806
FXUS66 KSGX 171552
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
852 AM PDT Wed Jul 17 2024

.SYNOPSIS...
A gradual warming trend is expected into Saturday, leading to
temperatures well above average this weekend. That will mean
moderate to major heat risk for the valleys and major to extreme
heat risk for the deserts. There are slight chances of showers
and thunderstorms each afternoon in the mountains into early next
week. Coastal low clouds and fog will continue to reach into
portions of the western valleys each night and morning.

&&

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

A blob of elevated instability and altocumulus clouds produced
isolated light showers and sprinkles over the coasts and valleys
this morning. Only trace amounts were measured or reported. This
thing seems to be fading with time and moving out this morning.
Underneath this feature, the marine layer was largely undeterred,
with the routine coverage of low clouds over the coast and
westernmost valleys. However, the unstable layer floating over
the stable layer seems to be assisting the breaking up and
clearing out process. After the blob moves out, we`ll go back to
our regularly scheduled forecast of mostly sunny skies today with
cumulus buildups over the mountains leading to a slight chance of
thunderstorms this afternoon. High pressure aloft currently over
the four corners region will strengthen and migrate westward to
the Great Basin over the next few days. Temperatures inland should
climb a little each day into the weekend, gradually achieving
5-10 degrees above normal inland on Saturday. Currently we have an
Excessive Heat Watch for all deserts this weekend: Fri-Sun for
lower deserts and Sat-Sun for the high desert. Temps decrease
slightly next week, but not much. Monsoon moisture and instability
will increase slightly Thursday for a better chance of afternoon
thunderstorms in the mountains and high desert. We`ve been
advertising more monsoon action into the weekend in recent days,
but in a new, credible wrinkle of guidance, moisture decreases for
Friday through Sunday. So now we`re carrying only the slightest
of chances of thunderstorms in our highest mountains those
afternoons. Then a slight increase appears Monday and beyond. The
marine layer and coastal cloud deck will diminish under the
strengthening high pressure aloft over the next several nights and
mornings. That will help the warming trend come to the coast this
weekend, but only a couple degrees above normal. The upper high
over the Great Basin will not budge. No matter how many other
features may dampen or weaken it temporarily, it is resilient, so
keep planning for hotter than normal summer weather inland.

&&

.AVIATION...
171500Z...Coast/Valleys...Areas of low clouds within 20 miles of the
coast with bases 1000-1400 ft MSL and tops to 2400 ft MSL will clear
through 18Z except local stratus remaining along the beaches through
this afternoon. Most VIS will be 6+ miles today. Low clouds will
develop within 10 miles of the coast 02Z-06Z Thu and spread up to 20
miles inland by 12Z Thu with bases 900-1300 ft MSL and tops to 2000
ft MSL and local VIS 3-5 miles in the coastal valleys 08Z-17Z Thu.
Similar clearing times are likely Thu morning. Otherwise, SCT-BKN
clouds at/above 10000 ft MSL will decrease through 19Z today.

Mountains/Deserts...Isolated SHRA/TSRA will occur 20Z today-02Z Thu.
CB bases will be 10000-12000 ft MSL with tops to 3500 ft MSL.
Gusty outflow winds and reduced vis in RA VCTY TSRA.

&&

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

&&

.BEACHES...
Long period 3 foot SSW swell (200-210 degrees) will bring elevated
surf of 4-6 feet with sets up to 7 feet for south-southwest facing
beaches in both Orange and San Diego counties and a high risk of rip
currents at all beaches. A Beach Hazard Statement remains in effect
through Thursday evening. Swell and surf will lower Friday, but the
rip current risk will remain high.

&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Beach Hazards Statement through Thursday evening for Orange
     County Coastal Areas-San Diego County Coastal Areas.

     Excessive Heat Watch from Saturday morning through Sunday
     evening for Apple and Lucerne Valleys.

     Excessive Heat Watch from Friday morning through Sunday evening
     for Coachella Valley-San Diego County Deserts-San Gorgonio
     Pass Near Banning.

PZ...None.

&&

$$

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