Flash Flood Warning 3, NWS San Diego, CA

359 
WGUS76 KSGX 160042
FFSSGX

Flash Flood Statement
National Weather Service San Diego CA
542 PM PDT Tue Aug 15 2023

CAC073-160052-
/O.CAN.KSGX.FF.W.0003.000000T0000Z-230816T0115Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
San Diego CA-
542 PM PDT Tue Aug 15 2023

...FLASH FLOOD WARNING IS CANCELLED FOR EAST CENTRAL SAN DIEGO 
COUNTY...

The heavy rain has ended. Flooding is no longer expected to pose a 
threat. Please continue to heed any remaining road closures.

LAT...LON 3317 11673 3306 11667 3301 11655 3301 11632
      3316 11631 3327 11674

$$

MM

Area Forecast Discussion
National Weather Service San Diego CA
140 PM PDT Tue Aug 15 2023

.SYNOPSIS...
Inland warming continues through today and Wednesday as high
pressure expands westward. Mid level moisture in southeast flow
aloft will bring a slight chance of light showers during the nights
and mornings through Wednesday and a slight chance for afternoon
showers and thunderstorms, mainly for the mountains and deserts.
A low pressure system will move near the central California coast
on Thursday and Friday, ushering in cooler air, but also drier
air aloft which will mitigate the thunderstorm threats on Thursday
and Friday afternoons. The low pressure system also may draw in
more tropical and/or monsoonal moisture, increasing cloud cover and
humidity as well as chances for widespread rainfall later this
weekend.

&&

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

High pressure over the southwestern US will expand westward over
the next several days, ushering in a warming trend. Highs across
Southern California over the next several days will top out
generally 4 to 8 degrees warmer than seasonal averages, with
Excessive Heat Warnings in effect for the lower desert regions,
and Heat Advisories in effect for the mountains of Riverside and
San Diego Counties as well as the Inland Empire. The one
mitigating factor to any heat concerns over the 24 to 36 hours
stems from the potential for nocturnal and morning convection in
the mountains and deserts. Lingering cloud cover and shower
activity could potentially lead to a reduction in daytime highs.
There still remains at least slight chances for thunderstorms this
afternoon due to some elevated instability. Wednesday afternoon,
per hi-res-guidance, looks to be the more active day at the
moment.

By Thursday and Friday, upper level low pressure will begin
strengthen over the central CA coast, bringing in a gradual
cooling trend as well as drier southwest flow aloft. Hot daytime
temperatures are still expected Thursday afternoon but a more
notable cooling trend will set in on Friday. Due to the drier
southwest flow, thunderstorms look less likely to occur on
Thursday and Friday as well.

The other impact from low pressure off the central CA coast will
be how it interacts with a developing tropical system off the
southwest coast of Mexico. Impacts to Southern California are
still largely dependent on the size, intensity, and track of this
eventual system. The latest update from the National Hurricane
Center has an 80% chance for development within the next 48 hours,
and a 90% chance in the next 7 days.

Confidence in additional moisture and cloud cover later this
weekend is increasing. EPS PWAT guidance suggest PWAT increases
into the 1.5-2.5 inches across much of Southern California, with
the highest values occurring generally east of the mountains.
Chances for measurable precipitation also are higher in these
regions, though roughly 1/4 to 1/3 of EPS members have measurable
rainfall occurring in/near San Diego on Sunday. Early projections
for any sort of rainfall Saturday through Monday look to be
between 0.50-1.00 inch west of the mountains, with potential for
several inches in and east of the mountains. These amounts are
very much subject to change as we refine details regarding this
eventual tropical system.

Another feature of note will be the potential push of
easterly/offshore flow that occurs this weekend as the system
approaches. This would not only affect rainfall amounts but also
potentially lead to notably warmer temperatures, reflected
especially in overnight lows as downsloping winds continue. Will
opt to keep overnight lows this weekend a few degrees warmer than
NBM guidance for now.

&&

.AVIATION...
151945Z...Coast...Areas of low clouds are lingering at beaches,
particularly in San Diego County this afternoon. Patchy stratus with
bases 400-800 ft MSL, locally down to 200 ft MSL, spreading inland
around 05Z Wed. Low cloud coverage is expected to reach 10-15 mi
inland overnight, with the greatest coverage in San Diego County.
Vis reductions of 2-4SM in BR/HZ expected. Low clouds expected to
scatter out and vis restrictions expected to clear 17-19Z Wed.

Valleys...FEW-SCT clouds at/above 15,000 ft MSL and 5 to 15 percent
chance of -SHRA near KONT and KSBD, respectively, through 00Z Wed.
VCSH possible for KONT/KSBD overnight(10 to 15 percent chance).

Mountains/Deserts...Scattered SHRA/TSRA over the mtns and locally
into the deserts through 02Z Tue with CB bases at 10,000 feet MSL
and tops to 20,000 feet MSL. Iso -SHRA possible overnight (15-20
percent chance).

&&

.MARINE...
Northwest wind gusts around 20 kt over the outer waters each
afternoon through Thursday. Gusty northwest winds may create rough
conditions near the entrance of the San Diego Bay.

&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Heat Advisory until 8 PM PDT Thursday for Riverside County
     Mountains-San Bernardino and Riverside County Valleys-The
     Inland Empire-San Diego County Mountains.

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

PZ...None.

&&

PUBLIC...Adams
AVIATION/MARINE...CO

Special Weather Statement
National Weather Service San Diego CA
407 PM PDT Tue Aug 15 2023

CAZ050-058-062-160000-
San Diego County Mountains CA-San Diego County Deserts CA-
San Diego County Inland Valleys CA-
407 PM PDT Tue Aug 15 2023

...A strong thunderstorm will impact portions of central San Diego
County through 500 PM PDT...

At 406 PM PDT, Doppler radar was tracking a strong thunderstorm over
Hwy 78 Between Banner And S2, moving northeast at 55 mph.

HAZARD...Winds in excess of 40 mph.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects.

Locations impacted include...
Hwy 78 Between Banner And S2, Julian, Hwy 78 Between S2 And Borrego
Springs Rd, Hwy 79 Between Julian And Lake Cuyamaca, Lake Cuyamaca,
Hwy S2 Between Hwy 79 And Hwy 78, Hwy 78 Between Ramona And Santa
Ysabel, Banner, Wynola, Shelter Valley, Santa Ysabel, and Santa
Ysabel Indian Reservation.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

Torrential rainfall is also occurring with this storm and may lead to
localized flooding. Do not drive your vehicle through flooded
roadways.

Frequent cloud to ground lightning is occurring with this storm.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

&&

LAT...LON 3299 11662 3311 11670 3319 11646 3304 11645
TIME...MOT...LOC 2306Z 239DEG 49KT 3313 11649

MAX HAIL SIZE...0.00 IN
MAX WIND GUST...40 MPH