351
FXUS66 KSGX 210932
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
232 AM PDT Fri Aug 21 2026

.SYNOPSIS...
Monsoonal moisture will decrease into the weekend with a slight
chance of showers and thunderstorms for the mountains and high
desert for this afternoon. Above average high and low temperatures
will continue through next week. Slightly warmer high and low
temperatures for the middle and latter part of next week will
increase the HeatRisk with widespread moderate to locally major
HeatRisk for the coast, valleys, and mountains except near the
beaches and for the higher elevations in the mountains, with
major to extreme HeatRisk for the lower deserts.

&&

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


...UPDATED AVIATION DISCUSSION...

.SHORT TERM (Today through Sunday)...
A Mesoscale Convective Vortex that was initiated by thunderstorms
over Arizona last night is now tracking toward the northwest and
north in the southerly flow between the low pressure system off
the West Coast and high pressure over the Rockies. Showers have
developed over portions of western Riverside County and will
spread northward into San Bernardino County for the remainder of
the night. There is also a slight chance of thunderstorms.

Precipitable water values were forecast to peak over southwestern
California on Thursday, then decrease into the weekend. Scattered
showers and thunderstorms may develop this afternoon along
convergence boundaries along the desert slopes of the mountains
and northward across the Lucerne Valley in the high desert. Dry
weather is then expected through the weekend.

High temperatures for the lower deserts will warm a few degrees
today as drying of lower level moisture occurs. Otherwise, there
will be slight day to day differences in high temperatures
through the weekend. High temperatures for the weekend will be a
few degrees above average near the coast to 4 to 8 degrees above
average for inland areas. High temperatures for the weekend will
range from the mid 70s to lower 80s near the coast to the upper
90s to 104 for the Inland Empire with 110 to 114 for the lower
deserts.

&&

.LONG TERM (Monday through Thursday)...
There may a brief increase in lower level moisture into the lower
deserts around Monday with high temperatures for the lower deserts
not quite as hot by a few degrees on Monday. Otherwise, high
pressure to the east and low pressure over the eastern Pacific
will maintain generally drier south to southwest flow aloft next
week. High temperatures for next week will be around 5 degrees
above average near the coast to 5 to 10 degrees above average for
inland areas. High temperatures will range from around 80 near the
coast to the upper 90s to 108 for the Inland Empire with 110 to
115 for the lower deserts and the upper 90s to 108 for the high
desert.

Low temperatures will be around 5 degrees above average near the
coast to 5 to 10 degrees above average for inland areas with the
lower elevations of the mountains locally 10 to 15 degrees above
average. For Wednesday through Friday, low temperatures will be
mostly in the lower to mid 70s for the coast and valleys.

Major HeatRisk will continue for the lower deserts through next
week with major to extreme HeatRisk for Thursday and Friday of
next week. By Tuesday of next week, widespread moderate to locally
major HeatRisk is expected for the coast, valleys, mountains, and
high desert except near the beaches and for mountain elevations
above 6500 feet, mostly due to the warmer nights. The Extreme Heat
Warning for the lower deserts has been extended through Friday of
next week, August 28th.

&&

.AVIATION...
210930Z...Coast...Patchy low clouds based 800-1200 ft MSL over the
coastal waters will remain patchy and intermittent at best for
coastal areas through early this morning.
Low clouds expand in coverage near sunrise with the best
chance for cigs at coastal TAF sites 12-15z. VFR conditions expected
this afternoon. Similar conditions expected tonight, with
patchy low clouds generally remaining over the coastal waters with
best chances for cigs at coastal sites Sat morning after 11z.

Otherwise...FEW to SCT clouds above 15 kft MSL through
Friday. Slight chance (10-15%) for ISO SHRA/TSRA over mtns from
20z Fri to 01z Sat.

&&

.MARINE...
No hazardous marine conditions are expected through Tuesday.

&&

.SKYWARN...
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.


&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Extreme Heat Warning until 8 PM PDT Friday for Coachella Valley-
     San Diego County Deserts-San Gorgonio Pass near Banning.

PZ...None.

&&

$$

PUBLIC...17
AVIATION/MARINE...CSP