816
FXUS65 KSLC 201027
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
427 AM MDT Mon May 20 2024

.SYNOPSIS...A storm system will bring unsettled conditions to
much of Utah and southwest Wyoming through this evening, and
leave cooler air in place across the region Tuesday. The pattern
will remain active through the remainder of the week, with the
next cold front pushing through the region late Wednesday into
Thursday.


&&

.SHORT TERM (Through 12Z/6AM Wednesday)...An upper trough axis
extends from the northern Rockies of ID/MT southward into the
Great Basin of NV early this morning, with an upper jet located
along the downstream side of this trough from northern Utah into
north central Wyoming. A surface front bisects the forecast area,
extending from roughly Green River to just north of Cedar City.
Showers persist along and just north of this surface boundary
across west central Utah. Most hi-res guidance largely dissipates
this area of showers early this morning, before redeveloping at
least scattered convection in the vicinity of this boundary this
afternoon as it pushes southeast. Any storms developing
immediately along the surface front as it pushes south and east
this afternoon will pose a threat for strong microburst winds as
indicated in CAM guidance. Ahead of the boundary warm, dry and
windy conditions can be expected across areas from the San Rafael
Swell southward into the Grand Staircase. Away from any
convection this afternoon, winds will gust into the 30-40 mph
range with localized areas perhaps approaching advisory criteria
(45 mph).

Meanwhile further north, the entrance region of the upper jet is
interacting with the trailing low level baroclinic zone, resulting
in an area of banded precipitation from the northern Wasatch
Front/Salt Lake County westward to near Ibapah. These mesoscale
bands will persist through the morning, bringing swaths of
precipitation up to 0.25 inches, while areas outside of the bands
will see little if any precipitation. As the upper trough beings
to swing east this afternoon, model guidance focuses the greatest
precipitation coverage across the Wasatch Plateau, western Uintas
and western Uinta Basin with in a region of jet coupling along the
low level baroclinic zone. Snow levels falling below 8000 feet
late today into this evening will result in some accumulation
across the higher elevations before precip winds down.

The upper trough will move east Tuesday leaving a seasonably cool
airmass across the forecast area. Max temperatures Tuesday
afternoon will generally run 6-10F below climo across the
forecast area. Afternoon highs will only reach low to mid 60s
across most valleys of northern, central and southwest Utah, while
temperatures reach the low 80s around St George. Moisture along
the back side of the departing trough will maintain a chance for
showers across northern Utah, mainly along and east of the Wasatch
Crest.


.LONG TERM (After 12Z/6AM Wednesday)...On Wednesday, a broad
longwave trough will extend from the PacNW on into the Midwest, with
the local forecast region sitting beneath largely zonal flow to
maybe very weak shortwave ridging. Through the day, a more marked
and compact shortwave impulse along with a cold frontal boundary
will dig southward from the PacNW. Most guidance suggests this
feature will only begin to impinge upon the northern fringes of the
forecast region by the afternoon/evening, yielding a modest uptick
in isolated to scattered shower activity. The majority of the region
will remain dry, with afternoon high temperatures fairly close to
climatological normal for mid to late May.

Wednesday night on into Thursday, the shortwave will graze the
northern half of the forecast region and push the cold frontal
boundary southward through Utah and southwest Wyoming. Overall,
combination of forcing/moisture doesn`t look all too impressive, and
while a slightly more organized band of precipitation will be
possible along the front, generally just expect isolated to
scattered shower chances to continue to creep southward into central
Utah or so, with the boundary likely stalling somewhere near the I-
70 corridor during the day. Probably the more noticeable impacts
will come in the form of gusty prefrontal winds across southern and
eastern Utah (afternoon gusts ~25-40 mph), and much cooler
temperatures behind the front. To the latter point, afternoon highs
behind the front on Thursday are expected to run about 7 to 15
degrees below normal. Around 80% of ensemble members support some
sort of trailing impulse moving through on Friday, but with the
boundary washing out and limited overall support, mostly anticipate
some isolated afternoon diurnal showers over some of the high
terrain. Additionally, places which saw frontal passage the prior
day will see temperatures rebound several degrees for afternoon
highs as the airmass moderates.

Northern stream remains active moving into the weekend, but some
uncertainty is noted on the exact flow evolution. Similar to the
Thursday system`s progression, another somewhat compact shortwave
trough and associated frontal boundary will dig towards the northern
Rockies from the PacNW. The amplitude of the trough will largely
dictate how far south impacts spread, which is made further
complicated by potential for some weak phasing with the southern
stream (effectively deepening the trough a bit more). As of this
forecast package, around 35% of ensemble members show a deeper
trough or weak phase scenario, with remaining membership depicting a
flatter pattern and more of a grazing system. In both scenarios,
nothing at the moment shows much in the way of substantial
precipitation chances or cold air intrusion, so forecast includes
near to slightly below normal temps Saturday and Sunday along with
some isolated to scattered precipitation generally north of the I-70
corridor.

Deterministic and ensemble guidance show good agreement that Monday
into midweek should see a ridge start to build into the area,
resulting in drier and warmer weather. That said, Memorial Day does
still show a bit of uncertainty with about 20% of ensemble members
keeping some modest lingering influences from the departing trough,
which would allow for maybe some isolated diurnal showers and a
slower warmup. Will want to keep an eye on the forecast for any
outdoor plans, but trend is at least favorable so far.

&&

.AVIATION...KSLC...Trough and associated cold front move through
during TAF cycle. Shower activity will tend to be scattered, though
a more consistent banded feature appears likely somewhere along/near
the front. If this impacts the terminal, most likely window
currently seems to be between ~12-18Z. Generally expect BKN to OVC
VFR cloud cover, but around a 10-20% chance of MVFR conditions
possible in any heavier precipitation. Precipitation chances begin
to decrease and become more isolated Monday evening into the
overnight hours. Winds favored to remain NW, with occasional gusts,
primarily Monday afternoon.

.REST OF UTAH AND SOUTHWEST WYOMING...A system will progress into
the region and push a cold front southward as it does so. For
northern terminals, will see scattered showers continue to develop
as a result, likely along with a band of more consistent showers
along/near the cold front. Largely anticipate conditions to remain
VFR with BKN to OVC CIGS, but around a 10-20% chance of MVFR
conditions will be possible within any heavier precipitation. At
southern terminals, scattered shower/thunderstorm chances increase
by the afternoon, with subsequent frontal passage expected likely by
late Monday evening. For areas behind the front, a more northerly
component to the wind direction is favored.

&&

.FIRE WEATHER...A cold front stretching from roughly Vernal to
Cedar City will remain nearly stationary this morning, before
pushing through southern and eastern Utah this afternoon and
evening. Ahead of this front a warm, very dry (RH less than
15 percent), and windy airmass will reside across areas mainly
east of Highway 89. As this front pushes through these areas
later this afternoon and evening, scattered showers and
thunderstorms accompanied by strong outflow winds can be
expected. Any rainfall with these storms will remain less than
one tenth of an inch.

To the north of the front, a cooler airmass will reside across
northern and west central Utah. As the parent upper level
storm system associated with this front crosses the area,
showers and occasional thunderstorms are expected, with the
greatest coverage across the Wasatch and western Uintas.
With the cooler airmass in place, snow levels will fall
this afternoon and evening allowing for accumulating snow
above 8000 feet. This snowfall will be greatest across the
Uintas.

This cooler airmass will reside across the state Tuesday,
while unstable conditions associated with the passing low
pressure system maintain a chance of showers across the north.
A brief warming trend can be expected Wednesday, before the
next cold front pushes into northern Utah late Wednesday
afternoon and evening, then through the remainder of the
state Wednesday night into Thursday. Any precipitation with
this midweek system will remain confined to northern Utah.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...None.
WY...None.
&&

$$

Seaman/Warthen

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