Special Weather Statement, NWS Salt Lake City, UT

Area Forecast Discussion
National Weather Service Salt Lake City UT
339 PM MDT Fri Aug 9 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 by Monday as the deeper moisture is shunted
east.

&&

.SHORT TERM (Through 12z Sunday)...Afternoon satellite and H5
analysis place the local region on the northwestern periphery of
broad high pressure extending from the southern plains west across
the desert southwest. The western periphery of monsoonal moisture
about the high appears oriented over central Nevada...with a
notable downtick in PWAT extending further west into western
Nevada attm. From Washington County northwest across this gradient
noting PWAT values decrease from 1.1" to roughly .50" indicating
the strong moisture gradient. This region is one focus for
convection that will continue to spread into western/northern Utah
through this evening, with diurnal initiation being somewhat
aided by subtle stream-wise vorticity within near westerly flow.
The other area of convective initiation today has been over the
central/southern mtns and driven by namely diurnal
destabilization over the elevated heat sources.

For western and northern Utah steep lapse in place will allow for
moderately strong updraft formation through the peak heating hours
today, while dry low levels/high LCL's will drive DCAPE values to
1500-1700 J/Kg...this owing to elevated microburst potential, and
at the least gusty outflow boundaries (in time). Central and
southern Utah however remain locked in the more primed monsoonal
airmass supporting local heavy rain potential. Two different
areas, and a tale of two different storm modes.

Minimal change is expected in the big picture regarding high
placement and breadth of moisture over the next 24 hours...although
consensus is for a slight easterly shift of the aforementioned
moisture gradient into eastern Nevada. CAMs suggesting similar
convective initiation, just a skosh further downstream and over
western Utah vs. eastern Nevada (like today). Anticipating similar
storm modes as well...greater wind potential across the northern
half of the area Saturday, and better potential for locally heavy
rainers across the south.

.LONG TERM (After 12z Sunday), Issued 434 AM MDT... A series of
shortwaves Sunday-Tuesday will interact with anomalously high
PWATs that are being advected in from moist southwesterly flow
along the western periphery of a ridge centered over west Texas.
This will result in daily convection each afternoon across the
entire CWA. A much drier airmass will settle in by midweek as
moist southwesterly flow transitions to a dry westerly flow. ~37%
of ensemble members keep conditions mostly dry through Friday, but
the remaining 63% of members begin to advect more moisture into
the CWA that could lead to more diurnal convection.

Instability will be enhanced across northern Utah/SW Wyoming on
Sunday as mean ensemble CAPE values ~500 J/kg and shear ~35kts
will increase the risk for strong to severe storms. Storm motions
across the north will be relatively fast which will help to limit
the flash flood threat, but slower storm motions and PWATs near
the 90th percentile across southern Utah will increase the flash
flood threat. Slightly less instability and moisture Monday and
Tuesday across northern Utah along with faster storm motions
across southern Utah indicates that Sunday will likely be the day
with the greatest risk for strong convection across the north and
flash flooding across the south.

By Wednesday a much drier airmass along with gusty southwesterly
winds across portions of the CWA could increase the fire weather
risk. Currently, RH looks to remain >15% for most locations which
would help to lessen the fire weather risk. This window of dry and
windy weather appears to be short-lived as 63% of ensemble
members bring a return to a moist southerly flow by Friday.

&&

.AVIATION....AVIATION...KSLC...Light southeast winds will prevail
through the evening, but showers and thunderstorms with gusty, erratic
outflow winds could alter direction and enhance speeds from
00-03Z. Southeast winds, with gusts around 20 knots, are likely
overnight. There is around a 30% chance for showers and
thunderstorms capable of gusty, erratic outflow winds from roughly
20-03Z.

.REST OF UTAH AND SOUTHWEST WYOMING...Showers and thunderstorms
capable of localized heavy rain and gusty, erratic outflow winds
throughout southwest Wyoming and northern Utah will diminish around
03Z. Showers and thunderstorms with the same threats throughout
southern Utah will continue through around 06Z. There will be
largely dry conditions overnight. Scattered showers and
thunderstorms are likely for southwest Wyoming and much of Utah from
roughly 20-03Z.

&&

.FIRE WEATHER...Deep moisture associated with a modest monsoonal
push is spreading further north today, and trends moving forward
through the weekend will continue that same path. For central and
southern Utah potential for scattered heavy rain events will
remain elevated, while storms developing in the north will favor
more wind than rain, with microburst wind potential remaining
elevated each for the next few days. A combination of net
weakening of the the high pressure driving this moisture surge,
and the grazing of a weak disturbance early next week will
begin to dry things out from the west by midweek of next week.
Looks dry and breezy across the western zones (at least) for
the midweek period coming up.

&&

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

Merrill/Wilson/Mahan

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

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