High Wind Watch 8, NWS Salt Lake City, UT

Area Forecast Discussion
National Weather Service Salt Lake City UT
310 PM MDT Fri Aug 18 2023

.SYNOPSIS...Deep moisture will remain in place through the
weekend. Moisture from Hurricane Hilary will impact the area
later this weekend into early next week.

&&

.DISCUSSION...Another very busy afternoon across the CWA, with
another relatively brief discussion. Afternoon upper air and
satellite analysis indicates a rather unusual feature. Category 4
Hurricane Hilary is offshore the southern tip of Baja California.
Tropical Storm Watches have been hoisted for southern California
for the first time. Meanwhile an upper level low remains off the
coast of California, with broad ridging roughly centered across
the Red River remains in place.

Over the next few days, Hurricane Hilary will shift north and
accelerate while moving into less favorable waters. This will
result in the potential for a weakening Tropical Storm Hilary to
make landfall across southern California later Sunday.

The main message for Utahns, however, is deep tropical moisture
will move into the area well ahead of landfall. The main threat
with now Hurricane Hilary for Utah will be very heavy rain, as
the current track would not support any wind threat. Current
ensembles support the heaviest rain along the Utah/Nevada border
east to the crest of the mountains through Monday; potentially
into Tuesday.

There will not be any real break between our current monsoon
surge and the increase in tropical moisture...with a shift toward
the increasing tropical moisture across at least the western half
of Utah later Saturday.

For now, expanded the flood watch for central and southern Utah
through 06Z Sunday and added in two additional zones with recent
burn scars (the western Uinta Mountains and the Book Cliffs and
Wasatch Plateau) for Saturday. With additional recon flights
increasing the availability of high quality data ingest into the
00Z and later models, will monitor whether additional watch
extensions will be needed for Sunday or Monday.

Takeaway message: the flash flooding threat will remain elevated
through early next week across a sizable portion of the region.
Those who are near dry washes, recent burn scars, in areas with
poor drainage and/or typically see flooding issues with heavy rain
should prepare now for any impacts (especially across the western
half of Utah). This is not the weekend to hike slot canyons,
normally dry washes or other areas with high flood exposure. And
finally, taking a few extra minutes to deviate around a flooded
road. It is worth saving your life. Do not drive through flooded
areas; turn around, don't drown.

&&

.AVIATION...KSLC...Isolated showers are possible this afternoon.
Light northwest winds expected until ~01Z when gusty southerly
winds, up to 25kts, are expected as an outflow boundary moves
northward through the valley. Winds through the afternoon could be
variable at times as wind speeds will be light. There is a 40%
chance that southerly winds will remain through Friday afternoon
and evening. Southerly winds will persist through the night until
switching back northerly between 20Z and 22Z Saturday. VFR
conditions expected.

REST OF UTAH AND SOUTHWEST WYOMING...Scattered showers and
thunderstorms will be possible for much of Utah until ~04Z.
Isolated showers and thunderstorms for northern Utah and southwest
Wyoming until 04Z as well. Predominant southwest flow for most
areas until ~06Z when diurnal winds kick in. Gusty and erratic
outflow winds winds will be possible with these storms. VFR
conditions expected across Utah and southwest Wyoming for the TAF
period.

&&

.FIRE WEATHER...An ongoing monsoon surge will transition into an
increase in tropical moisture associated with now Hurricane
Hilary over the next few days. This will bring the threat of heavy
rain and widespread wetting rains, especially near and west of
I-15. As Hurricane Hilary weakens into an extratropical system
late this weekend into early next week, deep moisture will remain
in place. With little change in the airmass, daily shower and
thunderstorm chances will continue into the end of the week.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Flood Watch from Saturday morning through Saturday evening for
     UTZ112-113.

     Flood Watch through Saturday evening for UTZ117-119-122>131.

WY...None.
&&

Kruse/Cecava

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