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000
FXUS66 KSGX 260357
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
857 PM PDT Thu Apr 25 2024

.SYNOPSIS...
Gusty westerly winds; periods of drizzle or light rain west of the
mountains; and cooler conditions are expected through Friday. A deep
marine layer will result in night and morning low clouds throughout
much of the coastal basin through Friday. The marine layer will
become shallower into the weekend. A gradual warming is expected
over the weekend into early next week.

&&

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

9 PM Update: Satellite depicts low clouds filling back in over
much of the coastal basin, and the 00z Miramar sounding shows a
roughly 5C inversion based near 5000 FT MSL. Clouds will cover
much of the coastal basin this evening through Friday morning with
abundant marine layer moisture and onshore flow in place. The
approach of another, larger 500mb trough will not only support
additional light showers/drizzle tonight, but also maintain gusty
onshore winds. The strongest winds, per surface observations, are
occurring in the San Gorgonio Pass near Whitewater, where gusts of
55-65 mph continue this evening. The forecast appears on track and
no changes were made to the gridded forecasts or any Wind Advisory
products.

From Previous Discussion:

Visible satellite at 130 PM this afternoon was showing widespread
cloud coverage across the coastal basin. Clear skies were prevailing
in the mountains and deserts. The marine layer will remain deep into
Friday as a low pressure system digs south into the Great Basin.
This will keep the atmosphere unsettled, with periods of passing
shortwaves moving through the mean flow ahead of the core of the
system. The passing shortwaves are expected to generate areas of
scattered light showers or drizzle as they interact with deep marine
layer moisture tonight into early Friday morning. As the core of the
low digs into the Great Basin Friday afternoon and evening, periods
of light showers are expected to develop. Coast and valley areas in
San Diego county as well as the coastal mountain slopes are the most
likely places to see a shower. Most areas will see 0.05 inches of
rain or less, but a few locations may accumulate up to 0.15 inches
if showers train across that particular area. 0.10 to 0.35 inches of
rain are possible in the mountain foothills. Light snow
accumulations are possible above 7000 ft Friday evening.

Periods of gusty westerly winds will continue over the mountains and
into the deserts through Friday night. Peak gusts for this afternoon
into early Friday morning will be mostly 50 to 60 mph on the desert
mountain slopes. Gusts 40 to 50 mph possible in the deserts. Local
gusts up to 70 mph possible through the San Gorgonio Pass near
Whitewater. Gusty winds will continue for Friday afternoon into
early Saturday. There is a potential for more widespread coverage of
stronger wind gusts on Friday as a low pressure system moves into
the Great Basin and east into the Four Corners region. Peak Gusts of
50 to 65 mph are expected on the desert mountain slopes. Gusts in
the deserts will peak at 40 to 50 mph. There will also be the
potential for gusts 70 to 75 mph in wind prone locations like
through the San Gorgonio Pass.

Widespread below average high temperatures are expected tomorrow and
Saturday. By Sunday, highs will warm to near average, with some
locations still a degree or two cooler than average for this time of
year. Further warming is expected into early next week. By the
middle of next week, some uncertainty develops in the upper level
pattern, with some ensemble solutions showing troughing while others
maintain a weak ridge. This introduces uncertainty into the
temperature forecast, with the potential for cooler conditions to
return. This uncertainty also impacts the depth of the marine layer.
Current forecast follows NBM with a few degrees of cooling on
Thursday with a shallower marine layer for early next week, slowly
deepening into the middle to end of next week.

&&

.AVIATION...
260345Z...Coast/Valleys/Foothills...BKN-OVC cigs will continue to
fill into this region tonight. Cigs near 4000-6000 ft MSL will lower
2000-4000 ft MSL, locally near 1500 ft MSL between 12-20Z. VCSH and
DZ will occur for areas near the coast and portions of San Diego
County 08Z-18Z Fri. Vis to 3-5SM with higher terrain obscured
tonight into Friday morning.

BKN cigs near 2500-3500 ft MSL throughout much of the day on Friday
across San Diego County, with a better chance of SCT-BKN clouds in
northern areas by Friday afternoon. W winds increasing after 22Z
Friday with winds 20-30 kts.

Mountain Ridges/Deserts...Areas of west winds with surface gusts 25-
40 kt through tonight. Occasional LLWS and rotors near lee slopes
and adjacent deserts, such as vcnty KPSP, along with MOD to STG
up/downdrafts. Areas of reduced vis 3-5SM in BLDU in deserts. Winds
becoming more widespread and stronger after 18Z Friday where chances
are moderate to high in seeing wind speeds greater than 45 kts.

&&

.MARINE...
Stronger winds and higher seas will generate hazardous boating
conditions Friday through early Saturday, especially beyond 15 NM
offshore. A few gales are possible Friday night near San Clemente
Island. The Small Craft Advisory contains further details. Calmer
winds and seas are expected this weekend into 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...Beach Hazards Statement from Friday afternoon through Saturday
     morning for Orange County Coastal Areas-San Diego County
     Coastal Areas.

     Wind Advisory until 11 PM PDT Friday for Apple and Lucerne
     Valleys-Coachella Valley-Riverside County Mountains-San
     Bernardino County Mountains-San Diego County Deserts-San
     Diego County Mountains-San Gorgonio Pass Near Banning.

PZ...Small Craft Advisory from 1 PM Friday to 7 AM PDT Saturday for
     Coastal Waters from San Mateo Point to the Mexican Border
     and out to 30 nm.

     Small Craft Advisory from 3 AM Friday to 11 AM PDT Saturday for
     Waters from San Mateo Point to the Mexican Border Extending
     30 to 60 nm out including San Clemente Island.


&&

$$

PUBLIC...Adams (Update)/CO
AVIATION/MARINE...APR