976
FXUS66 KSGX 011605
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
905 AM PDT Sun Jun 1 2025

.SYNOPSIS...
An area of low pressure to the south will bring a chance for
showers and thunderstorms through this evening. Cooler weather
with highs near normal will occur through much of the upcoming
week. By Monday, quieter weather with drier conditions will
continue into the following weekend.

&&

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

.Morning Update (238 AM Sunday)...
The low to the south is starting to move ashore across northern
Baja California this morning. The eastern portion of the system
continues to bring in subtropical moisture to portions of SE
California and Arizona. Per latest model guidance this morning,
this trend looks to continue throughout the day and evening,
keeping the most robust part of the system to the east. With that
said, the majority of the rainfall that occurs today will be
across the RIV/SD Co mts into the lower deserts, with a lesser
chance across valleys west of the mountains. Coastal and western
valleys may receive sprinkles/light showers. Thunderstorm chances
will continue today as well in these areas, where a storm may
drift far enough west to reach parts of the San Diego Co valleys.
Some storms may produce hourly rain rates near one half inch. Rap
around moisture from the system will be lighter by tonight.
Humidity will stick around again today, but drying will slowly
occur by Monday, moreso into Tuesday and onward.

.Previous Discussion...

Today through tomorrow...

A cut-off upper level low, which has tapped into tropical
moisture from Alvin from the south, is influencing the region
with weak to moderate instability aloft in the mid to upper
levels. It will be conditionally unstable enough, with the HRRR
showing values of MUCAPE increasing to over 1000 J/kg for some of
the mountainous areas by later this afternoon, which will likely
lead to the development of a few thunderstorms, especially over
the mountains and east-facing slopes of the deserts in San Diego
County. This is in part due to the southeasterly flow around the
U/L low, which will be increasing in the mid levels throughout the
day and orographic lifting. This will help to induce convection
with upsloping, with areas such as Jacumba and Boulevard (or
within the vicinity) likely getting some decent rainfall amounts;
possibly exceeding a half an inch by later this afternoon with
daytime heating allowing for the development of heavier showers
and storms possible over these locations. These areas will have a
higher probability of seeing storms today, of 50 to 70 percent,
and then this tapers off to around a 20 percent probability going
north and west to the coastal areas of San Diego and Orange
counties. Other areas, such as the San Bernardino Mountains, will
also have a better chance of receiving higher rainfall amounts of
possibly a half an inch or locally greater. The deserts will also
have a better chance of receiving precip, given the set up and
orientation of mid-level flow coming out of the SE. It will be
notably cooler today, given the lower heights and extensive cloud
coverage, and much closer to the seasonal average for this time of
year.

Models have been tightening up with the progression of this U/L low
is it continues to propagate towards the northeast by later in the
day. The position of the low by later in the day will not be as
favorable for San Diego proper, given that it will be located
underneath the convergent quadrant of the U/L low. Despite this,
there could be enough of a push as winds at the 700 mb level will be
jamming at roughly 20 to 30 kts out of the east-southeast, which may
allow for some of these storms forming over the mountains to push
off, at least move over into the inland areas, but also could
impact some of the coastal areas with storms by later in the day.
This is all depended in where the embedded waves and areas of PVA
will be positioned around the U/L low at the time that it begins
to transition NE`ward as it is "kicked" by another U/L low moving
down from central California as the trough further deepens. This
secondary U/L low could also help to play a role in keeping the
chance of precip going into tomorrow, with the threat of storms
developing again over the mountains tomorrow afternoon.

Tuesday through next weekend...

The general consensus of ensemble members and deterministic models
alike keep the longwave trough in place over the western states,
with only some weak ridging building back in towards the end of the
week, which will allow for a gradual warmup. For Tuesday and
Wednesday, there could be just enough instability from the secondary
U/L low nearby to allow for an isolated shower or storm to develop
during the afternoon over the mountains, otherwise, with will be
mostly clear with high pressure conditions in place. The marine
layer will likely be more displaced for the next couple of days, due
to the U/L disturbance overhead, although it should become more well
defined and persistent for the coastal areas by later in the week as
onshore flow becomes more predominant. Temperatures will remain near
the seasonal average going into next weekend.

&&

.AVIATION...
011530Z...Coasts/Valleys...A few light showers are moving across
Southern California currently while low clouds have mostly cleared
offshore. Prevailing SCT-BKN high clouds 10,000-20,000ft MSL through
today. Iso TSRA are possible for the far eastern valleys and
foothills, primarily after 18Z today, with -SHRA or VCSH likely for
most of the day. SHRA/TSRA chances along the coasts fall after 02Z
Monday while chances in the valleys and foothills falls after 09Z
Monday. More uniform low clouds will move 15-20 miles inland after
06Z Mon, based 800-1200ft MSL, clearing by 16-17Z Monday.

Deserts/Mountains...SCT-BKN high clouds at 10,000-20,000ft MSL
prevail today. Iso-Sct TSRA possible generally after 18Z today with
the greatest coverage over the mountains. Brief outflow gusts over
25-30kts possible with any developing SHRA or TSRA. Near zero VIS
possible in any storm with heavy rain, along with erratic and gusty
winds. TSRA chances diminish after 03Z Monday, with lingering
showers tapering off by 12Z Monday.

&&

.MARINE...
Chance of showers (20-35%) today across the coastal waters, with a
low chance for thunderstorms around 5-10% this afternoon. Otherwise,
no additional hazardous marine conditions are expected through
Thursday.

&&

.BEACHES...
A long period south swell will build into the region today, leading
to elevated surf for south and southwest facing beaches of 4 to 6
feet with sets to 7 or 8 feet possible. This will result in higher
rip current risk and locally hazardous swimming conditions. Surf
peaks Monday and gradually diminishes Tuesday through Wednesday. A
Beach Hazard Statement is in effect and contains more information.

&&

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


&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Beach Hazards Statement through Tuesday afternoon for Orange
     County Coastal Areas-San Diego County Coastal Areas.

PZ...None.

&&

$$

UPDATE...APR
PUBLIC...Stewey
AVIATION/MARINE/BEACHES...Zuber