Severe Thunderstorm Warning 11, NWS San Diego, CA

Area Forecast Discussion
National Weather Service San Diego CA
131 PM PDT Sat Sep 3 2022

.SYNOPSIS...
Strong upper level high pressure centered over the Great Basin
will continue the heat wave into next week, except at the highest
elevations in the mountains. The hottest days for coastal areas are
expected this weekend. Isolated thunderstorms may develop near the
mountains and drift westward into the valleys and coastal areas
through Sunday. The high will weaken after mid next week. Slow
cooling will spread inland then, and there is a potential for some
rain by the weekend.

&&

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

It is a hot one today to be sure, even to the coast, where
temperatures at midday were running well into the 90s. If the heat
weren't enough, there is a threat for thunderstorms as well. They
should be isolated, but they may produce some strong microburst
winds and dangerous lightning strikes, besides brief, very heavy
rainfall. As of 1 PM, cumulus clouds were developing just off the
mountain crests and spreading rapidly westward.

Satellite imagery shows the cloud and mid-level moisture shield
around Javier, edging slowly northward. This could move over
southern San Diego County overnight, and could bring a few showers.
As warm as last night was, tonight may be even warmer west of the
mountains, elevating the heat risk all the way to the coast. There
is also a chance for some evening convection near our southern
deserts. The headline for the near term is the warm night ahead,
especially for San Diego County and continued hot weather through the
Labor Day weekend.

Strong high pressure aloft will remain anchored over the Great Basin
through the first half of next week with a n E-W oriented ridge axis
from off the Central Coast of CA, to the High Plains. Easterly flow
is accelerating around the southern flank of the high as Tropical
Storm Javier squeezes the pressure gradient over SoCal. There is
some subtropical moisture embedded in this flow, which could pop a
few isolated thunderstorms across the region, especially over and
west of the mountains this weekend. Some drying is indicated after
Monday, which should decrease the thunderstorm threat, but could add
to the already excessive heat. The Excessive Heat Warning remains in
effect through at least Tuesday, and looks like it may need to be
extended through at least Wednesday for those areas not already
covered.

We can say with a moderate degree of confidence, that the excessive
heat will end after Thursday of next week as all of the ensemble
members of the GFS/ECMWF/CMC show it happening. In the meantime, we
may have some fluctuations over coastal areas as the onshore flow
attempts to build a shallow marine layer inland at times. This is
reflected in various cluster solutions showing a wider spread in
maximum temperatures at coastal sites.

Another forecast parameter showing a wide spread in solutions is
precipitation for late next week. The controls for these models all
show the high over the Great Basin weakening enough to allow the
next Tropical Storm to move farther north along the west coast of
Mexico, possibly affecting SoCal. This will take some time to sort
out, but for now we have some POPS late in the forecast period.

&&

.AVIATION...
031910Z...FEW-SCT clouds at/above 10000 ft MSL will continue through
today, with mostly unrestricted VIS.  There is a slight chance of
TSRA through this evening, with CB bases 10000 ft MSL and tops to
40000 ft MSL. LocalLY gusty east winds over 25 knots will be
possible through 13Z in the deserts which could create local VIS
below 3 miles in BLDU. Low confidence in any direct TSRA impacts to
any of the TAF sites through this evening.

&&

.MARINE...
No hazardous marine weather expected through Wednesday.

&&

.BEACHES...
A pair of south swells will bring elevated surf and a high risk of
rip currents through the holiday weekend. The first swell of 2-3
ft/14-15 sec from 190 degrees peaks today, generating surf of 3-5 ft
on south facing beaches. A second swell from 170 degrees of 3-4
ft/10-12 sec generated from the newly developed Tropical Storm
Javier is forecast to arrive on Sunday and continue Monday,
maintaining surf of 3-5 ft on south facing beaches, with potential
for sets to 6 ft for Tuesday and Wednesday mainly on south-facing
beaches in Orange County.

&&

.FIRE WEATHER...
Temperatures will remain well above average through the first half
of next week. Moisture levels will be elevated through Monday, then
decrease into the middle of next week. The marine layer has
dissipated today, but should return early next week, helping to cool
coastal areas a bit more. The heat inland will raise mixing heights
and increase the potential for large vertical plume growth with any
new fires that develop.

Isolated thunderstorms are expected today. Any that develop will
move rapidly westward across the coastal basin. The main threat is
for dry lightning strikes, and gusty outflow winds. There will be a
threat of locally heavy rainfall if one of them anchors along the
coastal facing slopes of the mountains, also where new cell
development repeats over the same area, but in general, any wetting
rainfall is expected to remain isolated.

&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Excessive Heat Warning until 8 PM PDT Tuesday for 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.

     Excessive Heat Warning until 8 PM PDT Wednesday for Apple and
     Lucerne Valleys.

PZ...None.

&&

PUBLIC...10
AVIATION/MARINE/BEACHES...Adams

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SAN DIEGO CA
936 AM PDT SAT SEP 3 2022

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0330 PM     TSTM WND GST     3 WSW PALOMAR MOUNTAIN  33.30N 116.91W
09/02/2022  M47 MPH          SAN DIEGO          CA   MESONET

            THUNDERSTORM DEVELOPING OFF OF PALOMAR
            MOUNTAIN PRODUCED 47 MPH GUST AT CUCA RANCH.

&&

10