182
FXUS66 KSGX 212116
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
216 PM PDT Fri Jun 21 2024

.SYNOPSIS...
Hot conditions expected through the weekend for the valleys,
mountains, and deserts and in the deserts next week. A surge of mid-
level moisture will bring higher humidity and a slight chance for
showers and thunderstorms from the coast to the deserts late
Saturday night into Sunday, locally in the San Bernardino mountains
on Monday afternoon. A shallow marine layer will keep coastal highs
in the 70s and 80s.

&&

.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...

A ridge of high pressure currently over Texas, will drift west
towards the Southwest United States this weekend. That ridge of high
pressure will remain over the Four Corners region through most of
next week. The ridge will result in hot conditions across Southern
California and allow for an increase in mid-level moisture Sunday,
with some moisture lingering into Monday. Widespread moderate to
major heat risk away from the coast is expected on Saturday.
Temperatures will get knocked down a few degrees on Sunday for
inland areas due to an increase in moisture. Even with temperature
readings a few degrees lower than Saturday, hot and muggy conditions
are expected with highs 5 to 10 degrees above average.

Temperatures for locations in and west of the mountains will peak on
Saturday, gradually decreasing into next week. Widespread moderate
heat risk will continue into Sunday in and west of the mountains,
with heat risk becoming locally moderate for the eastern portions of
the valleys by Monday. High temperatures in the deserts will fall a
few degrees on Sunday, before increasing again for Monday.
Conditions in the deserts will remain hot enough for moderate to
major heat risk through Thursday. For the end of next week, a trough
of low pressure will approach the Pacific Northwest, weakening the
ridge and pushing it off to the south and east. This will allow
temperatures to fall to within a few degrees of the seasonal normals.

For Sunday, a surge of mid-level moisture will bring higher humidity
to the area. The increased humidity will make it harder to keep cool
during outdoor activities even with high temperatures a few degrees
cooler than Saturday. Model guidance continues to show an easterly
wave in the southeast flow around the Four Corners making it`s way
across Southern California Sunday. This shortwave interacting with
the mid-level moisture will destabilize the atmosphere sufficiently
for showers and thunderstorms Saturday night and Sunday from the
coast to the deserts. The increase in Most Unstable CAPE in the mid-
levels of the atmosphere over the coastal waters and near the coast
is indicating the potential for elevated convection which could
bring thunder and lightning with little to no rainfall accumulation.
Measurable precipitation (25-35%) and thunderstorms (15-20%) are
most likely over the mountains, with lesser chances of measurable
precipitation (15-20%)and thunderstorms (5-10%) for the coast,
valleys, and deserts. Isolated thunderstorm chances will linger
Monday afternoon in the San Bernardino Mountains (20%).

&&

.AVIATION...
212042Z...Coast/Valleys...Some SCT-BKN low clouds over the coastal
waters otherwise mostly clear.

After 22/03Z this afternoon low cloudS with bases 1100-1300 ft MSL
with tops to 1700 ft MSL moving in with local VIS 3-5 miles in BR
over higher coastal terrain and western portions of the valleys.
Cloud coverage becoming more erratic Sat morning. CIG and/or VIS
impacts not expected at KONT or KSBD. Confidence in return time of
the low clouds at KSAN of around 05Z is moderate.

Mountains/Deserts...Mostly clear with unrestricted VIS through Fri
evening. West winds with gusts 20-35 kt through San Gorgonio Pass
and other favored locations on the desert slopes and into the
deserts will continue to weaken through late Friday.

&&

.MARINE...
A system moving by to the south will bring a small chance (less than
20%) of precipitation and a 10% or less chance of lightning Saturday
night through Sunday. Otherwise, no hazardous marine conditions are
expected through next Wednesday. See the Marine Weather Statement
for more information on the potential for thunderstorms.

&&

.BEACHES...
There is a slight chance of a thunderstorm Saturday night through
Sunday which could produce cloud-to-ground/cloud-to-water lightning
strikes. Chances of a lightning strike near any particular beach are
currently 10 percent or less Saturday night and Sunday.

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Heat Advisory from 10 AM Saturday to 8 PM PDT Sunday for Orange
     County Inland Areas-San Bernardino and Riverside County
     Valleys-The Inland Empire-San Diego County Valleys.

     Heat Advisory from 10 AM to 8 PM PDT Saturday for Riverside
     County Mountains-San Bernardino County Mountains-San Diego
     County Mountains.

     Excessive Heat Warning from 10 AM Saturday to 8 PM PDT Thursday
     for Apple and Lucerne Valleys-Coachella Valley-San Diego
     County Deserts-San Gorgonio Pass Near Banning.

PZ...None.

&&

$$

PUBLIC...CO
AVIATION/MARINE/BEACHES...Small