Base Line, California Weather Forecast Discussion

790
FXUS66 KSGX 261652
AFDSGX
Area Forecast Discussion
National Weather Service San Diego CA
952 AM PDT Fri Sep 26 2025
.SYNOPSIS...
There is a slight chance of showers and thunderstorms this
afternoon for the mountains and deserts. Chances for showers and
thunderstorms increase on Saturday for the mountains and deserts
and expand to the inland valleys during the afternoon. Dry
conditions return by Monday. A brief warming trend is expected through
the weekend with cooling Tuesday. Increased southwest to west
winds for the mountains and deserts and cloud coverage can also be
expected for Tuesday. A gradual warming expected Wednesday
through the rest of the week.
&&
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
Visible satellite this morning was showing widespread cloud coverage
in the coastal basin with areas of high clouds in the deserts. A
closed low pressure system will move into southern California today,
linger along the southern California border with northern Baja on
Saturday, the weaken and move to the east on Sunday. As the center
of upper level low pressure moves into the eastern deserts of
southern California this afternoon, our chances for showers and
thunderstorms begin to increase as moisture and instability
spreads into the area from the north. The center of low will move
to the border of southern California and northern Baja on Saturday
with moisture spreading into the area from the east. This will
bring an increased chance of showers and thunderstorms for the
mountains, deserts, and valleys. The greatest chances are for the
mountains and deserts of 35 to 45 percent during the afternoon.
High resolution guidance is indicating rainfall rates will be
mostly 0.50 to 1 inch per hour with the potential for isolated
rates to exceed one inch an hour, most likely in the mountains.
Areas of flash flooding possible for the mountains, especially
near burn scars. More isolated flash flooding is possible in the
deserts and inland valleys.
The low pressure system will weaken and move east on Sunday with a
10 to 20 percent chance of showers and thunderstorms for the
mountains and deserts on Sunday afternoon from lingering moisture
and instability. Rainfall rates on Sunday are expected to be lower
than Saturday, with high resolution guidance showing rainfall rates
below 0.50 inches an hour. Dry conditions are expected by Monday.
Cooling will continue today with high temperatures for inland
areas 5 to 10 degrees below average and locally 10 to 15 degrees
below average for the inland valleys onto the lower coastal
mountain slopes. The lower deserts will cool a few more degrees on
Saturday with the coast and valleys warming slightly. Most areas
will be a degree or two warmer on Sunday, with continued warming
into Monday. An incoming trough of low pressure will begin to
influence our weather on Tuesday, bringing cooler conditions with
increased cloud coverage and west to southwest winds in the
mountains and deserts. High temperatures on Tuesday will mostly be
5 to 10 degrees below average for inland areas to locally 10 to
15 degrees below average for the higher elevations of the
mountains. This will be followed by slow warming through the rest
of the week with high temperatures on Thursday still a few degrees
below average for inland areas.
&&
.AVIATION...
261630Z....Coasts/Valleys/Foothills...Clouds based at 3000-4000 feet
MSL with tops to 4500 ft MSL are covering the coastal basin. is
reduced in foothills. Only partial, random, and intermittent scatter
out is expected for anywhere in the coastal basin today, with bases
around 2500-3500 feet MSL. BKN-OVC conditions will develop across
the coastal basin into foothills again tonight after 05Z into
Saturday morning.
Mountains/Deserts... 20% chance of TSRA 19-01Z across mountains and
high desert. Bases around 10000 feet MSL and storm tops to 30K feet.
An isolated SHRA/TSRA is also possible (20-30% chance) overnight
into early Saturday, mainly along desert slopes but also in the
vicinity of lower desert communities.
&&
.MARINE...
No hazardous marine conditions are expected through Tuesday.
&&
.BEACHES...
South swell from Hurricane Narda will arrive this weekend. Swell of
4-5 feet with a period of 12-14 seconds will produce elevated surf
and a high rip current risk Sunday through Tuesday, especially for
south facing beaches, where sets could reach 7 feet.
&&
.SKYWARN...
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.
&&
.SGX WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...None.
&&
$$
PUBLIC...CO
AVIATION/MARINE/BEACHES...Westerink

NWS SGX Office Area Forecast Discussion