Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
346 AM EDT Sat Aug 19 2023

Valid 12Z Sat Aug 19 2023 - 12Z Mon Aug 21 2023

...Catastrophic and life-threatening flooding likely over portions of the
Southwest...

...Dangerous heat expanding over the central U.S.....

Hurricane Hilary has now turned north-northwestward and is forecast to
track near Baja California before making landfall near the U.S.-Mexico
border later this weekend.  Heavy rainfall associated with the system is
forecast to develop across the southwestern U.S. today, well in advance of
the storm's center, and continue through the weekend, with the heaviest
amounts expected on Sunday.  Highly anomalous moisture transport into the
region will support rainfall amounts exceeding the average annual totals
for some locations in the Southwest.  Flash, urban, and arroyo flooding is
expected, with dangerous and locally catastrophic impacts likely.  In
addition to flooding rains, Hilary is forecast to bring tropical storm
conditions to portions of southern California on Sunday.  Large swells
will affect portions of southern California over the next few days.  These
swells are likely to cause life-threatening surf and rip current
conditions.  Widespread cloud cover will keep temperatures below average,
with unseasonably cool temperatures forecast to expand northward from
southern California and western Arizona into the Sierra Nevada and the
Great Basin through the weekend.

In contrast to the temperatures in the West, dangerous heat will continue
to intensify and expand, with well above-normal to record-breaking
temperatures forecast across the Plains and lower Mississippi Valley
today.  The heat wave will continue to expand on Sunday to include more of
the Midwest on Sunday.  This weekend, some locations in the Midwest may
experience their hottest day of the year.  The prolonged nature of the
heat wave, combined with very warm overnight temperatures, will limit
relief from the oppressive daytime temperatures and compound the overall
heat impacts.

A relatively quiet period is expected for much of the eastern U.S., with
shower and thunderstorms confined mainly to Florida and the Southeast
coast.  After another day of seasonal to below-average temperatures today,
summer heat is forecast to return to much of the Northeast and
Mid-Atlantic states on Sunday.
   
Pereira

Graphics available at
https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php