713
FXUS66 KSGX 242003
AFDSGX
Area Forecast Discussion
National Weather Service San Diego CA
103 PM PDT Wed Jun 24 2026
.SYNOPSIS...
A slight chance of showers and thunderstorms will continue into
this morning, mainly for the mountains and deserts of San
Bernardino County. A low pressure system to the north will bring
stronger onshore flow and a cooling trend for Thursday through
the weekend with Sunday high temperatures near the coolest for the
date for a few locations. Southwest to west winds for the
mountains and deserts during the afternoon and evening will
strengthen for Thursday through Saturday, then weaken for early
next week. The marine layer will deepen late in the week into the
weekend with night and morning coastal low clouds extending well
inland and onto the coastal slopes of the mountains for early
Saturday. Then warmer for early next week, but with high
temperatures remaining below average.
&&
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
Current satellite this afternoon shows a notable decrease in mid
level cloud coverage from southwest to northeast as the shortwave
trough that provided a bolster of moisture and synoptic lift has
progressed into the Great Basin. With this, we expect an end to the
elevated shower chances for the San Bernardino Mountains and High
Desert by mid-late this afternoon. Meanwhile, strong upper level
high pressure in control across the desert southwest has a ridge
axis stretching westward over southern California. This and the
added moisture from the monsoonal disturbance aloft is yielding mild
afternoon high and overnight low temperatures, with some minor
HeatRisk for the inland valleys, with moderate HeatRisk in the
deserts. Portions of the lower Deserts of San Diego Valley are
seeing locally major HeatRisk with the highest combination of
temperature and humidity, where an Extreme Heat Warning remains in
effect through 8 PM Thursday. Thursday will mark the beginning of a
late week cooling tend, but with another mild night before the mid
level moisture and increase humidity fully depart, so there is still
moderate HeatRisk in the deserts into the afternoon.
All attention quickly turns to a highly unseasonable trough that is
set to push into the Pacific Northwest on Thursday/Friday. This
trough will kick out the monsoonal moisture for good, shove the
ridge south and east, and bring much cooler air to the region for
the weekend and into next week. Ensembles and clusters provide good
confidence in the strength and progression of this large and
anomalous trough, set to dive down into California and dominate
across the West for the weekend. Temperatures quickly fall below
normal area wide by Friday, with afternoon high temperatures likely
to fall 15 to even 20 degrees below normal for Saturday and Sunday.
The currently forecast temperatures are so unseasonably low that
record cool high temperature forecasts could be challenged this
weekend. In addition to the cool temperatures, this trough will
bring a strengthening trend for the onshore winds, especially for
the desert mountain slopes and deserts. Wind gusts on Friday
afternoon could be near Advisory-level criteria with 35-40 mph for
the deserts, and locally 45-60+ mph in mountain passes. The
strongest winds look to peak Saturday afternoon, and then weakening
into Sunday. Dry conditions in the High Deserts will likely bring
elevated fire concerns, so see the Fire Weather Section below for
more details.
Looking ahead into next week, ensembles indicate the large could
could get a few reinforcing shortwaves that could extend its
presence across the western US well into middle part of next week.
NBM currently favors below normal temperatures lingering across
SoCal through at least Wednesday.
&&
.AVIATION...
241730Z...Coast/Valleys...Mostly clear today, except for patches of
low clouds with bases 1200-1500 feet MSL persisting at the beaches.
Cigs at the same level will push ashore after 03Z and inland
overnight, slightly farther into valleys by 11-15Z Thursday. Vis
reduced 1-5SM in valleys. Scatter out Thursday 17-19Z.
Mountains/Deserts...SCT-BKN clouds 10000-20000 feet MSL will
continue today, but decrease and move east after 23Z, leaving mostly
clear skies into Thursday morning.
&&
.MARINE...
No hazardous marine conditions are expected through Monday.
&&
.BEACHES...
A long-period south swell will continue to bring surf of 3 to 6 feet
through Thursday, highest on south facing beaches. See the Beach
Hazards Statement for details.
&&
.FIRE WEATHER...
The swath of mid level moisture and associated upper level
disturbance that provided the risk for dry thunderstorms yesterday
and this morning has now departed to the northeast into the Great
Basin this afternoon. This has decreased the chances for elevated
showers/storms and the remaining risk for dry lightning has gone
away.
Looking ahead to this weekend, a very unseasonably strong upper
trough is set to dig across the Pacific coast late this week,
brining a 50-60kt 500 mb jet overhead by late Friday. This will
strengthen our onshore flow Thursday into Friday, with the strongest
gusts found across the desert mountain slopes and deserts. These
gusts (generally from the west-southwest at 35-45 mph) could
likely combine with afternoon humidity of 10-15 percent across
the High Desert to created elevated to locally critical fire
weather conditions Friday afternoon. While the winds strengthen
further and peak Saturday afternoon, the exposure of the elevated
onshore flow will help pull moisture into the high desert,
bringing afternoon humidity closer to 20-30 percent along with
the cooler temperatures. Winds begin to weaken into Sunday, but
the increased moisture should linger, limiting widespread concerns
this weekend to largely Friday afternoon.
&&
.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Beach Hazards Statement through Thursday evening for Orange
County Coastal Areas-San Diego County Coastal Areas.
Extreme Heat Warning until 8 PM PDT Thursday for San Diego
County Deserts.
PZ...None.
&&
$$
PUBLIC/FIRE WEATHER...Munyan
AVIATION/MARINE...MM
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