754
FXUS65 KSLC 050950
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
350 AM MDT Sun May 5 2024

.SYNOPSIS...Gusty southerly winds will diminish behind
a cold front moving through the state throughout the day.
Valley rain and mountain snow will accompany this front. Most
of this precipitation stays confined to northern Utah. Northern
Utah remains active and colder than normal through Wednesday
morning.

&&

.SHORT TERM (Through 12Z/6AM Tuesday)...A powerful cold front has
moved into northwestern Utah, as of 3am. Temperatures are very
warm ahead of the front with mid to upper 60s stretched across
most Utah valleys with temperatures falling ~20-30 degrees behind
the front. Additionally, there is about a 30-40 degree dewpoint
depression at most pre-frontal weather stations indicating how dry
the lower levels are ahead of the front. This will prevent most
precipitation from reaching the surface until after the front
passes. Even though showers ahead of the front are not resulting
in precipitation reaching the surface, they are acting to enhance
southerly wind gusts up to 60+mph in some locations by mixing down
50kt winds aloft. These brief and isolated gusts will continue
until the front passes.

Frontal passage will occur along the Wasatch Front between 8-10am
with central and southern Utah later this afternoon. Surface winds
will transition to westerly/northwesterly behind the front, but
winds aloft will maintain a southerly component until Sunday
night. This will focus the heaviest precipitation along areas that
do well in southerly flow, but it will also limit precipitation
for northerly facing aspects and valleys that tend to get shadowed
in southerly flow. Hi-res guidance seems to be picking up on this
idea as QPF totals are lower compared to the lower resolution
guidance. But once flow does transition to westerly/northwesterly
overnight Sunday snow will increase in intensity across areas
that do well in this flow regime. Snow will remain off and on
across the terrain of northern Utah through Tuesday morning as
moisture remains in place. The convective potential will be
relatively low for this time of year as instability is meager,
but some isolated convective activity can`t be ruled out. Snow
levels remain mostly unchanged from previous forecasts as areas
below 5000 feet should remain mostly rain with some snow mixing in
along the highest bench locations.

Shortwave ridging will move into northern Utah late Monday and
bring a lull in precipitation overnight Monday. However, a
shortwave will move through Tuesday morning and reinvigorate
precipitation once more in the form of valley rain and mountain
snow. All in all, QPF totals for valley locations of northern Utah
through Tuesday morning will generally be 0.25-0.75" with locally
higher amounts up to 1" across areas that do well in southerly and
westerly flow. Snow totals will be between 8-16" with locally
higher amounts 24"+ across the northern mountains.


.LONG TERM (After 12Z/6AM Tuesday)...At the start of the long term
period of the forecast, model solution space remains locked into the
idea of persistent negative height and temperature anomalies across
the Northern Rockies that challenge records for the time of year,
both aloft and at the surface. The largest surface temperature
anomalies across Utah and SW Wyoming are between Monday afternoon
and Thursday morning, with the highest negative EFI values Wednesday
morning. Digging into the details a bit, a progressive, reinforcing
longwave trough is forecast to be traversing eastward across the
Northern Rockies on Tuesday, maintaining cold, cyclonic flow across
most of Utah and SW Wyoming. As a result, conditions will be
favorable for persistent snow showers across the mountains of
northern Utah. Lake effect probabilities have dropped slightly, and
are now in the 20-30 percent range from just after midnight Tuesday
morning through midday Tuesday. Nonetheless, the ingredients are in
place to once again support lake effect/lake enhanced activity. With
W-WNW flow in place through the boundary layer, locations from Ogden
to Bountiful and perhaps as far south as North Salt Lake will be
favored for lake enhanced activity. Another lobe of vorticity will
drop down the backside of the impressive longwave trough, acting to
once again reinforce the negative height anomalies across Utah and
SW Wyoming on Wednesday. This will mean a third morning of enhanced
lake effect/enhancement probabilities Wednesday morning. Unlike
Tuesday morning, boundary flow trajectory is more out of the NW,
favoring locations from Bountiful to SLC. Going back a day, wanted
to mention that lake-induced CAPE values on Tuesday are impressive,
reaching nearly 1400J/kg with equilibrium heights up to 18,000 feet.
Given this, it`s not out of the question that some lake
effect/enhanced activity could contain lightning.

Additional snow accumulations in the 48 hrs preceding 12Z Thursday
morning are in the 6-12 inch range across Utah`s northern mountains,
with locally higher amounts in the Logan and Ogden area mountains as
well as the Upper Cottonwoods. During the overnight and early
morning hours, snow levels will be cold enough to support snow down
to valley floors, and locations away from the Great Salt Lake
shoreline (with its moderating influence on sfc and boundary layer
temperatures) could see anywhere from a trace (25th percentile) to a
few tenths of an inch of snow (75th percentile). It`s worth noting
that the 95th percentile values paint 1-3 inches across the Northern
Wastach Front with 4 inch amounts over benches, representing a low
probability outcome.

Temperatures will be some 10F to 20F below normal through Wednesday
for highs. The coldest morning appears to be Wednesday morning, with
widespread 20s forecast for many western, eastern and central Utah
valleys, including the Tooele and Rush Valleys. We`re currently
forecasting temperatures near 32F in Eastern Box Elder County, the
Cache, and outlying areas of the Wasatch Front. Folks will once
again need to take steps to protect tender/sensitive vegetation.

Ensembles are in good agreement in depicting gradually rising
mid/upper level heights from Thursday through next weekend. At the
surface, we see gradually warming temperatures during this period,
with temperatures rising to near to slightly above normal by next
Sunday. What`s interesting is that the Canadian and GFS global,
deterministic solutions continue to latch onto the idea of
maintaining low pressure across the Great Basin through next
weekend, maintaining cooler, unsettled conditions, but not as cool
as what we are in line to experience early this week. This unsettled
pattern has representation from about 25% of the solution space.
While the most likely scenario supports warming, dry conditions, do
know that about 1/4 of the solution space suggests we`ll hold onto
unsettled conditions. Stay tuned to see how this trend evolves over
the next few days.

&&

.AVIATION...KSLC...Active period as a winter-like storm will be in
place through midweek. Strong, gusty S winds to around 40kt will
continue through about 14Z. Incoming cold front will begin to cause
a wind shift to the SW around 14Z and then to the W-NW by 15Z and
finally NW by 18Z with gradually decreasing speeds. Winds off the
surface, mainly above 2kft, remain S-SW until late afternoon,
possibly resulting in some LLWS. By late morning, shower chances
become increasingly likely ahead of cold front, though strong south
flow may initially yield some downsloping off terrain, abating
precip to an extent. Widespread precip will develop after the
frontal passage by early afternoon with MVFR conditions fairly
likely during times of heavier precip, with periods of IFR possible
(with nearly a 20% chance.) Trailing wave will bring an uptick in
precipitation tonight, with temperatures cold enough to allow snow
to mix in at times.

.REST OF UTAH AND SOUTHWEST WYOMING...An anomalous winter-like
system will be in place across the region through early week,
resulting in active TAF period along with persistent periods of
mountain obscuration, especially across northern Utah. Strong
southerly winds will precede a cold front as it marches eastward
across Utah today, exiting into Colorado this evening. Showers ahead
of the front will aid in mixing, with occasional gusts to 50kts
reaching the surface at times. Precipitation chances become further
elevated through the morning and afternoon as cold frontal boundary
moves through. MVFR conditions likely in heavier precip, with IFR
possible at higher elevation terminals where snow may mix in, with
the best chance of this across SW Wyoming. Strongest winds/gusts
will begin to subside following the frontal passage, with directions
largely trending more west to northwesterly. Periods of rain and
snow showers then persist across northern Utah and SW Wyoming into
Monday morning.

&&

.FIRE WEATHER...Unseasonably cold conditions will be
in place across the area through midweek, especially across
northern Utah. Significant snow for the time of year will fall
across northern Utah`s mountains. A warming and drying trend will
then commence by Thursday, with gradual warming and drying expected
to continue into next weekend. Isolated showers may persist through
the end of the week, especially over northern Utah terrain. Much
lighter winds will be in place across the area from Wednesday through
next weekend.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Wind Advisory until 6 AM MDT early this morning for UTZ101-102-
     105-122.

     Winter Storm Warning from 6 AM this morning to noon MDT Tuesday
     for UTZ110>112.

     Wind Advisory from 6 AM this morning to 10 PM MDT this evening
     for UTZ114-120-121-126>131.

     High Wind Warning until noon MDT today for UTZ115.

WY...None.
&&

$$

SHORT TERM...Mahan
LONG TERM...A. DeSmet
AVIATION...A. DeSmet
FIRE WEATHER...A. DeSmet

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