007
FXUS66 KSGX 180859
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
159 AM PDT Sat Apr 18 2026

.SYNOPSIS...
Inland areas will warm this weekend while coastal areas begin to
cool on Sunday as onshore flow returns. Onshore flow will begin
to strengthen and spread cooling inland on Monday as a low
pressure system moving into California brings cooler and breezy
conditions for the middle of next week, along with a slight chance
of precipitation Tuesday afternoon into Wednesday morning. Cool
weather and breezy onshore flow persist for the remainder of the
week.

&&

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

Very patchy stratus has developed over San Diego County this
morning with mostly clear skies elsewhere. Expect coverage to
remain sparse under weak offshore flow, clearing by mid-morning.
An upper level ridge moves east across the area today as it
amplifies, bringing warming across the inland areas - as much as
10 degrees warmer than yesterday in the high desert. Highs will be
in the low to mid 70s along the coast, upper 70s to mid 80s for
inland coastal areas and valleys, upper 50s to upper 60s in the
mountains, mid to upper 70s in the high desert, and upper 80s to
around 90 in the low desert. The upper level high shifts further
east and continues to amplify on Sunday, continuing warming in the
mountains and deserts. A return of onshore flow will spread
cooling inland west of the mountains, and bring more widespread
low clouds along the coast tonight into Sunday morning.

Onshore flow strengthens Monday through Wednesday as a large upper
level low gradually progresses inland through California. Gradual
cooling takes place through this period, with highs decreasing to
around 3 to 8 degrees below normal by Wednesday. Gusty onshore
winds develop over the mountains, deserts, and through the passes
each afternoon and evening, peaking on Tuesday as the initial
short wave passes. Wind gusts around 30-45 mph will occur along
the desert mountain slopes, below the passes, and into the deserts
Tuesday, with locally higher gusts below the San Gorgonio Pass.

The upper trough will also bring a slight chance of showers
sometime Tuesday into Wednesday. There are still some differences
in the ensembles with the exact timing of the trough. General
consensus is that we`ll be on the tail end of this system, with
only light precipitation if any. NBM probabilities of measurable
rain (at least 0.01") for the 24 hr period of 5 am Tuesday through
5 am Wednesday range from around 25% for Orange County/far west
Inland Empire and the mountains to 10-15% for the remainder of
the Inland Empire, high desert, and San Diego County coasts and
valleys, and less than 5% in the low desert. Chances of at least
0.10" is around 20% along the south slopes of the San Bernardino
Mountains and less than 10% elsewhere. A second short wave moves
through sometime late Wednesday, but is currently forecast to be
to dry to produce any precipitation.

Upper troughing remains across the Western US for the remainder of
the week, maintaining cooler weather with high temperatures a few
degrees below normal and breezy conditions in the mountains and
deserts each afternoon. The marine layer will also be fairly deep
during this time, but the marine inversion may be weak enough that
low cloud coverage will be somewhat patchy in the coastal areas
and valleys once the main trough axis passes on Wednesday.

&&

.AVIATION...
180000Z...Mostly clear and VFR conditions expected region-wide
through most of tonight. North to northeast winds gusting 20-35 kts
through mountain passes and locally into valleys will continue to
calm through about 02Z. Patchy low clouds around the coast early
Saturday 10-16Z, but any cigs would be brief and isolated, based
around 1000 feet MSL.

&&

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

&&

.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...CSP

NWS San Diego (SGX) Office