236
FXUS66 KSGX 131929
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
1229 PM PDT Fri Mar 13 2026

.SYNOPSIS...
The ridge of high pressure over the region will weaken some over the
weekend, where slight cooling will take place with a deeper marine
layer near the coast. The ridge of high pressure will reamplify by
next week, leading to a prolonged heat wave. This event will
encompass temperatures of 20 to potentially up to 30 degrees above
normal for this time of year, leading to moderate to high heat risk.

&&

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

A 588 dm high is maintaining its strength over the eastern Pacific.
This hot air mass will give another very warm day out there with
temperatures 15-20 degrees above normal. The places that will see
some better relief from the hottest temperatures will be at the
coast and higher elevations over 5,000 feet. The ridge will weaken
some by this weekend, along for greater onshore flow and the marine
layer to deepen slightly. This will give the chance for low clouds
and fog to form near the coast by early Saturday morning (around a
20% chance at San Diego). Saturday will be the coolest day over the
next week, though highs will still be near 10 to 15 degrees above
normal. As onshore flow takes hold, there is near a 50-50 chance to
see wind gusts over 30 MPH across mountain desert passes into the
high desert by Saturday afternoon. The marine layer will be its
deepest by Sunday morning with low clouds and patchy fog moving in
from the coast to about ten miles inland.

The high off the coast will begin reamplify on Sunday, where higher
pressure heights near 585mb move into the area. This will kickoff
a major heat wave for the region as we move into the upcoming week.
Sunday temperatures will warm another 5 to 10 degrees across inland
valleys west of the mountains, about the same from Saturday
everywhere else. Chances are low to moderate to see areas of the
northern Inland Empire go over 95 degrees on Sunday.

The center of the high slowly moves toward the region by Monday
through Wednesday, then moves slowly eastward into Arizona by later
in the week. This is a very hot air mass with temperatures at 850 mb
nearing 25C, which is about 15C above normal for this time of year,
very hot! Due to this prolonged heat event, an Extreme Heat Watch
has been issued for all areas west of the mountains Monday through
Friday. The greatest warming will begin in these areas by Monday and
Tuesday, with highs nearing 100 degrees by Tuesday for the valleys
of San Diego/Orange County into the Inland Empire. The coastal areas
will see a tougher forecast as cool westerly winds off the ocean
will have a large effect on the temperatures within a mile or so
from the coast, where some areas may stay much cooler than inland
regions. Please use this time to prepare for the incoming heat by
making sure you have enough water and products to keep cool.

The area of high pressure will continue to strengthen for the latter
half of next week. This will bring even hotter temperatures to the
area, where many of our climate sites will not only break daily
temperature records but also monthly record temperatures. Please see
the climate information section below for more details. The
temperature forecast for later next week is somewhat lower
confidence on the exact temperature details, but whatever you way
you slice it, it will be very hot for the middle of March. 850 mb
temperatures will peak near 25C during this period as the high
amplifies near 593-595 dm. Thursday and Friday look to be the
hottest days over all, with low to moderate chances of seeing highs
reach 105 degrees across the Inland Empire, as well as reaching 100
degrees and inland valleys east of the 5 and the 15 in Orange and
San Diego Counties.  The most extreme heat will be across the
Coachella Valley during this time. NBM probabilities show a
a moderate to high chance of going over 110 degrees by late next
week as well. To put this in perspective, the highest temperature
recorded in March at Palm Springs and Indio is 104 degrees (both
sites of which have a period of record over 100 years old). Low
temperatures will cool off some into the 60s for many areas below
5,000 feet with lows staying in the 70s across the lower deserts.
Please make sure to check on family, friends, and neighbors this
coming week! Outdoor activities should be limited as the duration of
this early season heat wave will lead to increased risk of heat
illness. This includes the mountains, where highs will reach into
the 80s and 90s by the latter half of the upcoming week. The ridge
looks to slowly weaken by the following weekend, which will aid in a
cooling trend.

&&

.AVIATION...
131800Z...VFR conditions with increasing high clouds through
Saturday morning. Patchy low clouds and fog over the waters and
isolated coastal areas 12-16Z Saturday. Cigs and reduced vis not
likely at coastal airports, but there is a small (20%) chance of
brief and intermittent clouds based at around 500 feet MSL and vis
3-5SM at KSAN.

&&

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

&&

.CLIMATE...

The following are the existing highest temperature records for March
for selected locations along with the highest daily NBM probability to
set a new March record for NEXT week. This is not a comprehensive list,
but the most likely locations to tie or set new monthly record high
temperatures for March are in the deserts, valleys, and mountains.


Location      March Record        NBM Probability

Palm Springs      104             100 percent (Thu,Fri)
Indio             104             100 percent (Thu, Fri)
Thermal           103             100 percent (Wed,Thu, Fri)
Ramona             94             85-95 percent (Wed, Thu, Fri)
Big Bear           80             100 percent (Thu, Fri)
Santa Ana          98             40 percent (Thu, Fri)


The existing highest 500 mb height for NKX for March is 590 DM. That
could be exceeded for multiple days next week between Tuesday and Friday.

&&

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


&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Heat Advisory until 8 PM PDT this evening for Orange County
     Coastal Areas-Orange County Inland Areas-San Bernardino and
     Riverside County Valleys-The Inland Empire-San Diego County
     Coastal Areas-San Diego County Valleys.

     Extreme Heat Watch from Monday morning through Friday evening
     for Orange County Coastal Areas-Orange County Inland Areas-
     San Bernardino and Riverside County Valleys-The Inland
     Empire-San Diego County Coastal Areas-San Diego County
     Valleys-Santa Ana Mountains and Foothills.

PZ...None.

&&

$$

PUBLIC...APR
AVIATION/MARINE...MM

NWS San Diego (SGX) Office