212
FXUS66 KSGX 201047
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
347 AM PDT Fri Sep 20 2024

.SYNOPSIS...
A low pressure system moving across southern California will
bring a slight chance of mostly light showers this morning. There
are greater chances for showers along with a chance of
thunderstorms for this afternoon and early evening for
southwestern San Bernardino and western Riverside Counties with
the greatest potential for any heavier rainfall in the San
Bernardino Mountains. For Saturday through Monday, dry with a
warming trend with high temperatures warming to around 5 degrees
above average for inland areas on Monday. Generally fair weather
with seasonal temperatures will continue for Tuesday through
Thursday, but with greater spread in the temperature guidance for
the coast and valleys.

&&

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

.SHORT TERM (Today through Sunday)...
A closed low pressure system will move across southern California
today and into Arizona tonight. It will bring some light showers
from the coastal waters into the coast and valleys in San Diego
County this morning.

As the upper center moves eastward today, there is greater
potential for showers along with a chance of thunderstorms to
movement toward the southwest for this afternoon and early
evening across southwestern San Bernardino and western Riverside
Counties with the greatest potential for any heavier rainfall in
the San Bernardino Mountains.

Today will remain cooler with well-below average high
temperatures, as much as 15 to 20 degrees below average for the
mountains and inland valleys, with high temperatures for the
Inland Empire mostly in the 70s.

Dry weather with warming is expected for the weekend. On Saturday,
greater warming is expected for the mountains and deserts with
slower warming for the coast and valleys. Warming will continue on
Sunday with the greater warming for the coast and valleys. With
the warming, high temperatures on Sunday will return to around
average with high temperatures for the Inland Empire in the mid
80s to mid 90s and for the lower deserts around 100.

&&

.LONG TERM (Monday through Thursday)...
The warming is expected to continue into Monday with high
temperatures for inland areas around 5 degrees above average,
mostly in the 90s for the Inland Empire and around 105 for the
lower deserts.

Generally fair weather with seasonal temperatures will continue
for Tuesday through Thursday, but with greater spread in the
temperature guidance for the coast and valleys.

&&

.AVIATION...
200900Z...Coast to Mountain Slopes...Low stratus remain in place
this morning, with the greatest coverage against the coastal mountain
slopes, the eastern Inland Empire, and San Diego County
hills/valleys, while the coastal basins are somewhat patchy. Bases
are predominantly 3500-4500ft MSL, but intermittent CIGs around 1500-
2500ft MSL are possible at times until 16-18z, especially along the
coasts. Clouds generally become SCT or less for most after 18z,
while the coastal slopes may see higher coverage linger into the
afternoon. Stratus rebuilds again between 03-06z this evening, with
bases around 1500-2500ft MSL.

Patchy, intermittent -RA or -DZ is possible along the coast and up
against the coastal mountain slopes at times until 18-21Z Fri. Vis
reductions of 4-6 SM and locally lower cigs possible in areas of -
RA/DZ. From 20-02Z this afternoon/evening, there is a 25-45% chance
of TSRA over the eastern Santa Ana Mtns and Inland Empire. Erratic
winds, local up/downdrafts, and reduced vis in locally heavy rain
expected near thunderstorms.

Mountain Ridges to Deserts...Mostly clear skies with generally
unrestricted VIS through the late morning. 50-60+% chance for RA and
TSRA over the San Bernardino mtns, Riverside mtns, and High Desert
20Z-02Z this afternoon/evening. Erratic winds, local up/downdrafts,
and reduced VIS in locally heavy rain expected near thunderstorms.

&&

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

&&

.HYDROLOGY...
A low pressure system moving across southern California will bring
a slight chance of mostly light showers this morning. There are
greater chances for showers along with a chance of thunderstorms
for this afternoon and early evening to move southwestward across
southwestern San Bernardino and western Riverside Counties. The
greatest potential for any heavier rainfall is in the San
Bernardino Mountains with rainfall of one-half to three-quarters
of an inch possible with isolated hourly rainfall to one-half
inch.

The most likely location for any mud and debris flows from recent
fires would be with the Line Fire in San Bernardino County. While
much of the higher resolution guidance shows peak hourly rainfall
rates to around one-half inch, there is greater spread in the
timing of any heavier rainfall during the afternoon. Some of
guidance has the peak earlier in the afternoon while some of the
more recent HRRR guidance is later in the afternoon, toward 4 or 5
PM.

The local NAM-bounded WRF from late Thursday afternoon had the
earlier timing with peak hourly rainfall rates in the early
afternoon. Since there`s been an overall slight slowly of this
system over the last day or so, it will be interesting to see if
there is a shift toward later in the afternoon with the next local
WRF run from late Thursday evening that should be available in
the next few hours.

&&

.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...17
AVIATION/MARINE...Munyan