Lake San Marcos, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

406
FXUS66 KSGX 092123
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
223 PM PDT Fri May 9 2025

.SYNOPSIS...
The hottest day of the year so far is expected on Saturday with
high temperatures as much as 20 to 25 degrees above normal for the
inland valleys. The next storm system brings much cooler
conditions by Monday and especially Tuesday. The marine layer and
May Gray makes a return for inland areas as early as Monday with
low clouds limited to the beaches this weekend. Gusty winds will
accompany the storm system for Monday and Tuesday with the
strongest gusts found in the mountains and deserts. Gradual
warming back to near normal for late next week.

&&

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

This weekend...

The building ridge of high pressure peaks in intensity tonight
into Saturday, setting the stage for the hottest day of the year
so far. Ensemble mean guidance is supporting high temperatures in
the Inland Empire reaching 101-103, locally near 105 with highs
near 97 across the San Diego County inland areas, locally 99-101
in valleys. With this, the Heat Advisory has been expanded to
include the San Diego County inland valleys for Saturday
afternoon. These temperatures will come in about 20-25 degrees
above normal for mid May, a stark difference from what was seen
earlier this week when the marine layer was keeping highs in the
upper 60s to low 70s for many. The ridge axis begins to shift
eastward into Sunday, allowing for the beginning of a cooldown,
with highs 5 to 10 degrees cooler than Saturday.

With the persistent subsidence from the upper level ridge, the marine
layer will likely be even lower than this morning/afternoon, but
will likely be a bit more patchy in coverage. For land areas, the
greatest coverage of low clouds for for this morning is expected
for San Diego County from the coast inland to around the mesas
with the fog locally dense near the mesas and other higher coastal
terrain. Less certain is how much deepening and inland spread of
the coastal low clouds will occur for Saturday night into Sunday
morning. The most likely scenario is for the low clouds to return
into portions of the western valleys by Sunday morning ahead of
the next storm system.

Monday and Tuesday...

A large upper level low off the Pacific Northwest coast Sunday
morning moves ashore and digs down through California Monday into
Tuesday. While this system will likely not feature much in the
likes of precipitation, it will bring a sudden drop in
temperatures, a much deeper marine layer, and gusty winds for the
mountains and deserts. As quickly as the temperatures rose late
this week, they will cool just as quickly with the incoming
trough, as high temperatures will fall to be as much as 15 to 20
degrees below average for the mountains as quickly as Tuesday.
High temperatures on Tuesday will range from the lower to mid 60s
near the coast to the 60s for the valleys with the lower deserts
in the mid 70s to lower 80s. Night and morning coastal low clouds
are expected to return to portions of the inland valleys by
Monday morning, then onto the coastal slopes of the mountains for
Monday night and Tuesday. There will be stronger onshore flow for
Monday and Tuesday with stronger and gusty southwest to west
winds for the mountains and deserts. The stronger gusts, to 45 to
55 mph, are expected in the northern Coachella Valley below the
San Gorgonio Pass with isolated gusts to 60 to 70 mph.

Wednesday into Late Week...

The main axis of the upper trough passes by Wednesday morning, and
while weak troughing lingers into late week, Wednesday into
Thursday will be less cool than Thursday, inching closer to near
normal by Friday. For Wednesday and Thursday, the marine layer
won`t be quite as deep, but coastal low clouds will spread into
portions of the inland valleys for Wednesday night into Thursday
morning.


&&

.AVIATION...
092030Z..Coasts/Valleys...Low clouds based at 200-500 ft MSL will
continue to hug the coastline through the afternoon with some areas
partially clearing by early evening. Confidence continues to be low to
moderate on clouds and fog forming at coastal TAF sites by Saturday
morning. Most likely time period with cigs would be from 08-15Z,
highest confidence of formation in San Diego County. Where clouds
with bases 200-500 ft MSL do develop, expect vis to drop to 2-4 sm,
locally lower on elevated surfaces. Similar to today, clouds may linger
at the beaches into the afternoon.

Mountains/Deserts...Mostly clear with VFR conditions through tonight
and Saturday.

&&

.MARINE...
Low clouds and patchy fog will  bring visibilities to 1-3SM over the
waters tonight into Saturday morning and afternoon, locally under
1SM. Please see the Marine Weather Statement (MWSSGX) for more
details. West winds will strengthen by Monday and Tuesday leading to
increased confidence on wind gusts reaching small craft strength across
the outer waters.

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Heat Advisory until 9 PM PDT Saturday for San Bernardino and
     Riverside County Valleys-The Inland Empire.

     Heat Advisory from 10 AM to 9 PM PDT Saturday for San Diego
     County Valleys.

PZ...None.

&&

$$

PUBLIC...Munyan
AVIATION/MARINE...APR