815
FXUS66 KSGX 211628
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
928 AM PDT Fri Jun 21 2024

.SYNOPSIS...
Hot conditions expected through the weekend and into next week
for the valleys, mountains, and deserts. A surge of monsoonal
moisture will bring higher humidity and a slight chance for
showers and thunderstorms on Sunday. A shallow marine layer will
keep coastal highs in the 70s and 80s.

&&

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

A ridge of high pressure currently over Texas, will drift west
towards the Southwest United States this weekend. That ridge of high
pressure will remain over the Four Corners region through most of
next week. The ridge will result in hot conditions across Southern
California and allow for an increase in monsoonal moisture Sunday,
potentially into Monday. Today will be 3 to 5 degrees hotter than
yesterday for coastal areas; 5 to 10 degrees hotter than yesterday
for the valleys and deserts; in the mountains highs will be 10 to 15
degrees hotter than yesterday. Conditions will continue to warm into
Saturday with widespread moderate to major heat risk away from the
coast. Temperatures will get knocked down a few degrees on Sunday
for inland areas due to an increase in moisture. Even with
temperature readings a few degrees lower than Saturday, hot and
muggy conditions are expected.

Temperatures for locations in and west of the mountains will peak
on Saturday, gradually decreasing into next week. Widespread
moderate heat risk will continue into Sunday in and west of the
mountains, with heat risk becoming locally moderate for the
eastern portions of the valleys by Monday. High temperatures in
the deserts will fall a few degrees on Sunday, before increasing
again for Monday. Conditions in the deserts will remain hot enough
for moderate to major heat risk through Thursday. For the end of
next week, a trough of low pressure will approach the Pacific
Northwest, weakening the ridge and pushing it off to the south and
east. This will allow temperatures to fall to within a few
degrees of the seasonal normals.

For Sunday, a surge of mid-level monsoonal moisture will bring
higher humidity to the area. The increased humidity will make it
harder to keep cool during outdoor activities even with high
temperatures a few degrees cooler than Saturday. Model guidance
continues to show an easterly wave in the southeast flow around the
Four Corners making it`s way across Southern California Sunday. This
shortwave interacting with the monsoonal moisture will destabilize
the atmosphere sufficiently for possible showers and thunderstorms
Sunday. Guidance is also showing an increase of Most Unstable CAPE
in the mid-levels of the atmosphere over the coastal waters and near
the coast, increasing the chance for elevated convection. Measurable
precipitation (25-30%) and thunderstorms (15-20%) are most likely
over the mountains, with lesser chances of measurable
precipitation (15-20%)and thunderstorms (5-10%) elsewhere.

&&

.AVIATION...
211525Z...Coast/Valleys...Low cloud bases 1100-1300 ft MSL with tops
to 1700 ft MSL and local VIS 3-5 miles in BR over higher coastal
terrain and western portions of the valleys.

CIG impacts likely at KSAN, KCRQ and KSNA to 16Z. Clearing to the
coast will occur 15Z-18Z. Confidence in clearing time at KSAN of
around 16Z is moderate to high.

Low cloud with bases 1100-1300 ft MSL with tops to 1700 ft MSL moving
in after about 22/03Z with local VIS 3-5 miles in BR over higher
coastal terrain and western portions of the valleys after 22/03Z.
Cloud coverage becoming more erratic Sat morning. CIG and/or VIS
impacts not expected at KONT or KSBD.

Mountains/Deserts...Mostly clear with unrestricted VIS through Fri
evening. West winds with gusts 20-35 kt through San Gorgonio Pass
and other favored locations on the desert slopes and into the
deserts will continue to weaken through late Friday.

&&

.MARINE...
A system moving by to the south will bring a small chance (less than
20%) of precipitation and a 10% or less chance of lightning Saturday
night through Sunday. Otherwise, no hazardous marine conditions are
expected through next Wednesday. See the Marine Weather Statement
for more information on the potential for thunderstorms.

&&

.BEACHES...
There is a slight chance of a thunderstorm Saturday night through
Sunday which could produce cloud-to-ground/cloud-to-water lightning
strikes. Chances of a lightning strike near any particular beach are
currently 10 percent or less Saturday night and Sunday.

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Heat Advisory from 10 AM Saturday to 8 PM PDT Sunday for Orange
     County Inland Areas-San Bernardino and Riverside County
     Valleys-The Inland Empire.

     Heat Advisory from 10 AM to 8 PM PDT Saturday for Riverside
     County Mountains-San Bernardino County Mountains-San Diego
     County Mountains-San Diego County Valleys.

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

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

PZ...None.

&&

$$

PUBLIC...CO
AVIATION/MARINE/BEACHES...Small