Ladera Ranch, California Weather Forecast Discussion

442
FXUS66 KSGX 220946
AFDSGX
Area Forecast Discussion
National Weather Service San Diego CA
246 AM PDT Mon Sep 22 2025
.SYNOPSIS...
Widespread clouds and scattered light showers will continue
this morning, gradually shifting south and east into Monday and
out of the area by early Monday afternoon. Precipitation Chances
decrease for Monday night into Tuesday but could return for
Tuesday afternoon into early Wednesday, along with a slight chance
of thunderstorms mainly for areas north of San Diego County.
Drier weather returns for early Thursday, but then increasing
chances of precipitation will occur by later in the evening and
going into Friday through Saturday. By Sunday, the disturbance
will begin to move east and out of the region, with slight warming
and drying conditions going into the early part of next week.
Temperatures will overall remain right around, or slightly below,
the seasonal average this time of year with decreasing coastal low
clouds throughout the week.
&&
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
Today through tomorrow...
Currently, night fog imagery reveals that most of the marine layer
has filled in over the inner waters of the SoCal bight, and has
extended inland over portions of Orange and San Diego counties.
There are also showers falling from mid level clouds streaming
across the region due to troughing over the eastern Pacific waters
west of California, which is continuing to deepen, and has allowed
for subtropical moisture to be advected up from the southwest and
providing us with precipitation the morning. Some of these showers
have been producing some lightning with just enough upper level
difluence over the region to provide the instability needed for
there to be enough vertical extent with some of the embedded cells.
At the moment, the main brunt of the moisture is mostly south of
the CWA, over northern Baja California, Mexico. By later today,
this feature will become cutoff, with the upper level low
associated with this positioned directly to the west-southwest of
San Diego at roughly 500 nm (given the consensus of the
deterministic models) and closing off with heights of around
575-577 dm, depending on which model resolves this feature the
best. This will allow for some of the subtropical moisture to be
advected up over the region from the southwest throughout the day.
However, given that there will be very weak instability with
this, it is more likely that any precip will be more stratiform in
nature and in elongated bands extending from southwest to
northeast, and only amount to generally light precip with amounts
of less than a tenth of an inch for most locations. There could be
slightly higher amounts over the mountains with the aid of
orographic lifting to help squeeze out a little more moisture.
Given that there is also just enough instability over the
mountains, there exists a slight chance of a thunderstorm
developing within the embedded bands by later this afternoon. If
this occurs, it may allow for locally higher amounts of possibly
more than a quarter of an inch for some locations, such as Palomar
Mountain again, or possibly over the deserts where there is
better instability available. The main The marine layer will
likely struggle to fill back in again later this evening, given
the extensive mid-high level cloud coverage overhead.
By tomorrow, the low will continue to meander and slowly transition
towards Socal, which will allow for a better chance of more
widespread precipitation. There could also be a few embedded
thunderstorms over the mountains, due to orographic lifting, as well
as possibly over the desert where there is increased instability. If
this occurs, then there could be some areas which receive locally
higher rainfall amounts of possibly greater than a quarter of an
inch again tomorrow. Given where the position of the U/L low will
be, and all of the CWA being within the relatively unstable side,
the best chance for showers and thunderstorms (some possibly being
on the heavy side) during the afternoon on Tuesday. The best
instability that CAMS are displaying with mixed layer CAPE during
the afternoon still looks to be around 1000 J/kg over some of the
mountains, and better moisture to the north will allow for there to
be a slightly higher probability of a storm developing over the San
Bernardino Mountains. Temperatures will also remain on the cooler
side with the cut-off low over the region, and even slightly below
the seasonal average for this time of year, especially for the
inland areas and deserts. Amounts will generally be less than a
tenth, although, there could be higher amounts along the west-facing
slopes of the foothills, and over the mountains, where there could
be amounts ranging from 0.10-0.25 inches. A storm may also result in
locally higher amounts. The marine layer will also be disrupted by
this, and will attempt to reform and move back inland by much later
in the night, with some areas of patchy fog being possible along
some of the coastal foothills and within valleys, especially where
precip as fallen during the day.
Wednesday through the upcoming weekend...
By Wednesday, the U/L low is going to begin to propagate more
towards the north, and then back towards the southeast. This will
allow for a bit of a `lull` in terms of the chances of precipitation
as the region becomes more "dry-slotted", and temperatures will also
be slightly warmer as well. That being said, there does still appear
to be enough instability in place, and along with orographic lifting
playing in, to see the development of a few showers, and possibly a
thunderstorm or two, over the mountains, which would have a southern
movement giving the mid-level steering flow coming from the
north. On Thursday, the consensus of the latest guidance has the
U/L low retrograding back towards the southwest on Thursday and
into Friday, with an increasing chance of showers and
thunderstorms, which will carry into Saturday. Depending on how
the U/L low evolves and where the displacement of the subtropical
moisture source to the south, along with the modification as it is
parked over the Mojave Desert and residence time allows the low
to dry out more, will determine how much moisture is available and
how much shower/thunderstorm activity there will be. As of right
now, it does appear that the chance will be better to see
measurable precipitation by later on Friday and going into
Saturday. This will all be depended on where this cut-off low
decides to transition. By Sunday, the U/L low should begin to
finally move out of the region as it continues to progress
eastward, which slightly drying and warming conditions expected.
High temperatures will remain on the cooler side as overall
troughing remains persistent over the region going into the
following weekend, and ensembles also confirm this, with the
relatively cooler and drier conditions locked in through then, and
then slight warming going into the early part of next week as
more ridging upstream begins to slowly propagate towards the
region.
&&
.AVIATION...
220930Z....Coast...Patchy low clouds and fog will produce
intermittent cigs at around 600-800 feet MSL and vis 3-6SM through
16Z. Patchy and intermittent low clouds and fog at similar levels
will redevelop after 03Z tonight into Tuesday.
Otherwise, BKN clouds around 10000 feet MSL will continue to produce
-SHRA over southern and eastern areas this morning, but eventually
move out to the east. Lingering isold SHRA/TSRA with briefly lower
bases and vis over eastern San Diego County 18-01Z today. Mostly
clear skies over inland areas after 01Z.
&&
.MARINE...
The chance of thunderstorms today and Tuesday are extremely low. 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...Stewey
AVIATION/MARINE...MM

NWS SGX Office Area Forecast Discussion