733
FXUS65 KSLC 060955
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
355 AM MDT Mon May 6 2024

.SYNOPSIS...A cold, unsettled pattern will continue through
midweek across much of the region...bringing significant northern
mountain snow accumulations. A gradual warming and drying trend is
expected across northern Utah late in the week. This warm-up may
be slower across southern Utah as a remnant low remains in place
across the area.

&&

.SHORT TERM (Through 12Z/6AM Wednesday)...An unseasonably cold,
elongated upper low continues to progress east across the northern
Utah/southwest Wyoming early this morning. A fairly broad area of
precipitation across northern Utah is being driven in large part
by the upper circulation passing overhead, with some orographic
enhancement and perhaps a little influence from the relatively
warm waters of the GSL as -8C to -9C 700mb air spreads overhead.
Snow levels are generally just off the valley floor, but are
falling within heavier showers/bands of precipitation.

This area of forcing will move east through sunrise, however
quickly on its heels is a plume of low/mid level warm advection
spreading across southern Idaho and far northwest Utah, on the
back side of the parent low. This region of forcing will spread
across northern Utah/southwest Wyoming this morning, bringing
another round of organized precipitation. Valley floors will again
see a mixture of rain and snow dependent on precip rates, while
elevations above roughly 4500 feet see predominant snow. This snow
will be heavy at times across the higher terrain of northern
Utah, where a Winter Storm Warning remains in effect.
Precipitation will trend showery this afternoon as shortwave
ridging temporarily builds overhead.

Temperatures will remain well below climo across the forecast area
today, with max temps remaining confined to the low-mid 50s
across the northern valleys (10-15 degrees below climo), and low
70s around St George and Bullfrog.

Late tonight into Tuesday an upstream shortwave trough will
quickly dig into the region bringing another round of
precipitation to the I-15 corridor and adjacent terrain across
northern and central Utah. Snow levels will again flirt with the
valley floors, with accumulating snowfall persisting across the
higher terrain. Current Winter Storm Warning expires midday
Tuesday, and may need to be extended depending on whether the
snowfall Tuesday remains impactful. The re-enforcing shot of cold
air will also trend temperatures 5F or so cooler over northern
Utah Tuesday, where max temps will remain in the mid to upper 40s.
Meanwhile temperatures across southern Utah will trend 2-5F
warmer. With this colder air mass spreading into the region, the
potential for a hard freeze exists late Tuesday night across at
least outlying portions of the Wasatch Front and may require
headlines.

.LONG TERM (After 12Z/6AM Wednesday)...Our active pattern over the
next few days will start to subside as the trough responsible for
the unsettled weather will become positively tilted across the
Rockies on Wednesday. Given that a light northwest flow will remain
in place Wednesday morning along with some moisture advection from
the north, lake effect snow is still a possibility (~30% chance) to
the south and east of the GSL. Otherwise, the synoptic forcing
begins to deteriorate with relatively drier conditions unfolding.
Temperatures will remain 15-20 degrees below normal across northern
Utah and ~10 degrees below normal for southern Utah.

As this positively tilted trough lingers across the Rockies on
Thursday and a ridge builds into the PNW, flow aloft will gradually
become more easterly. Flow aloft looks to remain light with cold air
advection fairly marginal resulting in a limited potential for
enhanced easterly canyon/downsloping winds across northern Utah, but
these parameters will be worth monitoring to see if future guidance
starts to trend towards a more impactful scenario.

Guidance has trended towards a scenario in which the parent trough
shifts to the east, but a cutoff low develops across the Great Basin
over the weekend (~87% of members). This weak cutoff low would keep
low PoPs across the area through the weekend with a gradual warming
trend, whereas a more prominent ridge nosing in from the PNW would
lead to much drier and warmer conditions. Additionally, with the
cyclonic flow centered over the southern Great Basin and anticyclonic
flow to our northwest, easterly winds aloft would continue. As
stated previously, the strength of enhanced canyon/downsloping wind
parameters will be monitored closely.

This low looks to gradually decay by early next week with 80% of
members indicating a quieter pattern as ridging spreads into the
Great Basin from the PNW.

&&

.AVIATION...KSLC...MVFR conditions will persist across the KSLC
terminal through midday as light rain and snow continue with reduced
CIGs and mountain obscuration. Two main rounds of precipitation will
move through the terminal. The first, already ongoing, will move out
by ~10Z with another arriving ~13Z and lasting through ~20Z.
Conditions improve to VFR after the second round of precipitation
with VCSH continuing through the afternoon. Light and variable winds
will transition to a gusty west/northwesterly wind during the day.

.REST OF UTAH AND SOUTHWEST WYOMING...MVFR/IFR conditions across
northern Utah/SW Wyoming will persist through midday as light rain
and snow reduce CIGs and VIS, at times. Southern Utah will dry out
with a few snow showers exiting the high terrain and VFR conditions
developing and remaining throughout the day. Winds will become gusty
out of the west/northwest and persist throughout the day.


&&

.FIRE WEATHER...An unseasonably cold storm system will continue
to bring periods of accumulating mountain snow and low elevation
rain across northern and central Utah today through Tuesday. Any
precipitation across southern Utah will remain more spotty.
Temperatures across northern Utah will run 10 to 15 degrees below
normal today and again Tuesday, while temperatures across southern
Utah remain 6 to 10 degrees below normal. With these cool and
unsettled conditions, daytime relative humidity will remain
elevated with excellent overnight recovery.

A shift toward warmer and drier conditions is expected beginning
late this week, however a fair amount of uncertainty remains
regarding how quickly this trend will become established. Roughly
half the guidance begins building a strong area of high pressure
with a more robust warmup heading into the weekend, while the
other half maintains a weakening low pressure area across the
region resulting in a slower warm-up.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Winter Storm Warning until noon MDT Tuesday for UTZ110>112.

WY...None.
&&

$$

Seaman/Mahan

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