Subj : DAY1SVR: Day 1 Convective Outlook
To   : wx-storm@lists.illinois.edu
From : COD Weather Processor
Date : Sun Aug 20 2023 06:00:00

ACUS01 KWNS 200559
SWODY1
SPC AC 200558

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1258 AM CDT Sun Aug 20 2023

Valid 201200Z - 211200Z

....THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
SOUTHERN CALIFORNIA...

....SUMMARY...
Tropical cyclone Hilary will move across southern California today.
A tornado threat is expected to develop in parts of southern
California this afternoon. Isolated damaging winds will be possible
across much of the Mojave Desert and Arizona this afternoon and
evening.

....Southern California/Desert Southwest...
Hilary is forecast to make landfall along the coast of Mexico to the
south-southeast of San Diego this morning. Hilary is forecast to
move northward into southern California during the afternoon.
High-resolution model forecasts suggest that discrete storms will
develop on the eastern side of the system by late morning. These
storms are forecast to move northward into southern California
during the early afternoon. RAP forecast soundings by 21Z ahead of
these storms, and to the east of Los Angeles suggest that surface
temperatures will peak in the 80s F by mid afternoon. In addition,
model forecasts move a strong low-level jet into southeastern
California during the afternoon. Within the nose of this jet,
low-level shear and lift will be maximized. RAP forecast hodographs
show strong speed shear, and a gradual veering of winds with height
in the low to mid-levels. 0-3 km storm-relative helicity is forecast
to reach the 300 to 400 m2/s2 range. This will be favorable for
rotating storms with tornado potential. The area with the greatest
tornado threat is forecast to develop across southwestern parts of
the Mojave Desert between San Diego and the Colorado River, as the
nose of the low-level jet moves through. A thunderstorm wind-damage
threat is also expected to develop to the east of the forecast track
of Hilary, from parts of southern California, northward into
southern Nevada and far southwest Utah, and eastward across much of
Arizona.

...Broyles/Weinman.. 08/20/2023

$$

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