570
FXUS65 KSLC 192215
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
415 PM MDT Wed Jun 19 2024

.SYNOPSIS...Temperatures will trend warmer across the area through
Thursday before anomalous moisture spreads into eastern Utah late
Thursday through Friday, bringing showers and thunderstorms with
locally heavy rainfall and an associated flash flood risk. Drier
conditions are expected over the weekend and into early next week
with hot temperatures.

&&

.SHORT TERM (THROUGH 12Z SATURDAY)...Utah remains under a fairly
dry and increasingly warm southwesterly flow aloft this
afternoon, downstream of a diffuse trough currently sitting over
the West Coast. Aside from some increasing cloud cover, generally
quiet conditions will continue into the overnight hours. However,
this is just the quiet before the storm.

Tomorrow, moisture will start to increase from the southeast,
with contributions from Tropical Storm Alberto over the Gulf of
Mexico. Initially, midlevel moisture will spread into the area
tomorrow afternoon, with PWATs increasing to over 1 inch across
the southeastern portions of the forecast area by 00z Friday.
Deeper moisture will then work its way in tomorrow night through
Friday, with PWATs peaking at over 1.25 inches, mainly across
southern/eastern Utah. This is anomalous for this time of year,
and ensemble mean IVTs are above the 99th percentile (although
keep in mind that this is typically one of our driest times of
the year).

Generally, what can be expected with this pattern would be an
initial round of high-based showers and thunderstorms tomorrow
afternoon across southeast Utah given inverted-V profiles in
model soundings. Latest CAMS show this activity to be fairly
isolated. However, there is a potential for strong microburst
winds, with a majority of HREF members showing an outflow boundary
with 50-60+ mph gusts across the eastern Grand Staircase and Glen
Canyon. With the arrival of deeper moisture, expect a transition
to a greater potential for measurable rain as showers continue
through the night (this supported by large-scale dynamics as the
upstream trough weakens and ejects across Utah in several pieces).
Then, locally heavy rain will become more likely by Friday
afternoon. Additionally, there should be sufficient shear to
maintain a few organized storms, and latest CAMS are showing
increased coverage of stronger storms with 40-50+ dBZ of simulated
reflectivity from around the spine of Utah through the eastern
valleys beginning late Friday morning. However, there is a
potential limiting factor against strong convection on Friday, and
that would be cloud cover. If enough clouds from Thursday
night/Friday morning remain in place into the afternoon peak
heating period, that could limit solar insolation and reduce the
chances of strong convection. Nevertheless, something to watch, as
any decent convection could pose problems in the many flash-flood
prone areas across eastern Utah, including slot canyons, dry
washes, and burn scars.

.LONG TERM (After 12z/6AM Saturday), Issued 423 AM MDT...
Heading through the weekend models maintain solid agreement on an
area of high pressure building back into the forecast area. This
area of high pressure will allow temperatures to rise back up to
around 10-15 degrees above normal across the area, especially
across the northern half of the area. This will be record
challenging heat. For example, the high temperature forecast for
SLC on Sunday, June 23 is 100 degrees while the record for the day
stands at 101 degrees (set back in 2012). In addition to the
daytime heat, overnight lows will remain fairly elevated in the
low- to mid-70s, particularly across urbanized areas of northern
Utah. For southern Utah, particularly lower Washington County,
lows may not even drop below 80 degrees. The combination of the
high daytime temperatures and minimal relief during the overnight
hours raises concerns for those who are sensitive to heat and
those with insufficient cooling methods. Will need to continue to
assess the need for heat related headlines through at least Monday
as this is the period where temperatures will be highest.

Precipitation-wise, much of the northern half of the area will
remain dry under the influence of the high, however, moisture will
linger over the southern half of Utah and bring a chance for showers
and thunderstorms through at least Monday. Ensemble guidance from
the EPS and GEFS still shows precipitable water values of upwards of
175-225% of normal along roughly the southern half of Utah. There is
still some uncertainty revolving around how far north this moisture
will creep, which is dependent on how much an active northern jet
stream will suppress the high early in the week. Nonetheless, should
still see at least isolated to scattered showers and thunderstorms
over southern Utah late in the weekend/ early in the work week.
Higher than normal PWAT values will bring increased concern for
flash flooding in the typical problem areas. Will need to see how
models trend through the week... but the potential is there.

&&

.AVIATION...KSLC...Northwest winds will transition to southeast
around 05Z. Mostly cloudy conditions will last through around 15Z
with mostly clear conditions much of the day. There is uncertainty
on timing of northwest winds, with a transition likely around likely
around 19-21Z.

.REST OF UTAH AND SOUTHWEST WYOMING...Mostly cloudy conditions are
likely throughout southwest Wyoming and northern Utah, with clear
conditions throughout southern Utah through the overnight and
morning. Southwest winds will gust around 25 knots from 18-03Z
throughout southern and eastern Utah. Isolated to scattered showers
and thunderstorms capable of gusty, erratic outflow winds are likely
for portions of southeast and east Utah from 21-06Z.

&&

.FIRE WEATHER...Warm and dry conditions will give way to increasing
moisture spreading into southern/eastern Utah by later in the day
Thursday through Friday. Initially, midlevel moisture will bring
the threat of isolated dry lightning tomorrow afternoon across
south-central through southeast Utah, along with isolated strong
microbursts potentially in excess of 50 mph. Additionally, minimum
relative humidities tomorrow will remain on the low side at least
through the early part of the afternoon. This, combined with
general southerly winds gusting to around 30 mph will bring
isolated or borderline critical fire weather conditions to
portions of south-central Utah where fuels have cured.

As the moisture becomes deeper Thursday night into Friday, showers
and thunderstorms will increase, with the threat gradually
transitioning from dry lightning and microbursts to locally heavy
rain, still primarily focusing on southern/eastern Utah.
Thereafter, the airmass will trend a bit drier, but lingering
low-level moisture may maintain at least isolated thunderstorms
through the weekend.

Temperatures will trend cooler across eastern Utah for Friday in
conjunction with the deeper moisture, then rebound for the weekend
and becoming very hot again Sunday into the early part of next
week.

&&

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

$$

Cheng/Webber/Wilson

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