Areal Flood Advisory 45, NWS San Diego, CA

Area Forecast Discussion
National Weather Service San Diego CA
146 PM PDT Thu Sep 9 2021

.SYNOPSIS...
Hot conditions and a moderate heat risk will continue through this
weekend. Scattered thunderstorms will occur this afternoon across
the deserts, mountains and eastern valleys. More isolated
thunderstorms will be possible on Friday. Drier conditions will
develop this weekend into next week.

&&

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

At 1 PM, thunderstorms were developing across the mountains. 20z
SPC mesoanalysis displays MLCAPE of 1000+ J/kg across the High
Deserts and mountains and 1500 J/kg across the San Diego County
Deserts. DCAPE values of 1400-1600 J/kg are common across these
areas, so strong to locally damaging winds will be possible
through this afternoon. Strong south-southeasterly winds of 30 to
40 kts are occurring at 500 mb so storms that develop across the
mountains will quickly move northwestward into the High Deserts
and eastern valleys. Modest PWAT values of 1.2 to 1.4 inches
combined with a dry subcloud layer will lower the flash flood
potential, unless a storm becomes anchored over a convergence zone
or numerous thunderstorms train over the same area. Thunderstorm
activity will continue through 01z Friday but will quickly
diminish around sunset.

Moisture will decrease slightly for Friday. Isolated thunderstorms
will again be possible through the afternoon and early evening but
will generally remain confined to the mountains and the deserts.
Much drier conditions will develop on Saturday and continue
through next week.

The ridge of high pressure centered over the Four Corners region
will slowly drift southeastward and weaken this weekend.
Persistent heat that has impacted Southern California this week
will continue this weekend. High temperatures on Friday will cool
by several degrees but will increase again for Saturday across the
mountains and inland valleys. Highs on Saturday and Sunday will
range 6 to 10 degrees above normal and a moderate to locally high
heat risk will be in place. The Heat Advisory has been extended
through Sunday evening to match this temperature trend.

Ensemble guidance begins to diverge early next week. The ECMWF Ens
shows weak longwave troughing to zonal flow, favoring cooler
temperatures while the GEFS displays a weak ridge over Southern
California. Cooling does look likely next week, but timing and
amount of cooling each day will depend on the placement of these
features. There will be significantly drier air in place by
Monday, so fire weather conditions will begin to rapidly increase
through the middle of the week. Elevated fire weather conditions
are expected especially across the mountains and desert slopes.

&&

.AVIATION...
092030Z...Coast...Mostly clear through the early evening with SCT
high clouds AOA 10K FT MSL. Patchy cigs near 1000 ft MSL possible
along the immediate coast, though TAF sites should stay mostly
clear. Patchy low clouds 500-1000 ft MSL will be patchy once again
tonight, with moderate confidence in patchy cigs mainly near
KCRQ/KSAN 10Z-16Z Friday morning.

Valleys/Mountains/Deserts...SCT-BKN clouds 20000 feet MSL today and
tonight. BKN clouds 10000-12000 feet MSL along with scattered TSRA
until around 02Z today, most likely in mountains and deserts. TSRA
bases near 9000 feet MSL with tops to 40000 feet. Gusty outflow
winds and reduced visibility possible VCTY TSRA.

&&

.MARINE...
Breezy winds near 20 kts each afternoon and evening Saturday through
Monday. No hazardous marine conditions are expected through Monday.

&&

.BEACHES...
A long-period south swell will begin to move into the coastal waters
Sunday, peaking Monday and Tuesday. This will produce elevated to
locally high surf, particularly for far northern San Diego County
and Orange County. South facing beaches will see highest surf
heights 6 to 8 feet, with surf of 3-6 feet elsewhere. Strong rip and
longshore currents are likely at all beaches.

&&

.SKYWARN...
Skywarn activation is requested.

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Heat Advisory until 9 PM PDT Sunday for Riverside County
     Mountains-San Bernardino County Mountains-San Bernardino
     and Riverside County Valleys-The Inland Empire-San Diego
     County Mountains-San Diego County Valleys-Santa Ana
     Mountains and Foothills.

PZ...NONE.
&&

PUBLIC...Schenk
AVIATION/MARINE...APR