729
FXUS65 KSLC 131032
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
432 AM MDT Sat Jul 13 2024

.SYNOPSIS...A strong area of high pressure will continue to bring
very hot and dry conditions to the region through Saturday.
Moisture will continue to spread into southern Utah over the
weekend, and then increase across the region by early next week,
bringing with it some shower and thunderstorm activity. The ridge
is then expected to build back across the region

&&

.SHORT TERM (Through 12Z/6AM Monday)...Early Saturday morning, the
center of a persistent ridge of high pressure was located over
extreme southeast Utah. Per model consensus, the ridge will
continue to drift ever so slowly eastward and be centered over
southern Colorado on Sunday while simultaneously weakening. The
net effect on our sensible weather will be two-fold, with both a
slight cooling trend and an increase in moisture across Utah and
SW Wyoming as a result of the ridge`s evolution. With the ridge
moving off to the east, modest deep-layer southeast flow will
trend southerly and finally southwesterly as we head through the
weekend. As a result, total column moisture will steadily
increase through the weekend, with PWATs topping out in the
150-175% of normal range across all but extreme SE Utah by late
Sunday.

Due to the presence of increased moisture, we`ll witness a steady
uptick in shower and thunderstorm activity, especially during the
peak heating hours of the afternoon and early evening hours.
Today, showers and thunderstorms will develop over high-terrain
areas and then generally drift off to the north and west, although
weak flow suggests plenty of opportunity for erratic movement.
With modest SBCAPE and deep-layer shear developing this afternoon,
a few storms may show some organization and longevity. CAMs
continue to favor the idea that a convective cluster will develop
over northern Arizona this afternoon and drift northwestward, with
the cold pool from this activity eventually merging with an
existing cold pool across Iron and Millard counties, resulting in
additional shower/thunderstorm development. This appears to be
the most favored area for briefly heavy rainfall this
afternoon/early evening. However, we can`t rule out briefly heavy
rain and an isolated flash flood threat across other flood-prone
areas of southern Utah however, namely normally dry washes, slot
canyons and slickrock areas. Primary threat, however, will be
gusty outflow winds as any shower/storm will carry the potential
of producing gusts in the 35-45 mph range, with a 10% chance for
isolated gusts to 60 mph.

Farther north, there is a bit more uncertainty regarding shower
and thunderstorm coverage, especially for valley areas. Most NWP
members develop some convection over terrain, but not all allow
convection to propagate to nearby valleys. Do see a scenario
where a shower or storm develops over the Oquirrhs and moves
across the southern half of the Salt Lake Valley this afternoon,
as one example of a valley location that has a slightly higher
opportunity of occurrence, with odds around 20%. There is some
potential for a remnant, convective-induced lobe of vorticity to
track across northern Utah and SW Wyoming late tonight and Sunday
morning, which may allow for some additional nocturnal shower and
thunderstorm activity across these areas. Convection aside,
another extremely hot day remains on tap across the area today,
with highs surging into the 90s and 100s for many valley
locations. Probabilities for reaching 107F at SLC remain around
35%, but will ultimately be determined by how much cloud cover
develops across nearby terrain, strength of southerly downslope
winds this morning and strength of the lake-induced shallow cold
pool.

.LONG TERM (After 12Z/6AM Monday)...At the start of the long-
term period on Monday, the ridge of high pressure that brought
record- breaking temperatures to our area will have shifted
eastward, providing some relief from the heat, especially as the
ridge weakens a bit on Monday. With this weakening/flattening of
the ridge, this will allow some drier air to filter in from the
west. However, mid- level moisture is still expected to hang
around through at least Day 7, providing daily chances for showers
and thunderstorms especially across southern areas and across
higher terrain. The low levels will remain fairly dry, deterring
flash flood chances unless storms are able to train or back-build.
Gusty and erratic outflow winds will continue to be a threat near
any developing showers. It`s worth noting that portions of
northern UT (such as the Wasatch Front) may remain quite dry
during this time, with only increasing cloud cover during the
afternoons.

Heading into mid-week, the ridge will regress and begin to build
once again right over Utah. This will likely bring a slight increase
in temperatures, though current guidance isn`t suggesting a heatwave
like this past week. Moisture will increase once again heading
towards the weekend, with increasing coverage of showers and
thunderstorms across much of the area.

&&

.AVIATION...KSLC...Southerly winds will transition to northwesterly
around 18-19z. A few isolated showers are possible across the Salt
Lake Valley after 21z, with the main impact being gusty and erratic
outflow winds around 20-30kts and a 10% chance of thunder. Showers
may linger as late as 06z. High density altitude will again be a
concern given hot temperatures this afternoon.

.REST OF UTAH AND SOUTHWEST WYOMING...Isolated to scattered showers
and thunderstorms will develop after ~19z across much of the area,
with higher coverage over higher terrain. These showers will be
capable of producing gusty and erratic outflow winds to 30-40kts
(10% chance of up to 50kts). Otherwise, largely diurnally-driven
winds are expected. Smoke could produce lower VIS near local
wildfires. High density altitude will again be a concern give hot
temperatures this afternoon.

&&

.FIRE WEATHER...Hot temperatures continue across the area through
Saturday before trending slightly cooler by Sunday with the
slightly cooler trend continuing into early next week. Midlevel
moisture has started to increase into the area and will
continue through the weekend into early next week as the high
pressure center gradually shifts slightly east closer to the Four
Corners. The coverage of high-based showers and thunderstorms will
continue to increase Saturday, with widely scattered dry
thunderstorms across roughly the southwestern quadrant of Utah.
Some of these thunderstorms will gradually trend wetter throughout
the day, but given the threat of dry thunderstorms initially,
along with the recent prolonged hot and dry conditions, Red Flag
Warnings have been issued. Given the dry conditions, any
thunderstorm will be capable of producing gusty and erratic
outflow winds, with gusts in the 35-45 mph quite common, however
there is roughly a 10 percent chance that isolated gusts could
reach 60 mph. By Sunday, thunderstorm coverage is expected to
increase across the north, and many of these storms will likely be
dry. Southern Utah will see increasing chance of wet
thunderstorms on Sunday (though still mixing with a few dry
thunderstorms). The moisture is expected to linger through much of
next week, with daily convection expected with a mix of wet and
dry thunderstorms. Best chances for showers and thunderstorms will
gradually shift to southern Utah by the middle and later portion
of next week.

With the increase in moisture through early next week, a modest
increase in humidity is expected, especially for any areas that
receive wetting rains. Temperatures will climb a couple of degrees
once again late next week as the ridge, in a slightly weakened
state, moves back directly overhead.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Excessive Heat Warning until midnight MDT tonight for UTZ101>107-
     114>116-118>124-128>131.

     Red Flag Warning from noon today to 10 PM MDT this evening for
     UTZ492-493-495>498.

WY...None.
&&

$$

ADeSmet/Cunningham

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