ut discuss
Office: SLC
FXUS65 KSLC 252201
AFDSLC
Area Forecast Discussion
National Weather Service Salt Lake City UT
401 PM MDT Thu Apr 25 2024
.SYNOPSIS...An active pattern will continue into the weekend,
resulting in valley rain and mountain snow along with a cooling
trend.
&&
.SHORT TERM (Through 12Z/6AM Sunday)...The short term period of
the forecast will be characterized by cool, unsettled conditions
as an area of low pressure moves through the region. As of early
Thursday afternoon, increasing large-scale ascent was acting on
numerous low-level boundaries/cold pools as well as terrain to
force scattered showers and thunderstorms across northern Utah and
SW Wyoming and isolated showers and thunderstorms across southern
Utah. This activity will continue to be capable of producing
gusty outflow winds, frequent lighting and brief, locally heavy
rainfall along with small hail. Deterministic and high-resolution
models are in good agreement with showing a diminishing
precipitation trend through the evening as instability wanes.
However, large-scale ascent and westerly upslope flow will keep
showers going, particularly over/near terrain overnight.
On Friday, a deepening trough across the Great Basin will eject
several shortwaves across Utah and SW Wyoming, resulting in a
gradual development of widespread precipitation. Some of this
precipitation will be briefly, locally heavy. Guidance supports
the highest probability for heaviest precipitation from sunrise
Friday morning through afternoon across northern Utah, with
central Utah favored during the afternoon into early evening and
finally southwest Utah from late morning into the early
afternoon. 24 hour probabilities for 1" or greater QPF is
maximized across northern Utah and SW Utah near the Nevada border,
where these probabilities are in the 40-50 percent range. This
will lead to further rises on area creeks/rivers/streams as long
as standing water on roadways. Ingredients for central and
southern Utah flash flooding are rather marginal, with 300-400J/kg
of SBCAPE, marginal shear and PWATs in the 125-150% of normal
range, though LCLs will be dropping as low-level moisture quality
improves. However, if a cell or group of cells trains across a
vulnerable area, we can't rule out an isolated instance of flash
flooding. Flash flood probabilities, albeit non-zero, are very
low, or 10% or less on Friday.
Late Friday through Saturday, models are in good agreement showing
a closed low tracking from near the UT/AZ border Friday night and
into Colorado through Saturday. This will place all but eastern
Utah within a broad deformation zone, with widespread
precipitation continuing within this region through mid afternoon
Saturday. Snow levels will initially begin in the 8000-8500 foot
range this evening before falling to 7000 to 7500 feet late Friday
night through Saturday, when temperatures areawide will fall to
around 10F below seasonal normals for late April. This will lead
to persistent, widespread snow at high elevations, and as a result
have issued Winter Weather Advisories for the Wastach Mountains
south of I-80 and the Western Uintas, where 25th to 75th snowfall
forecasts are generally in the 8 to 16 inch range for this event.
We can't rule out isolated 12" amounts across the Tushars and
Brian Head as well, but have opted not to include these farther
south mountain zones in a headline at this time given the limited
geographical extent and limited impacts. Should amounts increase
both spatially and in magnitude, may need to consider adding these
areas to the existing Advisories.
.LONG TERM (After 12Z/6AM Sunday)...The second half of the weekend
will be much drier than the first, as the Friday and Saturday storm
system will have become a closed low and have tracked to the east.
Clearing will continue from west to east, although a trailing
shortwave with remnant moisture will allow for convective updrafts,
mainly around higher terrain in the Bear River Range, Wasatch, and
Uinta Mountains. These will be scattered, with isolated to scattered
thunderstorms as well. Minimal rain, or snow above roughly 8000
feet, is forecasted with showers tapering off into the evening.
Temperatures will be around 5-10F warmer than Saturday.
A low amplitude trough will track to the north or graze southwest
Wyoming and northern Utah Monday with zonal flow further south.
There is good agreement from GEFS and EPS members on scattered
showers and isolated thunderstorms, primarily for the mountains of
northern Utah. Rain and snow accumulation will be light, with
showers diminishing later in the day. Temperatures will be roughly 5-
10F warmer than normal.
There will be less shower coverage Tuesday, as flow becomes zonal
for southwest Wyoming and northern Utah with a longwave trough
approaching the PacNW. Dry conditions are likely Wednesday for
southwest Wyoming and northern Utah, as that trough will bring drier
southwest flow. Temperatures will warm to the 70s and 80s for most
valleys, around 15F warmer than normal.
Ensembles are in good agreement that the longwave trough will not
dig into Utah through at least Thursday, so a warm and likely more
windy day is likely. There is more uncertainty later in the week on
the trough and on forcing, cooling, and precipitation that could
push into Utah.
&&
.AVIATION...KSLC...Showers and thunderstorms are expected this
evening with potential for briefly gusty winds and reduced
visibility. VFR conditions are forecast in the near term with
ceilings possibly decreasing to MVFR this evening. A break in
conditions are possible for a few hours tomorrow morning. Ceilings
are then expected to drop again by the afternoon hours under
additional rain showers.
.REST OF UTAH AND SOUTHWEST WYOMING...Scattered showers and
thunderstorms are forecast throughout the evening, bringing the
potential for briefly gusty winds, reduced visibility and lowered
ceilings. Otherwise, VFR conditions will prevail. Continued rain, or
even snow showers for BCE, are forecast overnight and throughout the
day tomorrow. Widespread MVFR to IFR conditions are forecast as a
result. The exception will be SGU where VFR conditions are expected
throughout the period.
&&
.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Winter Weather Advisory from 6 AM Friday to 6 AM MDT Sunday for
UTZ111-112.
WY...None.
&&
$$
ADeSmet/Wilson/NDeSmet
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