Flash Flooding and Flooding in California, July 30 to 31, 2022

Area Forecast Discussion
National Weather Service San Diego CA
838 AM PDT Sat Jul 30 2022

.SYNOPSIS...
Monsoonal moisture and instability will support scattered showers
and thunderstorms this weekend. The storms will be focused in the
mountains and deserts in the afternoons, but a few could drift
farther west into the valleys. Conditions become less favorable
for widespread showers and thunderstorms on Monday, then decrease as
drier and more stable conditions return. Temperatures will be near,
to slightly below average through next week.

&&

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

Mid and high-level clouds were widespread over the Desert SW this
morning, and we still had a fair amount of marine clouds over the
coastal waters, some of which were along our coaSt earlier this
morning. Our 12Z Miramar sounding had an 8C inversion based near
1400 FT MSL and boasted a very wet 1.9 inches of precipitable water
throughout the column. Much of this was above 10K FT, where parts of
the column were nearly saturated. Winds aloft were weaker than
yesterday, but mostly E-NE at 10-15KT. Most unstable Cape was 395
J/K. No forecast updates are planned this morning.

Due to the very high moisture level in the atmosphere, and a weak
easterly wave traversing the area, a Flood Watch has been issued
today for areas away from the coast. Should convection get going to
any degree, very heavy rainfall rates are possible, which could lead
to flash flooding. Factors limiting strong afternoon convective
development today include some weak subsidence, behind the axis of
the wave, and an abundance of mid/high clouds, which could limit
afternoon heating. A slow drying of the atmosphere begins on Sunday
and will continue through Tuesday, but sufficient moisture and
instability continue to support PM thunderstorms, gradually becoming
more tethered to the mountains and high desert areas as winds aloft
turn more southerly.

High pressure aloft, centered over Lake Tahoe this morning, will
slowly drift east, and then SE through Monday and eventually merge
with an E-W oriented ridge along the Gulf Coast States next week.
Between these two systems, a conveyor belt has been set up,
transporting moisture into the Desert SW from the Gulf of Mexico.
This will continue through Monday, before flow aloft turns more SW
over California, in conjunction with a trough just off the West
Coast. That should end this monsoonal episode until perhaps next
weekend, when flow aloft again turns SE and guides more moisture
our way.

Given the potential for a lot of clouds over the next few days,
followed by weakening high pressure aloft later next week, daytime
temperatures are forecast to be near or below average through the
forecast period.

&&

.AVIATION...
301500Z...Coast/Valleys...Patchy low clouds will continue to clear
coastal areas through 17Z. Otherwise, SCT-BKN high clouds at/above
10,000 feet MSL will prevail through this afternoon. TSRA possible
18Z today through 05Z Sunday, most likely in the eastern valleys.
Lightning, gusty erratic winds and locally heavy rain are possible
in any storm that develops. Low clouds will return to coastal areas
after 05Z Sunday, with bases 1200-1500 feet MSL.

Mountains/Deserts...SCT-BKN high clouds at/above 10,000 feet MSL
through today. TSRA expected 18Z today through 05Z Sunday.
Lightning, gusty erratic winds and heavy rain are possible in any
storm that develops.

&&

.MARINE...
A slight chance of thunderstorms will develop this afternoon, with
thunderstorms possible through Sunday afternoon. Cloud-to-water
lightning and hazardous winds and seas will be possible near any
thunderstorms. An increasing southerly swell from 180-200 degrees
with a period of 12-14 seconds is expected Sunday through Wednesday
due to the remnants of Hurricane Frank.

&&

.BEACHES...
There is a slight chance of thunderstorms today through Sunday at
the beaches. Any thunderstorm could generate deadly lightning.

Hurricane Frank will generate hazardous surf conditions, including
strong rip currents, Sunday night through Wednesday. The 6 foot
south swell from 180-200 degrees at a period of 12-14 seconds will
generate surf of 4-6 feet with local sets to 7 feet, mainly at south-
facing beaches. Highest surf will be in northern Orange County.

&&

.SKYWARN...
Skywarn activation may be requested today.

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Flood Watch from 11 AM to 11 PM today for the
     Apple and Lucerne Valleys-Coachella Valley-Riverside County
     Mountains-San Bernardino County Mountains-San Bernardino
     and Riverside County Valleys-The Inland Empire-San Diego
     County Deserts-San Diego County Mountains-San Gorgonio Pass
     Near Banning.

     Beach Hazards Statement from 8 AM today through
     Wednesday afternoon for Orange County Coastal Areas-San
     Diego County Coastal Areas.

PZ...NONE.

&&

PUBLIC...10
AVIATION/MARINE/BEACHES...Connolly