199
FXUS65 KSLC 202210
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
410 PM MDT Mon May 20 2024

.SYNOPSIS...Cooler, more stable conditions will exist across much
of the forecast area on Tuesday as a trough begins lifting out of
the region. A brief warm period is anticipated in the return flow
on Wednesday, however, active weather returns shortly thereafter,
bringing cooler conditions and a chance for showers across
northern Utah and southwest Wyoming through the first half of the
weekend.

&&

.SHORT TERM (Through 12Z/6AM Wednesday)...An upper trough
continues to progress through the region this afternoon, bringing
an area of showers and isolated thunderstorms focused along the
associated cold frontal boundary. Areas of showers behind the
frontal boundary remain active, largely due to an upper diffluent
region across northern Utah. Much of the shower activity of the
day up until this point has been tied to the western half of the
forecast area (i.e. where the front has progressed). Meanwhile,
the eastern half of Utah has remained very dry at the surface
(relative humidity less than 10-15%) and windy.

Tonight, the front continues to move through the southern and
eastern portions of the forecast area, helping to keep showers
invigorated overnight. Minimal impacts are expected from these
showers, however, as isolated thunderstorm will be possible
overnight in southern Utah.

Colder, more stable air will be draped over much of the forecast
area tomorrow, helping to bring cooler and drier conditions
throughout. That said, trailing disturbances in the wake of the
trough axis will keep at least isolated to scattered showers in
the forecast across northeastern Utah and southwest Wyoming.
Again, very little impacts are expected from these showers.
Temperature-wise, will see much cooler temperatures (10-15 degrees
below normal) across the area as a whole tomorrow, with the most
significant cooling anticipated across southern and eastern Utah
(i.e. areas where the front has not yet progressed as of 1600 MDT
Monday).

.LONG TERM (After 12Z/6AM Wednesday), Issued 427 AM MDT...
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...Northwest winds expected to hold through the
majority of the TAF period, with only a period of light and variable
winds within the 10-13z window Monday morning. Shower chances
increase with isolated potential after 03z this evening, trending
scattered and more consistent than not after 16z. Gusty and erratic
outflow possible with showers, most likely on Monday. VFR conditions
are expected to be maintained with cigs anticipated to remain above
7kft.

.REST OF UTAH AND SOUTHWEST WYOMING...A boundary across central
Utah will continue to be the focus of high based showers through
this evening. Some gusty and erratic outflow winds will be possible
near these showers. Areal coverage of showers will increase across
northern Utah and southwest Wyoming after 10z coincident with the
next storm system. At this time anticipating VFR conditions, though
brief reductions are possible in SW Wyoming within a rain/snow mix
Monday, as well as mountain obscuration of northern Utah mountains.

&&

.FIRE WEATHER...A cold front progressing through Utah today has brought much cooler
and wetter conditions across the western half of the state while
the eastern half of the area remains under critical fire weather
conditions. The cooler airmass will spread over the remainder of
the area through the overnight hours, bringing cooler temperatures
to eastern Utah. While only minor moistening of the eastern Utah
valleys is expected on Tuesday, the western half of the area will
see significant drying.

Warm southerly return flow spreads over the region through
Wednesday, bringing a warming and drying trend to the area.
Another day of hot, dry, and breezy conditions is expected across
mainly the western half of Utah while the eastern half sees more
isolated critical fire weather conditions. Another trough looks to
drop into the region Wednesday night through Thursday, which will
act to at least moderate fire weather conditions through the
early weekend. Much of Thursday and Friday will be mostly dry with
increasing chances of precipitation on Saturday.

&&

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

&&

$$

SHORT TERM...Webber
LONG TERM...Warthen
AVIATION...Cunningham

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