FXUS66 KSGX 192040
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
140 PM PDT Fri Jul 19 2024

.SYNOPSIS...
High pressure over the Southwest will bring a very hot weekend
inland, along with very warm nights. Moderate to major heat risk
is expected in the valleys and mountains with major to extreme
heat risk for the deserts. A return of greater monsoonal moisture
will bring more humid conditions for Monday through Thursday,
along with a chance for mainly afternoon showers and
thunderstorms in the mountains and deserts. Coastal low clouds
will continue to develop at times during nights and mornings.

&&

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

Low clouds have clung to the coast into this afternoon, probably
a result of the strengthening marine inversion. That warming air
mass above a shallower marine layer bringing on the inland heat,
has strengthened that inversion. Temperatures at most stations
away from the coast are running a few degrees higher than
yesterday at 1 pm, confirming that our heat wave is underway. The
strengthening high pressure aloft will continue to squash the
marine layer, causing clouds and fog to back off in spatial and
temporal coverage overall and becoming patchier. But the really
strong marine inversion will make full clearing at the beaches
dubious or at least questionable each afternoon. Inland heat is
the main focus for the next several days. Inland heat risk will be
high to extreme through at least Sunday. The high overnight
temperatures are probably more responsible than the high afternoon
temperatures for creating that high heat risk. The high pressure
aloft weakens very slightly Sunday and Monday, so temperatures
will come down a couple degrees. But the high pressure appears to
strengthen again Tuesday and Wednesday and dew points come up to
keep those nights extra warm. So not much cooling is happening
early next week. Monsoon moisture is already decreasing today as
evidenced by the few cumulus clouds over the highest mountains not
growing into thunderstorms. It will remain dry through at least
Sunday. The moisture begins to increase again Monday for marginal
chances of thunderstorms Monday afternoon in the mountains,
followed by more moisture and instability Tuesday and Wednesday
afternoons for a higher chance across mountains and deserts. The
moisture appears to retreat again Thursday and Friday for
decreasing chances. The consensus of most guidance for late next
week is to break down the high pressure ridge with an amplifying
trough on the West Coast. Guidance differs on how strong the upper
ridge will be next week, and the relative timing on its
breakdown. We expect a cooling trend toward next weekend, but how
much cooling is uncertain.

&&

.AVIATION...
192030Z...Coast/Valleys...Areas of BKN clouds will continue
this afternoon at the beaches with bases of 1000 ft MSL and local
VIS 2-4 miles in HZ. VFR conditions will elsewhere through 00Z Sat.
Stratus will gradually develop this evening with TEMPO BKN
conditions within 5 miles of the coast 00Z-06Z Sat, then stratus
spreading up to 15 miles inland 06Z-12Z Sat with bases 600-1000 ft
MSL and tops to 1200 ft MSL and local VIS 1-3 miles over higher
coastal terrain 08Z-16Z Sat. Most areas will clear 15Z-17Z Sat,
though some stratus could linger again along the coast Sat afternoon.

Mountains/Deserts...There is now only a 5-10 percent chance of TSRA
over the mountains and adjacent deserts through 02Z Sat. Otherwise,
SCT-local BKN clouds with bases around 10000 ft MSL will occur over
the mountains through 02Z Sat with mostly clear skies this evening
through Sat and unrestricted VIS.

&&

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

&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Heat Advisory until 9 PM PDT Sunday for Riverside County
     Mountains-San Bernardino County Mountains-San Bernardino
     and Riverside County Valleys-The Inland Empire-San Diego
     County Mountains-San Diego County Valleys.

     Excessive Heat Warning from 11 AM Saturday to 9 PM PDT Sunday
     for Apple and Lucerne Valleys.

     Excessive Heat Warning until 9 PM PDT Sunday for Coachella
     Valley-San Diego County Deserts-San Gorgonio Pass Near
     Banning.

PZ...None.

&&

$$

PUBLIC...MM
AVIATION/MARINE...Maxwell