern California. These features are
presenting themselves quite nicely on mid-level WV this afternoon.
This is placing western portions of Utah and eastern Nevada within
a favorable region of upper diffluence/large-scale ascent.
Farther north across northern Utah, a lingering low to mid level
circulation (what appears to be the upper low coming together)
continues to serve as a focus for shower and thunderstorm
development and maintenance. Instability is quite modest across
northern Utah this afternoon, with fairly equally modest PWATs
in the 100-150% of normal range. However, SLC 12Z sounding
revealed a deep, saturated layer up to the tropopause and a
modest, tall, skinny CAPE profile. As a result, we`re able to take
advantage of the available moisture and squeeze out widespread
showers with locally heavy cores and occasional lightning.
Finally, over southeast Utah, breaks in the clouds have allowed
for surface-based instability/buoyancy development. At the same
time, large-scale ascent is increasing here as well. As a result,
we`re seeing a gradual increase in shower/thunderstorm
development across this area. The column is dryer here and mid-
level flow is a bit stronger in advance of the low, so convection
is faster moving with more limited residence time. Main hazard
through the night will be local, brief heavy rainfall leading to
standing water on roadways and urban/poor drainage areas,
especially where slow-moving and training cells exist. Can`t rule
out a very low (10% or less) chance of a flash flood instance
across vulnerable locations of central and southern Utah (slot
canyons, slickrock, normally dry washes) if heavy rain cores
train across a vulnerable area.

Tonight, an upper low is forecast to track eastward across
southern Utah, with the low tracking into Colorado by Saturday
afternoon. As a result, a well-defined TROWAL/deformation zone is
forecast to set up from southern Wyoming south and west across
western Utah (primarily along and west of the terrain), and this
feature is forecast to persist through the morning hours.
Persistent, widespread light to moderate precipitation will
accompany this feature. By afternoon, model consensus suggests
this activity will shift eastward and be located primarily over
the terrain and adjacent valleys of central and northern Utah
while shrinking in size with an attendant diminishing
precipitation rate trend. Snow levels will primarily be in the
7500-8000 foot range, however expect snow levels to fall down to
around 7000 feet in heavier showers. Expecting additional
accumulations across the northern mountains in the 4-8 inch range,
6-12 inches across the central and southern mountains for the
duration of the event. In moist, northwest upslope flow Saturday
night, expect snow showers to persist across favorable terrain of
the central and northern mountains through the night. Saturday morning
appears to be a great time to take care of some indoor chores.

.LONG TERM (After 12Z/6AM Sunday)...Shortwave energy will rotate
into southwest Wyoming and northern Utah Sunday as the main storm
system pushes into the northern plains. Conditions will be drier
throughout, but there will be isolated to scattered rain and
mountain snow showers, specifically for the Bear River Range,
Wasatch, and Uinta Mountains. Mountain snowfall will generally be
less than one inch. Showers will taper off Sunday evening, with
synoptic flow becoming zonal as a trough digs into the PacNW.

There is good model agreement that the trough will dig far enough
south Monday to bring isolated to scattered showers to similar
locations as Sunday. A weak baroclinc zone will track into northern
Utah later Monday, but as the main trough lifts, that front will not
bring much cooler conditions or track all the way through Utah.

Tuesday will be largely dry between the aforementioned trough and
another that some ensemble guidance, roughly 60% of members, have a
similar track for. There is more uncertainty with that, as other
ensemble members have zonal or southwest flow with another trough to
the west. The forecast Wednesday is uncertain with those different
scenarios on precipitation and temperatures. National Blend of
Models 25th to 75th percentile for high temperatures for northern
Utah ranges near 20F with uncertainty on the trough.

Temperatures Sunday will be slightly cooler than normal, increasing
to slightly warmer than normal Monday and Tuesday with more
uncertainty the next day.


&&

.AVIATION...KSLC...Lowering cloud bases and increasing shower
activity will be the name of the game today as a storm system
arrives in Utah. Expecting vicinity showers through a majority of
the day, with the most likely period to see showers impacting the
terminal from 20-01Z. During this time, there is a 30-40% chance of
thunderstorms moving over KSLC. CIGs will remain around 4-5kft AGL
through the day, lowering to around 3kft AGL with passing showers.
Expect variable winds through the morning with light northerlies
prevailing after 15Z.

Rest of Utah and Southwest Wyoming...An active weather day with
widespread showers and isolated to scattered thunderstorms is
expected across Utah and southwest Wyoming during the day today. VFR
conditions will prevail outside of showers with CIGs generally in
the 4-5kft AGL range. Within showers, expect MVFR CIGs. At higher
elevation terminals (e.g. KEVW/ KBCE) expect periods of rain-snow
mix to bring MVFR to IFR due to VIS restrictions.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Winter Weather Advisory until 6 AM MDT Sunday for UTZ111-112.

     Winter Weather Advisory until 6 PM MDT Saturday for UTZ113-117-
     125.

WY...None.
&&

$$

ADeSmet/Wilson/NDeSmet

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