High Surf in California, July 4 to 7, 2018

Area Forecast Discussion
National Weather Service San Diego CA
145 PM PDT Wed Jul 4 2018

.SYNOPSIS...
High pressure will strengthen Thursday and Friday, bringing very
hot weather away from the coast Friday and Saturday. Moisture will
increase this weekend, leading to a small chance of thunderstorms,
mainly in the mountains during the afternoons through early next
week. The high pressure weakens next week and the weather will not
be as hot.

&&

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

Happy Independence Day under blue skies this afternoon.
Temperatures at 1 pm were running several degrees higher than at
this time yesterday. A trough of low pressure over the Northwest
will give way to a strong high pressure ridge over the Rocky
Mountain area Thursday and Friday. Temperatures will respond to
the compressing and warming air mass under all that subsidence,
rising a lot Thursday and much more Friday. Some inland locations
will be more than 20 degrees higher on Friday than they are be
today. Some of the eyebrow-raising forecast temperatures exceed
115 in the lower deserts and 110 for the inland valleys. Coastal
highs will have a tight gradient between the 80s expected at the
beaches, to 100+ degrees only about 10 miles inland. The marine
layer will acquiesce under all this pressure and become more
shallow Thursday and Friday. It might be all but completely non-
existent for a time on Friday with few if any low clouds by then.
Another weather feature to watch for is some increasing monsoon
moisture. With the center of the ridge north of our region, the
clockwise flow around it over Southern California will come from
the east, and bring in moisture and more unstable air from Sonora
and Arizona. We'll see mid-level altocumulus clouds and probably
some cumulus over the mountains Friday, followed by a small chance
of thunderstorms mainly in the mountains Saturday as the moisture
deepens. Some low level moisture in the lower desert will
literally dampen the ability for temperatures to rise as high on
Saturday. It will be "cooler", meaning under 115, but with the
added humidity it won't feel cooler. The easterly flow continues
next week and brings a small chance of thunderstorms mainly to the
mountains each afternoon for several days. The high pressure
weakens a bit next week and temperatures will trend downward, but
remain above average for the foreseeable future. The marine layer
will timidly rebound to bring back some coastal clouds at some
point early next week.

&&

.AVIATION...
042045Z...Coast/Valleys...Clear this afternoon. Low clouds with
bases 1500-1800 ft MSL will return to the coast after 02Z Thursday
and spread 20-25 mi inland overnight. Low clouds could reach KONT
11Z-13Z Thursday, but confidence is not high. Inland areas where low
clouds near higher terrain will have reduced VIS of 3-5 miles,
locally 1-3 miles, in fog. Low clouds expected to clear to the coast
16Z-18Z Thursday.

Mountains/Deserts...Mostly clear with unrestricted visibility
through Thursday morning.

&&

.MARINE...
No hazardous marine weather is expected through Sunday.

&&

.BEACHES...
South swells from Hurricane Fabio will create high surf and
dangerous rip currents along southwest facing beaches of Orange and
northern San Diego Counties late today through early Saturday.
Farther south, the surf will be lower and rip currents not as strong
but longshore currents will present hazardous conditions. Surf will
peak Thursday afternoon through Friday evening with sets of 7 to 9
feet, and sets of 10-12 ft at favored locations. Conditions will be
extremely hazardous for swimmers. A High Surf Advisory remains in
effect through Friday evening.

&&

.FIRE...
No high risk of explosive fire growth potential in the coming
days, but there are a few things to be aware of. 1) The coming
heat will lower humidity as temperatures rise, particularly on
Friday away from the coast. 2) A touch of offshore flow early
Friday will produce breezy conditions in foothills and pockets
below mountain passes, such as Cajon Pass. 3) The initial chance
of thunderstorms will arrive with isolated dry lightning strikes
possible late Friday. None of these features are a big enough
threat to cause alarm. Higher humidity will mitigate these factors
on Saturday.

&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Excessive Heat Watch from Friday morning through Saturday
     evening for Apple and Lucerne Valleys-Coachella Valley-
     Orange County Coastal Areas-Orange County Inland Areas-
     Riverside County Mountains-San Bernardino County Mountains-
     San Bernardino and Riverside County Valleys-The Inland
     Empire-San Diego County Coastal Areas-San Diego County
     Deserts-San Diego County Mountains-San Diego County Valleys-
     San Gorgonio Pass Near Banning-Santa Ana Mountains and
     Foothills.

     High Surf Advisory from 6 PM this evening to 9 PM PDT Friday for
     Orange County Coastal Areas-San Diego County Coastal Areas.

PZ...NONE.

&&

PUBLIC/FIRE...MM
AVIATION/MARINE/BEACHES...PG