Area Forecast Discussion
Issued by NWS San Diego, CA

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000
FXUS66 KSGX 220425
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
925 PM PDT Thu Mar 21 2024

.SYNOPSIS...
Weak high pressure aloft will bring dry weather Friday with morning
marine layer clouds dissipating through midday. Over the weekend a
trough of low pressure will bring showers, colder weather, and gusty
west winds. The storm moves east Monday followed by dry and
warmer weather Tuesday and Wednesday. Cooler Thursday as another
trough approaches the West Coast.

&&

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

.SHORT TERM (Tonight-Sunday)...
Marine layer low clouds were redeveloping along the coast this
evening with scattered high clouds elsewhere. The 00Z NKX sounding
shows the marine inversion based near 1700 ft MSL, down slightly
from 2000 ft MSL this morning. Low clouds will spread into the
western valleys overnight, clearing to the coast by late Friday
morning. It will be a few degrees cooler on Friday as the upper
level ridge of high pressure shifts east and weakens and a upper
level low approaches the West Coast.

A short wave moving through the mean trough passes through
Southern California on Saturday. This will bring increasing west
winds with gusts 50-60 mph on the desert mountain slopes through
the weekend, cooler weather, and showers mainly along and west of
the mountains. While exact timing is uncertain, it looks like
showers will first move in sometime Saturday morning or early
Saturday afternoon, becoming slightly heavier and more widespread
during the afternoon, then tapering off to more isolated to
scattered showers in the evening as the trough passes. Snow levels
will begin near 6500-7000 ft Saturday morning, falling to around
5500 ft Saturday evening.

The main upper low drops southeast through interior CA on Sunday
with a positively tilted trough passing through So Cal. This will
bring colder air with snow levels dropping to around 4500-5000 ft
by Saturday night. This colder air aloft will aid in instability
with a 15-20% chance of thunderstorms Saturday night and Sunday
for areas along and west of the mountains. The trough moves off to
the southeast Sunday night with showers gradually coming to an
end. The track of the low and attendant trough/upper level flow
will favor San Diego County in terms of rainfall on Sunday,
leading to higher rainfall totals overall.

In terms of rainfall amounts, there is around a 30-60% chance of
at least 0.25 inch and a 15-40% chance of at least 0.50 inch of
storm total rain for the coasts and valleys, with the highest
chances in San Diego County. For the mountains, there is a 25-50%
chance of at least 0.50 inch and a 10-30% chance of at least 1.00
inch of rain/liquid-equivalent, with the highest chances along the
coastal slopes of the San Diego County Mountains. Any
accumulation in the deserts will be less than 0.10 inch. Up to 2
inches of snow is possible between around 4800-6500 ft, 2-6 inches
of between 6500-8000 ft and 8-12 inches above 8000 ft.

This will also be a chilly first weekend of spring with high
temperatures around 10-15 degrees below normal on Sunday and as
much as 15-20 degrees below normal on Sunday, with the greatest
departures from normal in the mountains.

&&

.LONG TERM (Monday-Thursday)...
Dry northwest flow prevails on Monday with high temperatures
several degrees higher than Sunday, but still around 5-10 degrees
below normal. A very weak trough passes by to the northeast on
Tuesday. Ensembles are showing very light precipitation Mon
night/Tue morning with this wave and whatever residual boundary
layer moisture remains, mainly in San Diego County, but dry
weather elsewhere. It could end up being more of a marine layer
drizzle situation. Otherwise continued minor warming Tuesday and
Wednesday under weak transitory ridging.

There is the potential for another trough to move through sometime
Wednesday night into Thursday, though timing is still uncertain.
This could bring additional light precipitation, but for now
rainfall probabilities remain below 20%.

&&

.AVIATION...
212000Z...Coasts/Valleys...SKC conditions will continue through the
daylight hours. Low clouds will push ashore and locally inland after
03-05Z Friday, although not as far inland. Bases/vis should be
similar to or slightly lower than ceilings this morning at around
1000ft MSL.

Mountains/Deserts: Mostly clear skies with unrestricted VIS today
and tonight, but with some cumulus buildups mainly over the
mountains at around 9000 feet MSL 20-01Z.

&&

.MARINE...
No hazardous marine conditions are expected through Saturday
morning. Strong winds will generate hazardous conditions for
Saturday afternoon through Monday. Strongest winds, including gales,
and highest seas are expected Sunday.

&&

.BEACHES...
Large short-period swell from the west-northwest will arrive early
Sunday, peak Sunday night, and subside Monday. This storm swell
could produce breaking surf of 8-10 feet Sunday night, highest in
southern San Diego County.

&&

.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...SS
AVIATION/MARINE/BEACHES...PG


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