622
FXUS65 KSLC 031035
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
435 AM MDT Fri May 3 2024

.SYNOPSIS...An approaching storm system will bring much warmer
conditions Saturday with strong afternoon winds for portions of
Utah. A cold front will track into Utah Sunday. Lighter winds,
cooler conditions, valley rain, and mountain snow are likely once
the front pushes through.

&&

.SHORT TERM (Through 12Z Monday)...A grazing shortwave with a weak
cold front has brought showers, snow above roughly 6000 feet to
southwest Wyoming and northern Utah. Drier conditions will build
in through the morning from west to east as the trough axis will
push downstream. Shortwave ridging will build in Friday night
into Saturday, with a clear, chilly night into Saturday.

Strong warm air advection will push valley temperatures into the
70s and 80s as a longwave trough with a closed low track into the
PacNW. As it digs southeast, flow aloft will increase through the
day. With very dry conditions and strong lapse rates, that flow
will be efficient to mix. The strongest winds will not be until
later Saturday afternoon, through the overnight, and into Sunday.
The main uncertainty is with valley winds during the overnight
Saturday into Sunday. That is when there is good agreement on the
strongest winds aloft, with more than 50 knots at 700 mb. While
conditions will be dry, increasing cloud cover and timing will
work against efficient mixing. That could allow for surface winds
to stay steady or decrease slightly. The most confidence for winds
to hit at least advisory criteria is for southwest Utah,
specifically for portions of Iron, Beaver, and Millard counties,
including Cedar City, Delta, and Milford. Models have almost 100%
probabilities gusts of more than 45 mph Saturday afternoon into
Sunday, with more than 50% confidence for winds exceeding High
Wind Warning speeds. There is lower confidence in places like
lower Washington County and Zion National Park that often don`t
get as windy as guidance with southwest flow. High-resolution
guidance will give more confidence.

Winds will drop off for those locations as a baroclinc zone
pushes into Utah Sunday. There are differences in timing of
several hours, but high confidence in the front pushing into
western Utah during the morning and into the urban corridor late
morning or early afternoon. Strong cold air advection, forcing,
and a transition to northwest winds will come with the boundary.
There is a low, roughly 15% chance for thunderstorms near the
boundary. Snow levels will drop from roughly 9000 feet to
5000-5500 feet after the front pushes through. The northern Utah
mountains will get the most precipitation, with most of that
behind the front with upslope orographic enhancement. Snow water
equivalent of 1-2 inches is likely, locally higher in the upper
Cottonwoods and Ogden area mountains. There will be a range of
snowfall for the mountains, with generally 6-12 inches, but
locally around 24 inches for those aforementioned locations. Many
northern valleys will get around 1 inch rainfall from Sunday and
Monday.

For far southern and eastern portions of Utah, Sunday will be a
windy day in the warm sector, with similar wind speeds and gusts
as western Utah. The front will push through there Sunday into
Monday. Precipitation will generally be lower further southeast.

.LONG TERM (After 12Z Monday)...A common theme appears to be in
store for the bulk of the long term portion of the forecast, and
that is a continuation of cool, unsettled conditions. Kicking things
off on Monday, model solution space is in universal agreement in
their depictions of negative height anomalies in place across the
PacNW and Northern Rockies, courtesy of the presence of a broad
longwave trough. Closer to home, northern Utah will reside within
broad cyclonic flow in the wake of a departing low and cold front,
and this will maintain showery conditions across northern valleys
with snow showers in the mountains. Monday morning, snow levels drop
down to as low as 5000-5500 feet, low enough to support snow on
benches. If we peer into the realm of the low outcome probability
spectrum, we do indeed see 90th percentile/10% probability snowfall
amounts of a few tenths of an inch to as high as 1-2 inches on
benches. In the northern and central mountains, there is a high
probability of snow showers persisting through the day. As you might
imagine, temperatures will be well below early May normals Monday,
checking in some 10F to 20F below seasonal normals. Brrr.

By Tuesday, slight temperature moderation is seen across extreme
southern Utah while central and northern Utah see steady state
temperatures and a smattering of valley rain and mountain snow
showers. We once again cannot rule out snow showers down to benches
Monday night Tuesday morning. Surely, lake effect snow cannot happen
in May, right? Lake effect snow probabilities suggest that yes, it
indeed could. Local lake effect snow probability output reaches as
high as 40% Sunday night, 30% Monday morning and 20-30% Tuesday
morning. An early look at lake effect snow parameters do suggest the
ingredients are in place (sufficient lake sfc to 700mb delta Ts,
favorable fetch, steep low to mid level lapse rates and sufficient
moisture in the DGZ). How much this could contribute to totals is
uncertain at this time and will require further analysis and
refinement particularly as we get into the high-resolution horizon,
generally within 48 hrs.

As we nudge time into the midweek portion of the forecast, we see a
continuation of cool, northerly flow trajectories across the region
with an easing of the cyclonic flow regime thanks to the gradual
weakening/departing trough. Deterministic and ensemble solutions are
in good agreement through Thursday in their depictions of this
evolution. For you and me living here at the surface, this
translates to a continuation of cool, albeit moderating conditions
through midweek, although we can`t rule out diurnally-driven showers
through Thursday, particularly over terrain features of northern
Utah. We do begin to see the emergence of some divergence in the
solution space by Friday, with approximately 1/3 of the solutions
hanging onto negative height anomalies while the remainder of the
ensembles are more progressive with a ridge nudging into the area.
If the troughy scenario plays out, expect temperatures to remain 0F-
10F below normals by Friday, while the other camp of solutions
suggests temperatures warming back to normal and perhaps slightly
above by Friday.

&&

.AVIATION...KSLC...Scattered to broken ceilings will last through
the morning. Clouds will diminish through the afternoon. Light
northwest winds will last through the day.

.REST OF UTAH AND SOUTHWEST WYOMING...MVFR or lower ceilings are
likely for southwest Wyoming and portions of northern Utah most of
the morning. Clouds will diminish through through the day there,
with mostly clear conditions elsewhere. Light northwest winds will
last through the day for southwest Wyoming and most of Utah.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...High Wind Watch from Saturday afternoon through Sunday morning
     for UTZ115-122.

WY...None.

&&

$$

SHORT TERM...Wilson
LONG TERM...ADeSmet
AVIATION...Wilson

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