Special Weather Statement, NWS Salt Lake City, UT

Area Forecast Discussion
National Weather Service Salt Lake City UT
331 PM MDT Fri Aug 5 2022

.SYNOPSIS...Increased moisture will remain in place over the area,
especially northern Utah, through Saturday. A brief drying trend is
expected late in the weekend into early next week, with some
potential for another moisture surge for the second half of next
week.

&&

.SHORT TERM (Through 12Z Sunday)...Utah and southwest Wyoming are
under southwest flow this afternoon ahead of a trough currently
centered over Nevada. This has moved deep moisture into northern
Utah with a drying trend observed over southern Utah.
Additionally, the position of the trough has put northern Utah
under a more unstable than usual environment with 30+ knots of
shear across a broad area. In this environment, have already seen
some strong to severe convection develop with the potential
continuing through the early evening. Organized convection could
produce strong gusty winds and small hail in addition to heavy
rain that could cause flooding issues, particularly for active
burn scars.

The trough will eventually slide across northern Utah tomorrow
morning into the afternoon. Though it will be weakening, it will
be accompanied by a frontal boundary that will act as a focus for
widespread convection, though this precipitation may be steadier
in nature, limiting the potential for strong/severe convection.
The front and cloud cover will also keep temperatures down, with
maxes running 5-10F below seasonal normals.

.LONG TERM (After 12Z Sunday)...The long term period will
start off with a shortwave moving out of the area leaving drier
conditions for much of the forecast area for Sunday and into Monday.
The greatest chance for precipitation will primarily be in the
Eastern Valleys as that shortwave moves eastward, while isolated
PoPs are expected for southern Utah. PWAT values are expected to
decrease Sunday before slowly increasing to around an inch for
southern Utah during the day on Monday.

By Monday, as the shortwave continues pushing east and a low
pressure system moves eastward toward the PacNW, this allows for
ridging to build back in. With this ridge building back in, an
increase in moisture flow will return to southern Utah. The chances
for precipitation still remain on the low side for Monday as the
moisture flow is going to come back slowly. Dry conditions are
expected for the rest of the forecast area.

As Tuesday rolls around, the ridge will continue to build and
strengthen. There is some uncertainty in both the deterministic
models and ensemble runs as to where the position of the ridge
axis will be. If the ridge axis stays over the forecast area or
near it, the amount of monsoonal moisture flow will not be as much
and northern and central Utah will be drier. A majority of GEFS
and ECMWF ensembles favor this solution. Whereas the CMC ensembles
and deterministic favors the ridge axis already shifting further
east. This allows for more monsoonal moisture flow and an increase
in precipitation chances. Something that does not have
uncertainty is PWAT values. These values will continue to increase
as the ridge strengthens and moves east.

After Tuesday, guidance is in much better agreement on the position
of the ridge axis. The ridge axis is expected to move further east
allowing for a greater moisture flux and a continued increase in
PWAT values. In addition to the increase in moisture, there will
also be a shortwave moving into the area Wednesday into Thursday and
sticking around for the forecast period. This shortwave will help
bring an increase in the possibility of precipitation for central and
northern Utah. Precipitation chances as a whole look to be
increasing across the CWA. This pattern looks to persist for the
rest of the forecast period. With the combination of high PWAT
values, a good moisture flux, and decent instability, convection
with decent rainfall rates are possible. Flash flooding, especially
for burn scars and slot canyons, will also be possible given the
conditions.

&&

.AVIATION...KSLC...Winds are expected to prevail from the northwest
through 03Z. A transition to southeast flow is expected around 03Z.
Scattered showers and thunderstorms through the evening will result
in outflow that could cause erratic winds. Scattered showers or an
isolated thunderstorm are possible through 09Z. Dry conditions are
expected from 09Z through the rest of the morning, with better
shower and thunderstorm chances during the afternoon.

.REST OF UTAH AND SOUTHWEST WYOMING...Scattered showers or an
isolated thunderstorm are expected for southwest Wyoming and
northern Utah through 09Z. Light rain is expected through much of
the night for northwest Utah. Showers and thunderstorms will slide
eastward through Saturday, with precipitation possible much of the
afternoon for southwest Wyoming and northern Utah. Conditions are
expected to be dry throughout southern Utah, with gusty southwest
winds diminishing around 03Z.

&&

.FIRE WEATHER...Deep moisture remains over northern Utah this
afternoon with somewhat drier conditions over southern Utah. Ahead
of an approaching weather disturbance, showers and thunderstorms
will become widespread over northern Utah this afternoon into this
evening with the potential to produce gusty and erratic winds
along with heavy rain. The disturbance will move through beginning
Saturday morning, bringing the potential for more widespread
wetting rains. High pressure will move in behind the exiting
disturbance for Sunday and Monday, resulting in a drying trend and
a relative lull in showers and thunderstorms. Moisture may return
again by midweek.

&&

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

SHORT TERM/FIRE WEATHER...Traphagan
LONG TERM...Cecava
AVIATION...Wilson

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