357
FXUS66 KSGX 040935
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
235 AM PDT Sat May 4 2024

.SYNOPSIS...
Mostly cloudy cool weather will prevail this weekend with gusty
winds in the mountains and deserts and periods of showers over and
west of the mountains. Southwest to west winds will strengthen
through the day today, peaking tonight and early Sunday. Patchy
drizzle may occur this morning, but the best chances of
accumulating rain will be tonight and early Sunday. Dry and
warmer conditions will prevail Monday through most of next week.

&&

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

.SHORT TERM (Today-Monday)...
Marine layer low clouds have filled in west of the mountains and
have spread into the Cajon Pass. Elsewhere skies are clear. The
marine layer cloud deck may be thick enough for some patchy light
drizzle again this morning, though little in the way of
accumulation is expected.

A large upper level low currently positioned off the Oregon coast near
44.2N, 131.5W will progress east-southeast into the northern Great
Basin this weekend. The trough axis and associated surface cold
front will pass through So Cal tonight into Sunday. Both the GFS
and EC show IVT of over 400 kg/m/s and a quick-hitting weak
atmospheric river tonight into Sunday morning in mostly west-
southwesterly flow. Despite the higher IVT, most of the moisture
will be confined below about the 750-800 mb level. Given this and
the short duration, rainfall amounts will be somewhat limited -
generally less than 0.15 inch for the coasts/valleys with local
amounts around 0.25 inch near the foothills. Orographics will
enhance precipitation along the coastal slopes of the mountains
with amounts of 0.25-0.50 inch, upwards of 0.75 inch on the
southwest facing slopes of the San Bernardino Mountains. Amounts
in the high desert, if any, will be a couple hundredths of an
inch, with no precipitation expected in the low deserts. Precipitation
will come to an end by early Sunday afternoon. Snow levels will
begin near 7500-8000 ft tonight, falling to around 5500 ft behind
the cold front as precipitation tapers off. Any snow accumulation
will be limited to an inch or less.

In addition to precipitation, this system will generate breezy
southwest to west winds across the mountains and deserts this
afternoon into Sunday, strongest this evening into tonight.
Highest wind gusts will be around 50-60 mph along the desert
mountain slopes and locally into the deserts with isolated gusts
to around 70 mph through the San Gorgonio Pass. Winds slowly
weaken late Sunday afternoon into Monday morning. Another round of
weaker but still gusty west winds will occur Monday afternoon and
evening.

Significant cooling occurs through the weekend. Today, highs will
be around 3-7 degrees below normal for most areas, near normal in
the low deserts. Sunday is even colder with highs around 15-20
degrees below normal inland and 5-10 degrees below normal near the
coast. This puts us at highs in the 60s for the coastal
areas/valleys and high deserts, 40s in the mountains, and 70s to
around 80 in the low desert. Temperatures rebound quickly for
Monday, though highs will remain a few degrees below normal.

&&

.LONG TERM (Tuesday-Friday)...
The slow warming trend continues into Tuesday as the upper low
moves out. Beyond Tuesday is a little less uncertain, however, as
ensemble solutions begin to diverge with regards to a second low
dropping out of Canada and setting somewhere into the Western US
while a ridge sets up to our west. For Wednesday the ensembles are
pretty much split half and half on warmer vs cooler scenarios. By
Thursday, the cooler scenario with the low retrograding much
further SW is the outlier containing only 7 percent of global
ensemble members. Given the large uncertainty left NBM for
temperatures which shows a very subtle warming trend through the
week. This uncertainty also has implications on the depth of the
marine layer and the strength of the marine inversion which would
affect how far inland any clouds would extend and how much
clearing we would have each day.

&&

.AVIATION...
040835Z...Coasts/Valleys/Foothills...Low clouds cover the region
west of the mtns, with bases 1800-2200 FT MSL and tops to 3000 ft
MSL. VIS reduced to 1-3SM where low clouds and terrain intersect,
obscuring higher terrain. Expect clearing 17z-20z inland, with
partial clearing near the coast and intermittent CIGs into the
afternoon.

Elsewhere...Clear skies with unrestricted VIS this morning, with
increasing high clouds AOA 15,000 FL MSL later today.

Mountains/Deserts...W-SW winds developing after 20z, with the
strongest winds after 00z Sun. Expect W-SW winds 20-35 kt with gusts
of 45-60 kt. Areas of MOD-STG up/downdrafts and LLWS over/east of
mtns.

&&

.MARINE...
No hazardous marine conditions are expected through this morning.
Gusty northwest wind gusts of 25 to 30 knots will occur this evening
through Sunday evening, which will generate hazardous boating
conditions, especially in the outer waters. Northwest wind gusts up
to 20 knots will be possible over the outer waters each afternoon
and evening for Monday through the middle of next week.

&&

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


&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Wind Advisory from noon today to 8 PM PDT Sunday for Apple and
     Lucerne Valleys-San Bernardino County Mountains-San
     Gorgonio Pass Near Banning.

     Wind Advisory from 3 PM this afternoon to 8 PM PDT Sunday for
     Coachella Valley-Riverside County Mountains-San Diego
     County Deserts-San Diego County Mountains.

PZ...Small Craft Advisory from 3 AM to 10 PM PDT Sunday for Coastal
     Waters from San Mateo Point to the Mexican Border and out
     to 30 nm.

     Small Craft Advisory from 6 PM this evening to 3 AM PDT Monday
     for Waters from San Mateo Point to the Mexican Border
     Extending 30 to 60 nm out including San Clemente Island.


&&

$$

PUBLIC...SS
AVIATION/MARINE...PG