National Weather Service National Headquarters

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

-- Discussion containing changed information from previous version are highlighted. --
000
FXUS66 KSGX 182024
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
123 PM PDT Sun Apr 18 2021

.SYNOPSIS...
-- Changed Discussion --
Santa Ana weather will persist into Monday, but winds will weaken
along the coastal foothills, and cooling will begin along the
immediate coast. It will remain quite warm inland on Monday, with
cooling making better inland progress through midweek. Onshore flow
will strengthen late Monday ahead of another trough dropping south
through Nevada, deepening the marine layer. Expect more clouds, fog,
patchy drizzle, and perhaps some light rain showers Wednesday into
Thursday morning. Temperatures will be below average through
midweek, then rise back to average and above into next weekend.
-- End Changed Discussion --

&&

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

At 1 PM PDT...Skies were clear over SoCal. The offshore sfc pressure
gradient was weakening and wind reports, while gusty in many areas,
including the deserts, were falling below Advisory strength. So the
Wind Advisory has been cancelled. Still, it was very dry, and where
it was breezy, the combination of wind and very low RH was creating
elevated to near critical fire weather conditions in a few spots(See
Fire Weather discussion below). Winds of 20-30 MPH with higher gusts
to around 40 MPH will be confined to the wind-prone pass and
foothill areas for the remainder of the day.

Today will be the warmest day of the week along the coast, even with
a weak sea breeze. On Monday, winds will begin the day weakly
offshore, but turn back onshore and become gusty through the passes
and along the desert slopes later in the day. It will be warmer
tomorrow inland, but coastal areas should begin to cool as marine
air gradually replaces dry, continental air.

For Tuesday through Thursday, a broad trough will become
reestablished over the SW, supporting stronger onshore flow and a
deepening marine layer. Most ensemble members of the CMC/EC/GFS
models have some light precip falling over the coastal basin either
Wednesday or Thursday. Dynamics are weak, so any accumulations will
be light. Once again, some of the lower coastal slopes could see
some of the larger accumulations, due to better convergence in the
shallow moist layer.

As we head into the weekend, a weak ridge develops over the SW and
the ensembles favor at least slight warming over SoCal ahead of
another developing EastPac trough next week as the marine layer
shrinks back toward the Coast. Uncertainty increases considerably
for next week as a number of ensemble solutions of both the
CMC/ECMWF turn wet. The ECMWF deterministic is the most bullish,
indicating a sizable late season storm here. The entire GFS
ensemble spread however remains dry for that period.
-- End Changed Discussion --

&&

.AVIATION...
-- Changed Discussion --
182030Z...Clear skies will prevail through Monday with unrestricted
vis.

Areas of N-NE winds 15-25 knots with local gusts 30-40 knots will
continue from the mountain crests through the foothills and into the
valleys through 22Z with gradually diminishing winds through 02Z
Mon. This will include VCNTY KONT, KCNO, KRAL, KRIV, KAJO. Areas of
MOD up/downdrafts and LLWS will also occur.
-- End Changed Discussion --

&&

.MARINE...
Northwesterly winds will locally gust around or slightly over 20
knots in the outer coastal waters this evening and then again Monday
evening. Otherwise, no hazardous marine weather is expected through
Thursday.

&&

.FIRE WEATHER...
-- Changed Discussion --
Several sites across the Inland Empire and into the San Gorgonio
Pass were hovering near the edge of critical fire weather criteria
at Noon today with RH at about 10% and wind gusts to 35 to locally
45 MPH. These winds will weaken this afternoon, but RH will remain
low.

Some modest RH recovery will occur overnight, and coastal areas will
continue to recover on Monday, while inland areas fall back to or
below 10%. Winds will turn back onshore by midday, and become gusty
from the west through and below the passes, along the desert slopes
and into the deserts. These areas will see elevated fire weather
conditions by late afternoon.

The onshore flow and increasing marine influence will minimize fire
weather conditions along and west of the mountains for the remainder
of the week.
-- End Changed Discussion --

&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
CA...NONE.
PZ...NONE.
-- End Changed Discussion --

&&

$$

PUBLIC/FIRE WEATHER...10
AVIATION/MARINE...Maxwell