950
FXUS66 KSGX 120403
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
903 PM PDT Thu Jul 11 2024

.SYNOPSIS...
A gradual slow cooling trend for Friday through Sunday and then
steady next week. Night and morning coastal low clouds will
continue to spread into portions of the western valleys late each
night. Deeper monsoonal moisture will begin to arrive on Friday
and peak over the weekend with a chance of mainly afternoon and
early thunderstorms for the mountains and deserts for Saturday and
Sunday. Drying will develop on Monday and persist next week.

&&

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

Marine clouds were slow to clear again especially northern San
Diego county coastal. Todays highs were just a tad below Wednesday
for Inland Empire areas but they were actually warmer on the
coastal and San Diego valleys with mid to upper 90s. We saw the
ending of the heat wave spike in the High Desert with 108F at
Hesperia and up about 1F for the lower desert. Fog and low clouds
will be similar to last night but a very slight rise in marine
layer depth. The 596 DM 500 mb upper high lower to 594 DM by
Friday as we start the slow cooling mostly due to moistening
in the mid levels under monsoonal flow from the south. The
hot air mass of 30-33C at 850 mb drops 1C each day and up
to 2c on Saturday with a mid level wave arriving on the backside
of the upper high. By Sunday, the air mass is 25-28C. Despite
cooling aloft the marine layer may not respond much due to
increased in mid level moisture. Beach water temperatures
are now in the lower 70s expect upper 60s in northern Orange
County.

Will need to watch the mid level wave possible for Saturday in
addition to the high precipitable water surge from Friday
to Saturday. While primary convection would be surface based
over the mountains the steering flow could take cells off the
high terrain to the west, and there is elevated non-surface
based convection potential on Saturday due to the mid level
wave lifting the elevated instability in place.

Air mass dries again and warms very slightly early next week
so this ends the convection thunderstorm threat and reduces
cloud cover.


&&

.AVIATION...
120400Z...Coast/Valleys...Low clouds moving inland with bases near
700-1000 feet MSL and tops 1200-1500 feet MSL for coastal sites,
bases falling to 300-700 feet MSL around 12/06z-12/09z. Visibility at
or below 3SM for coastal sites overnight and through the morning,
brief localized visibility below 1SM possible in valleys and spots
along the coast around 12/10z-12/16z. CIGs at coastal sites will
scatter out between 12/16z-12/18z, with clouds hanging offshore
through the afternoon. Marine layer moves inland late Friday, with
bases at coastal sites slightly higher than today.


Mountains/Deserts...Mainly VFR with afternoon FEW-SCT200 for areas
along and east of the mountains. Localized VIS reductions down to
3SM due to smoke in the vicinity of the San Bernardino Mountains
from the Vista fire. Winds generally light, but periods of gusty
northwesterly winds possible up to 30kts around San Gorgonio Pass
through Friday evening.

&&

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

&&

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


&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Excessive Heat Warning until 9 PM PDT Friday for Apple and
Lucerne Valleys-Coachella Valley-San Diego County Deserts- San
Gorgonio Pass Near Banning.

PZ...None.

&&

$$

PUBLIC...Tardy
AVIATION/MARINE...Zuber/MKM