399
FXUS66 KSGX 220355
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
855 PM PDT Fri Jun 21 2024

.SYNOPSIS...
Hot conditions expected through the weekend for the valleys,
mountains, and deserts and in the deserts next week. A surge of mid-
level moisture will bring higher humidity and a slight chance for
showers and thunderstorms from the coast to the deserts late
Saturday night into Sunday, locally in the San Bernardino mountains
on Monday afternoon. 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...

.Evening Update...
Warmer weather occurred inland today compared to yesterday. Highs
reached into the low to mid 90s across the Inland Empire and over
110 degrees in the lower deserts, while beautiful beach weather
was had with highs in the 70s. GOES imagery shows low clouds
slowly reforming near the San Diego Co coastline this evening.
The marine layer will be slightly shallower tonight than this
morning, keeping low clouds within around 15 miles of the beaches.
Probabilities for temperatures over 100 degrees are highest
tomorrow across the eastern and southern portions of the Inland
Empire and much of the high desert, with guaranteed highs at or
above 110 degrees again across the lower deserts.

Please be mindful if venturing outdoors for recreation this
weekend as most areas will be quite warm. Even in the mountains,
highs will be in the upper 80s to mid 90s from Julian to
Idyllwild. Remember to take frequent breaks and drink plenty of
fluids if outdoors.

Latest hi-res guidance shows minimal activity for the region
Saturday. Moisture will increase by Saturday night into Sunday.
A small chance for storms exists in most areas our coverage area
with the HRRR showing the greatest chance for storms along the
mountain spine into some adjacent valleys west of the mountains.
Forecast looks reasonable for now, but we will continue to assess
as the event gets closer.


.Previous Discussion (216 PM Friday)...

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 mid-level moisture Sunday,
with some moisture lingering into Monday. Widespread moderate to
major heat risk away from the coast is expected on Saturday.
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 with highs 5 to 10 degrees above average.

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 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 its way
across Southern California Sunday. This shortwave interacting
with the mid-level moisture will destabilize the atmosphere
sufficiently for showers and thunderstorms Saturday night and
Sunday from the coast to the deserts. The increase in Most
Unstable CAPE in the mid-levels of the atmosphere over the
coastal waters and near the coast is indicating the potential for
elevated convection which could bring thunder and lightning with
little to no rainfall accumulation. Measurable precipitation
(25-35%) and thunderstorms (15-20%) are most likely over the
mountains, with lesser chances of measurable precipitation
(15-20%)and thunderstorms (5-10%) for the coast, valleys, and
deserts. Isolated thunderstorm chances will linger Monday
afternoon in the San Bernardino Mountains (20%).

&&

.AVIATION...
220345Z...Coast/Valleys...Satellite depicts slow and patching return
of marine clouds. This is expected to continue patchy tonight and
late. A shallower marine layer brings the threat for MVFR in fog
and IFR ceilings at CRQ and 30 percent chance of ceiling below
1000 FT AGL at SAN for 10 to 14z. Early burn off between 15 and 16Z
on Saturday.

Mountains/Deserts...
Clear and lighter winds than recently. Light diurnal winds on Saturday
but very hot again. Late after winds of 20 kt in the passes.

&&

.MARINE...Tropical moisture is expected to arrive Saturday night
through Sunday morning. Meanwhile patchy low clouds. The moisture
is enough with a weak disturbance to bring a threat for widely
scattered lightning and brief showers Saturday night and Sunday morning.
Marine weather statement continues for this weather.

&&

.BEACHES...
There is a slight chance of a thunderstorm Saturday night through
Sunday morning which could produce cloud-to-ground/cloud-to-water lightning
strikes. Chances of a lightning strike near any particular beach are
currently 10-20 percent or less Saturday night and Sunday. Rain showers will
generally be light to moderate and brief.

&&

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


&&

.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-San Diego County Valleys.

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

     Excessive Heat Warning from 10 AM Saturday to 8 PM PDT Thursday
     for Apple and Lucerne Valleys-Coachella Valley-San Diego
     County Deserts-San Gorgonio Pass Near Banning.

PZ...None.

&&

$$

PUBLIC...APR/CO
AVIATION/MARINE...Tardy