Flood Watch 2, NWS Salt Lake City, UT

Area Forecast Discussion
National Weather Service Salt Lake City UT
355 AM MDT Sat Aug 10 2024

.SYNOPSIS...A monsoon surge continues to bring the threat of heavy
rain to the southern half of Utah, while the northern half of Utah
on the edge of the moisture will see the threat of microbursts
associated with any thunderstorms into the weekend. Conditions
will begin to dry out early next week as the deeper moisture is
shunted east.

&&

.SHORT TERM (Through 12Z Monday)...An ongoing monsoon surge
continues across the region. Early morning upper air and satellite
analysis indicates an elongated ridge across the southwestern
United States. The northern stream remains elevated, though
largely well north of the CWA. Morning mesoanalysis indicates PWs
are 1"+ plus across the lower elevations of southern and eastern
Utah (around 120-150% of normal).

Mean HREF SBCAPE is again in the 500-1000 J/kg range, with
potentially few areas trending a bit higher. Meanwhile, deep layer
shear ranges from 10-15kts near the Arizona border to 25-35 kts
near the Idaho border. These corresponding slow storm motions will
again support the threat of heavy rain, training and down drainage
propagation across southern and eastern Utah this afternoon and
evening. Meanwhile, across northern Utah, the higher shear
environment combined with inverted v profiles and the associated
dry subcloud environment will again support the threat of at least
isolated microburst winds in excess of 50 mph across northern Utah
and Uinta County, WY.

Monsoon moisture will continue to shift north on Sunday and remain
quite elevated across the state. This will bring yet another round
of showers and thunderstorms, with perhaps an increase in the
heavy rain threat across northern Utah.

.LONG TERM (After 12Z Monday)...Long term period begins with
troughing extending through the PacNW while a broad ridge
stretches westward from the Southern Plains. This synoptic pattern
will promote advection of monsoonal moisture into the local
forecast region, with PWAT values somewhere in the 100-150% of
normal range for mid August. Combined with diurnal heating,
guidance suggests this will help lead to widespread
destabilization on the order of around 250-750 J/kg CAPE on
Monday. Along with ~10-30 kts of deep layer shear (especially
further north closer to faster jet flow overhead), afternoon
convective development will likely yield a few stronger and more
organized thunderstorms. The ECMWF Extreme Forecast Index captures
this potential as well, with shading roughly along/north of the
I-70 corridor corresponding to anomalous CAPE- Shear parameter.
While stronger convection will likely wane with loss of daytime
heating through the evening hours, a shortwave pivoting through
the aforementioned trough will maintain precipitation chances
through the overnight hours.

Tuesday and Wednesday will see something of similar patterns in
regards to convective development, though a slight west to east
drying trend through this time will gradually shift highest
precipitation coverage eastward in time. With shortwave energy
continuing to advect through the broad trough, will continue to
maintain sufficient shear to likely yield a few more organized
convective cells during the daytime as well.

Moving into the back half of the work week, synoptic features
become displaced in regards to favorable monsoonal moisture
advection into the region. As a result, will see diurnal
convection become more spatially limited, and generally more
favored over the higher terrain. Progressing into the weekend,
forecast confidence dips as guidance varies in placement of the
ridge anywhere from the Southern Plains westward to the lower
California coast. If it becomes centered from the Southern Plains
to nearer the Four Corners region, then increased moisture tap may
yield increased precipitation potential. Conversely, further
westward positioning would likely maintain drier conditions. For
now, kept NBM guidance which continues with a fairly typical
summertime diurnal convective pattern favoring isolated to
scattered daytime development over high terrain.

In regards to temperatures over the long term period, much of the
forecast region will see afternoon highs near climatological
normal, with a slight uptick in temps on the drier days. Of
course, day to day convection will modulate local temperatures
dependent on exact coverage of precipitation and associated cloud
cover.

&&

.AVIATION...KSLC...Ongoing pattern largely continues with KSLC on
the periphery of monsoonal moisture advection. Southerly winds,
gusty at times, persist through the morning. Low confidence is
then noted on wind direction especially between 20Z-00Z, as any
diurnal flip NW may easily be overcome by increasing convective
outflow potential. To that end, once again will see a chance
(~30-40%) of convection at the terminal, carrying gusty erratic
outflow and lightning threat. VFR conditions largely persist, but
could see brief VIS reduction from any heavier precip or blowing
dust. Convective potential then decreases from late evening into
the overnight, with better confidence on winds settling back
southerly.

.REST OF UTAH AND SOUTHWEST WYOMING...Recent pattern continues as
monsoonal moisture pushes into the region. Convective coverage,
scattered in nature, will be highest at southern terminals from
Saturday afternoon into the evening, with decreasing coverage
expected in northward extent. Convection will be capable of
lightning, gusty and erratic outflow winds, and brief heavy rain
(especially at southern terminals). While VFR conditions will
largely prevail, any heavy precip directly atop a terminal or
blowing dust as a result of outflow winds will have potential to
briefly result in categorical reductions. While some showers will
linger, more widespread convection will begin to wane from the
evening on into the overnight hours. Aside from outflow related
modification, winds will tend to follow something of a typical
diurnal pattern, though with a slight favoring for southerly to
westerly directions during the day.

&&

.FIRE WEATHER...The ongoing monsoon surge will continue to bring
the threat of heavy rain to the southern two thirds of Utah,
while microburst winds will be the main threat for the northern
third of Utah. This pattern will continue through the weekend and
into early next week. Drier air will begin to shift into western
Utah Monday afternoon into Tuesday; western Utah later Tuesday
into Wednesday. A dry, breezy pattern is expected to replace the
monsoon surge, with the gustiest winds across western Utah.

&&

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

Kruse/Warthen

For more information from NOAA's National Weather Service visit...
http://weather.gov/saltlakecity

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