864
FXUS66 KSGX 170426
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
926 PM PDT Mon Jun 16 2025

.SYNOPSIS...
Hot conditions will continue through Wednesday for inland locations.
Gradual cooling expected Thursday into the weekend. Patchy night and
morning low clouds and fog, that is locally dense, are expected
tonight into Tuesday along the coast. The marine layer will
gradually increase in depth Wednesday through the weekend, with low
clouds becoming more widespread and making it into the valleys.
Breezy west winds across the mountains and deserts each afternoon
and evening, strongest today.

&&

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

Update: Models are still on track with showing the ridge becoming
more amplified to our east, as the weak troughing begins to
transition out of the region over the next few days. The marine
layer is going to remain rather shallow and mostly confined to the
coastal areas, with patchy fog possible into the inland areas by
later tonight and though tomorrow morning at around 1000 ft MSL.
This should quickly scatter out by tomorrow morning shortly after
sunrise. The strong high pressure in place will result in
temperatures remaining on the warmer side through Thursday and
rather hot through Wednesday, then there will be increased
onshore flow towards the later part of the week as we begin to
become more influenced by the trough upstream, with a cooldown
going into next weekend.

(Previous discussion submitted at 132 PM):

Hot conditions will continue for inland areas through Wednesday with
widespread moderate HeatRisk in the inland valleys, mountain
foothills, and deserts. This afternoon, moderate to locally major
HeatRisk will occur in the low desert. Make sure you`re staying
hydrated and seeking shade if you`re spending time outdoors through
the middle of the week. If possible, avoid strenuous outdoor
activity during the hottest part of the day (through 5pm). Most
model guidance is showing minimal changes in high temperatures
between today and Tuesday for inland Orange County, San Diego
valleys, and mountains. For inland Orange County and western
portions of the San Diego valleys, how much marine layer low cloud
coverage develops overnight will have an impact on how hot it gets
Tuesday. Currently high resolution guidance keeps low cloud and fog
coverage quite patchy overnight, so the forecast is trending towards
the hotter end of the guidance. Patchy dense fog is possible, most
likely in San Diego county near the coastal mesas. For the Inland
Empire, temperatures will see minimal changes through Wednesday,
keeping highs between in the upper 90s to just over 100 degrees.

A very gradual cooling is expected in the deserts for Tuesday into
the weekend, although highs will remain 5 to 7 degrees above
average. The exception is the High Deserts are expected to see a
degree or two of warming on Wednesday, before continuing their
cooling trend. Widespread moderate HeatRisk will continue through
Thursday for the High Desert and Friday for the low desert.

A passing weak area of low pressure will move across central
California today, which will strengthen the onshore pressure
gradient. That will bring breezy west winds to the desert mountain
slopes, below the passes, and into the deserts during the afternoons
and evenings. Strongest winds are expected this afternoon and
evening with gusts 30 to 45 mph, locally up to 50 mph through the
San Gorgonio Pass.

Ensemble guidance is in good agreement that the ridge of high
pressure will get pushed east ahead of an incoming low pressure
system approaching the Pacific Northwest. The incoming low will
bring widespread cooling, a deeper marine layer, and increased winds
over the mountains into the deserts. Marine layer low clouds and fog
are expected to reach well into the valleys by the end of the week.
There is high confidence in dry conditions with this passing trough.
Near average temperatures will return by Friday, with below average
temperatures expected through the weekend.

&&

.AVIATION...
170330Z....Coast/Valleys...Mostly clear and VFR through the evening.
Patchy low clouds are redeveloping over the waters and will push
ashore after 04Z, but only into westernmost valleys overnight and
without uniform coverage. Bases will be around 400-600 feet MSL with
widespread vis 2-5SM, but near zero over higher coastal terrain and
western valleys. Scatter out Tuesday 15-16Z. Low clouds with similar
bases and vis will again push north and inland evening after 06Z Wed.

.Mountains/Deserts...Clear skies and unrestricted vis through
Tuesday. West winds through 08Z with gusts 20-30 kts, locally near
40 kts through the San Gorgonio Pass, leading to MOD UDDFS.

&&

.MARINE...
Wind gusts around 20 kts in the outer waters this evening near San
Clemente Island. Otherwise, no hazardous marine conditions are
expected through Saturday.

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Heat Advisory until 8 PM PDT Wednesday for Riverside County
     Mountains-San Bernardino and Riverside County Valleys-The
     Inland Empire-San Diego County Mountains-San Diego County
     Valleys.

     Heat Advisory until 8 PM PDT Tuesday for Orange County Inland
     Areas-Santa Ana Mountains and Foothills.

PZ...None.

&&

$$

PUBLIC...CO
AVIATION/MARINE...CSP