591
FXUS66 KSGX 272053
AFDSGX
Area Forecast Discussion
National Weather Service San Diego CA
153 PM PDT Mon Oct 27 2025
.SYNOPSIS...
Offshore flow and strengthening high pressure aloft will bring
warming through Wednesday with periods of gusty Santa Ana winds
along and below the coastal slopes of the mountains for tonight
into Wednesday with the stronger gusts to 35 to 45 mph. High
temperatures 15 to 20 degrees above normal expected Tuesday and
Wednesday afternoon. Weak onshore flow will bring less hot
conditions inland for Thursday and Friday with high temperatures
for next weekend at least a few degrees warmer as high pressure
aloft strengthens and another weak offshore event appears
possible.
&&
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
Today through Wednesday...
As the trough currently over Idaho digs southeastward today,
building high pressure across the Great Basin will strengthen the
offshore pressure gradient. North to northeasterly flow is set to
begin this afternoon across the deserts and desert slopes, while
onshore flow prevails today for the coasts and valleys. This will
likely inhibit the marine layer, with only a few clouds possible
along the coasts tonight. As inland high pressure builds, the
offshore gradient is set to peak on Tuesday, resulting in in weak to
locally moderate strength Santa Ana winds, with strong gusts
primarily focused within and below main mountain passes. Wind gusts
here could gust up to 35 to 45 mph on Tuesday afternoon, with 25-35
mph gusts stretching into the Inland Empire, the Santa Ana
Mountains, and the inland valleys of San Diego County. High pressure
in the Great Basin slides east heading into Wednesday, and while
offshore flow should persist through late Wednesday, wind gusts
should be notably weaker than Tuesday.
Meanwhile, a building ridge paired with the compressional effects of
the downslope, offshore winds and a lack of a marine layer will
culminate in a substantially warmer day on Tuesday compared to
today. Afternoon temperatures are expected to soar into the low to
mid 90s across inland portions of Orange/San Diego counties and
the Inland Empire, coming in about 13-18 degrees above normal for
late October. Despite weaker offshore flow Wednesday, continued
dry conditions and the upper level ridge keeps temperatures hot,
even a degree or two warmer than Tuesday. With this, widespread
moderate HeatRisk is still expected across Orange County inland,
San Diego County valleys, and the Inland Empire, and the Heat
Advisory currently in effect for Tuesday into Wednesday remains on
track. The offshore flow brining in the hot and dry desert air
will also send afternoon humidity into the low teens Tuesday and
Wednesday afternoon. This when combined with the Santa Ana winds
will bring elevated fire weather conditions, and locally critical
conditions during the periods of strongest winds in the afternoon
within wind- prone mountain passes.
Thursday into Late Week...
The offshore pressure gradient relaxes late Wednesday into Thursday,
with onshore flow reestablished for the coasts and valleys by
Thursday afternoon. The absence of offshore flow allows
temperatures to cool some for Thursday, albeit still 5-10 degrees
above normal. Weak ridging remains in place into the end of the
week, keeping the marginally above normal warmth in place. The
marine layer looks to return, at least partially, by Thursday
morning. Another weak offshore wind event is possible this
weekend, which could bring another period of warmer and drier
conditions.
&&
.AVIATION...
262000Z...Coast/Valleys...Mostly clear through the afternoon hours
with lingering HZ and vis 3-5sm across the Inland Empire. Confidence
now moderate to high of BKN cigs near 800-1200 ft MSL returning to
VCTY KSAN/KCRQ 06-16z Tue. Cigs becoming more intermittent after 12Z
Tue. Lower confidence in these cigs impacting VCTY KSNA. N/E winds
with gusts 20-30 kts increasing across parts of the Inland Empire
downwind of the Cajon / Banning Passes after 12Z Tues will lead to
MOD UDDFS at times.
Mountains/Deserts...Clear and VFR conditions today and tonight. N/E
wind gusts 20-35 kts around coastal facing slopes and passes after
12Z Tue, leading to MOD UDDFS.
&&
.MARINE...
No hazardous marine conditions are expected through Friday.
&&
.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Heat Advisory from 11 AM Tuesday to 7 PM PDT Wednesday for
Orange County Inland Areas-San Bernardino and Riverside
County Valleys-The Inland Empire-San Diego County Valleys.
PZ...None.
&&
$$
PUBLIC...Munyan
AVIATION/MARINE...APR NWS SGX Office Area Forecast Discussion