Severe Thunderstorm Warning 5, NWS San Diego, CA

Area Forecast Discussion
National Weather Service San Diego CA
214 PM PDT Sat May 20 2023

.SYNOPSIS...
Persistent low clouds will occur each night and morning across
the coast and valleys through next week, with minimal clearing for
the coast each day. Thunderstorms will be possible over the
mountains and deserts each afternoon through Monday, with the most
widespread activity occurring today. Longwave troughing returns
early next week, with cooling, a deepening marine layer and drier
conditions expected.

&&

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

Scattered thunderstorms are anticipated mainly over the San
Bernardino Mountains and High Desert area from late this afternoon
through middle evening. Activity over far Northeastern San
Bernardino continues to progress southwest towards the San
Bernardino Mountains this afternoon and we anticipate outflow from
that cluster of thunderstorms to reignite convection late this
afternoon along the upslope north portion of the mountains
including the Big Bear area.

Daytime heating will contribute to moderately conducive
conditions for updrafts but again easterly wind shear will be
difficult to combat at least with the initial convection. Thus the
best chance of showers and thunderstorms will be late afternoon
through mid- evening across the mountains. The latest HRRR is
targeting the San Bernardino Mountains and the High Desert for the
best chances, as well, and that makes sense given the better
heating and less debris cloud cover.

Good storm movement should limit torrential downpours although
some training is possible due to the persistent storm motion.
Instability is also maximized over San Bernardino County this
afternoon, with lesser indices over the Riverside Mountains, and
especially in San Diego County which was limited earlier today by
debris cloudiness from nocturnal convection ended earlier this
morning. The debris clouds could limit instability over the San
Diego County Mountains but could help to scour out some of the low
clouds near the coast as previous mornings.

Convection will die off by late this evening, certainly most
activity before midnight, with the late convection today should
preclude nocturnal convection tonight until perhaps very late in
the evening.

For Sunday afternoon and evening, remnant boundaries, diurnal
heating and persistent mid-level moisture will contribute to
another round of scattered showers and thunderstorms once again.
The chances for convection on Sunday will be very similar to
today, most likely.

Long Term Discussion:

Lesser chances for convection on Monday due to declining
instability and mid level moisture advection, with the pattern
finally shifting to a drier westerly flow for Tuesday onward. A
baggy trough will settle over SoCal for mid to late next week,
bringing a healthy onshore flow each day, but otherwise benign
weather and slightly cooler conditions for inland areas, should be
expected through the end of next week, with good continuity in
the ensemble and deterministic forecasts.

&&

.AVIATION...
202030Z...Coast/Valleys...Areas of BKN/OVC low clouds will continue
this afternoon within 5-10 miles of coast with bases 1300-1700 ft
MSL with tops to 2200 ft MSL. BKN/OVC low clouds with similar
bases/tops will spread to 10-15 miles inland 00Z-04Z Sun and
eventually through most valleys by 10Z Sun, with higher terrain
obscured at times and local VIS below 1 mile in BR/FG in the
valleys. Clearing will occur 16Z-19Z Sun except for areas of stratus
lingering within 5 miles of the coast Sun afternoon.

Mountains/Deserts...ISO-SCT TSRA will occur through 04Z Sun over the
mountains and deserts, with greatest coverage in San Bernardino
County. CB bases will be 9000-10000 ft MSL and tops to 35000 ft MSL.
Otherwise, SCT-BKN clouds at/above 10000 ft MSL will prevail with
mostly unrestricted VIS. There is a chance of TSRA in the mountains
and deserts again Sun afternoon.

&&

.MARINE...
No hazardous marine conditions are forecast through Thursday.

&&

.BEACHES...
The long-period southerly swell will continue to dissipate this
afternoon, with most surf below 6 feet. The rip current risk will
remain high this afternoon but then decrease Sunday.

&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...None.

&&

PUBLIC...Brotherton
AVIATION/MARINE/BEACHES...Maxwell