Tustin Foothills, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

161
FXUS66 KSGX 140950
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
250 AM PDT Mon Apr 14 2025

.SYNOPSIS...
Little change in temperatures today followed by more significant
cooling Tuesday through Friday. By Friday, high temperatures will
be 10-20 degrees below normal. The marine layer will deepen
through the week, filling in across the coastal basin by
Wednesday. Patchy drizzle is possible west of the mountains each
morning Tuesday through Thursday, followed by a 15-40 percent
chance of precipitation Thursday night through early Saturday.
Warmer and drier early next week.

&&

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

The 00Z KNKX sounding shows the marine inversion based near 1800
ft MSL, down from around 2200 ft yesterday morning. Marine layer
low clouds have filled in over the coastal areas and western
valleys, and will continue progress into the western and southern
portions of the Inland Empire through the morning. Otherwise there
were scattered high clouds moving north over the region ahead of
an upper level low around 275 mi to our southwest. This low will
open up and become a negatively tilted trough as it moves into So
Cal and Arizona tonight. Overall not much change in temperatures
today with highs near to slightly below normal west of the
mountains but still 5-10 degrees above normal in the mountains
and deserts.

The passing wave tonight will cause the marine layer to deepen,
potentially producing some patchy drizzle Tuesday morning. The
path of the trough axis and associated vort max has trended
further east, bringing less moisture and dynamics to So Cal, so
precipitation chances over the mountains have dropped below 15%
for tonight. Otherwise cooler Tuesday with breezy onshore winds
below the passes Tuesday evening as another closed low develops
off the coast. This low will progress westwards into Wednesday,
opening up and moving into CA on Thursday as it phases with
another trough dropping south through the Pac NW. This will
maintain the cooling trend and generate stronger southwest to west
winds across the desert mountain slopes and below the passes each
afternoon and evening. The marine layer deepens significantly,
bringing more late night and morning drizzle to areas west of the
mountains. Some high-res guidance even shows legitimate showers
from the marine layer on Thursday morning as it deepens to around
5000 ft.

There is still some uncertainty with the evolution of the upper
pattern late in the week. About 40% of the ensemble members
maintain a large low progressing south into CA/NV, another 23%
keep more of an inside track through NV/UT, and another 37% with a
less amplified wave and an inland track. The track of this low has
big implications on virtually every aspect of the forecast:
temperatures, snow levels, precipitation amounts, thunderstorm
chances, and wind. By Saturday around 45% of the members have the
closed low somewhere over interior So Cal/southern NV, while
another 36% maintain the inside slider track. If the low moves
closer to us, expect cooler weather, higher precipitation amounts,
and stronger onshore flow. The inside track will produce less
cooling, lower precipitation amounts, and weaker winds. Depending
on how far inside it tracks, we could end up with no precipitation
outside of whatever drizzle/light showers the marine layer manages
to produce. For now, the forecast maintains a 15-40% chance of
precipitation Thursday night and Friday for all areas expect the
lower deserts, with showers tapering off from north to south
Friday evening into Saturday morning.


&&

.AVIATION...
140930Z...Coasts/Valleys...Low clouds based 1000-1500 ft MSL and
tops up to 2000 feet MSL will continue to spread into the Inland
Empire. VIS reductions limited to the coastal slopes of the
mountains and foothills. Low clouds scatter out in the inland
valleys first after 15-16z, with the coasts clearing out by 18-19z.
Slightly higher based low clouds will redevelop this evening and
push inland after 03z. The coastal basin should fill in completely
before 12z Tuesday morning.

Elsewhere...SCT-BKN high clouds above 20000 feet MSL. Local west
wind gusts 25-35 kt over the mountains into the passes and deserts
return after 22z today and last through the evening.

&&

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

&&

.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...SS
AVIATION/MARINE...KW