Flash Flood Warning 2, NWS Los Angeles, CA

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
217 PM PDT Sun Sep 11 2022

.SYNOPSIS...11/216 PM.

A warm, humid, and unsettled weather pattern will continue through
Monday, then slowly give way to a more typical cool marine layer
pattern starting Tuesday and continue into next weekend, with
night and morning low clouds and fog along the coast and into some
of the valleys. Temperatures will turn several degrees below
normal across the region by mid-week.

&&

.SHORT TERM (TDY-WED)...11/214 PM.

Partly cloudy skies overall covered the forecast area early this
afternoon. However, scattered showers and thunderstorms have
already developed over the mtns due to the continuation of a
warm, humid and unstable airmass as the remnants of tropical
system Kay continue to affect the area. The latest NAM showed
very high PWAT values along the coast this morning (up to 2
inches). PWAT values are forecast to lower this afternoon over
L.A./VTU Counties to 1.00-1.25 inches or so which is still quite
high. Surface LI's were forecast to peak around 4.5 this afternoon
over the mtns, with MUCAPE values up to 1300 J/kg and K-indices
peaking near 42 deg C.

All the ingredients are in place for additional showers and
thunderstorms to develop over the area this afternoon into this
evening, especially in the mtns and interior SLO/SBA Counties. The
steering flow is expected to be around 10-15 mph out of the E or
SE and any thunderstorms that develop could train over the same
areas. With the high amount of available moisture and relatively
weak steering flow, any thunderstorms would be capable of
producing very heavy rain (hourly rainfall rates of 1-2 inches)
which could lead to flash flooding, even outside recently burned
areas. A a result, a Flash Flood Watch is in effect thru this
evening for all the interior mtns and the interior vlys of SLO/SBA
Counties. Even outside these areas, some heavy rain will still be
possible in any thunderstorms. Additionally, any thunderstorms
that develop this afternoon into this evening will also be capable
of producing strong, gusty winds, small hail, and dangerous
cloud-to-ground lightning.

The upper level low associated with the remnants of Kay was a
couple of hundred miles off of the nrn Baja coast early this
afternoon. This system will slowly move NE and weaken into an
open trof over srn CA tonight into Mon, then finally move off to
the E Mon night. A broad zonal flow aloft will develop over srn CA
for Tue, with H5 heights around 580-582 dam. A weak upper level
trof over the E Pac Tue night will move into the CA coast on Wed,
with H5 heights lowering to about 579-582 dam from N-S across the
forecast area.

Skies will be partly to mostly cloudy overall across the area
tonight thru early Mon evening. There will continue to be enough
moisture and instability over the region for a chance of showers
and slight chance of thunderstorms over much of the region Monday
afternoon, and over much of L.A./VTU Counties Mon evening. The
best chance of thunderstorms on Mon will be over the mtns. The
steering flow is forecast to be even weaker than today, and PWAT
values will remain high at 1.00-1.50 inch. Any thunderstorms Mon
would be slow-moving and could produce heavy rain. The threat of
flash flooding may continue for the interior mtns and vlys,
possibly into the Antelope Vly, and this situation will be closely
monitored for potential Flash Flood Watch extensions.

By late Mon night, marine layer clouds are expected to develop
over the coast and adjacent vlys and continue into Tue morning.
Skies are then expected to become mostly sunny by Tue afternoon,
except afternoon cu buildups will be possible in the L.A./VTU
county mtns. Enough instability should be present to warrant a
slight chance of afternoon showers and thunderstorms over this
area and into the Antelope vly.

The marine layer pattern will continue Tue night into Wed morning,
with varying amounts of low clouds and fog along the coast and
most of the adjacent vlys, including the Salinas River Vly.
Elsewhere and otherwise, mostly clear skies will prevail Tue night
and Wed.

Temps across the region are expected to be several degrees below
normal to near normal on Mon and Tue, with the warmer day overall
on Mon, then turn 4-8 deg below normal for most areas on Wed
thanks to good onshore pressure gradients. Highs in the warmest
vlys and lower mtns on Mon should be in the mid 80s to low 90s,
while on Tue and Wed highs in these areas should be in the mid
80s to around 90.

.LONG TERM (THU-SUN)...11/214 PM.

The 12Z EC and GFS mean ensembles are in a bit better agreement
with the large scale features vs. the deterministic over the
medium range and will focus on these solutions. Overall, it looks
like a broad upper level trof will be over CA Thu, and along and
off the CA coast Fri thru Sun. There should be a broad WSW flow
aloft over the region for the most part thru the period.

Dry weather is expected thru the extended period. The marine
layer pattern will continue Thu thru Sat, with varying amounts of
night and morning low clouds and fog from the coast to the
adjacent vlys. Decent onshore gradients will persist each day,
then weaken for Sat night and Sun with offshore trends. This
should prevent low clouds from developing along the coast at that
time, with mostly clear skies expected for the second half of next
weekend.

Temps will continue to be several degrees cooler than normal Thu,
then warm to near normal to slightly below normal Fri, and near
normal to slightly above normal Sat and Sun. Highs in the warmest
vlys and lower mtns should reach the 80s to around 90 Thu, and mid
80s to mid 90s Fri thru Sun.

&&

.AVIATION...11/1803Z.

At 1720Z at KLAX, there was no marine layer nor inversion.

Low to moderate confidence in TAFs. There is a 40% chance of
MVFR/IFR conds for coastal TAF sites south of pt conception after
10Z Mon. There is a slight chance of thunderstorms everywhere,
but especially in the mtns, the Antelope Valley and the interior
valleys of SLO and SBA Counties Sun afternoon and evening.

KLAX...Moderate confidence in TAF. There is a 20-30% chance of
MVFR/IFR cigs 10-17Z Mon. There is a slight chance of
thunderstorms this afternoon and evening. Moderate confidence any
east wind component will remain below 8 kts.

KBUR...Moderate confidence in TAF. There is a slight
chance of thunderstorms this afternoon and evening.

&&

.MARINE...11/125 PM.

No changes to the marine forecast in the afternoon issuance.

Small Craft Advisory (SCA) conditions are expected to return to
at least the outer waters starting Monday afternoon and may
linger for much of the week. SCA conditions may spread into the
inner waters during the afternoon and evening hours, especially
north of the Channel Islands.

There is a 5 to 15 percent chance (highest inner waters) of a
thunderstorm through this evening. Night to morning low clouds and
patchy fog will likely return by mid-week.

&&

.BEACHES...11/130 PM.

Post-Tropical Cyclone Kay continues to weaken and move southwest
of the region. Elevated swell will continue to subside through the
afternoon, and the Beach Hazards Statement will be allowed to
expire at 2 pm. An increased risk for rip currents still poses a
threat through today.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Flood Watch in effect until 11 PM PDT this evening for zones
      53-54-344-345-353. (See LAXFFALOX).
PZ...NONE.

&&

PUBLIC...Sirard
AVIATION...Sweet/Lund
MARINE...Sweet/Lund
BEACHES...Sweet/Lund
SYNOPSIS...Sirard

weather.gov/losangeles

Experimental Graphical Hazardous Weather Outlook at:
https://www.weather.gov/erh/ghwo?wfo=lox

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
322 PM PDT SUN SEP 11 2022

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

0243 PM     FLOOD            1 WNW LAKE HUGHES       34.68N 118.45W
09/11/2022                   LOS ANGELES        CA   LAW ENFORCEMENT

            REPORT FROM CHP OF SOMEONE STUCK IN THE MUD
            FOLLOWING THUNDERSTORM PASSAGE ON SB LAKE
            HUGHES 2-3 MILES SOUTH OF ELIZABETH LAKE RD
            INTERSECTION.

&&

LP

Special Weather Statement
National Weather Service OXNARD CA
433 PM PDT Sun Sep 11 2022

CAZ038-344-345-353-120015-
San Luis Obispo County Mountains CA-
Santa Barbara County Interior Mountains CA-
San Luis Obispo County Interior Valleys CA-Cuyama Valley CA-
433 PM PDT Sun Sep 11 2022

...A strong thunderstorm will impact portions of north central Santa
Barbara and southeastern San Luis Obispo Counties through 515 PM
PDT...

At 433 PM PDT, Doppler radar was tracking a strong thunderstorm 10
miles west of Cuyama, or 28 miles northeast of Santa Ynez, moving
north at 10 mph.

HAZARD...Wind gusts up to 50 mph and nickel size hail.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects. Minor damage to outdoor objects is
         possible.

Locations impacted include...
Cuyama...
Highway 166 between Twitchell Dam and the Cuyama Valley...
and Carrizo Plain.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

&&

LAT...LON 3489 11971 3489 11985 3491 11991 3513 12000
      3515 11966
TIME...MOT...LOC 2333Z 170DEG 9KT 3495 11980

MAX HAIL SIZE...0.88 IN
MAX WIND GUST...50 MPH

Munroe