083
FXUS66 KLOX 200313
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
813 PM PDT Thu Sep 19 2024

.SYNOPSIS...19/715 PM.

An unsettled weather pattern will persist through Friday as an
early season low pressure system moves over the region. While not
every location will see showers and thunderstorms, any shower
activity will be capable of producing heavy rainfall, especially
across interior portions of Ventura, Santa Barbara, and San Luis
Obispo Counties through this evening. Some showers or thunderstorms
could linger through Friday morning, before the low pressure
system exits the region. A significant warming and drying trend
will develop over the weekend into early next week.

&&

.SHORT TERM (THU-SUN)...19/811 PM.

***UPDATE***

The upper low moving across the region is currently centered near
Point Conception, and will continue to shift southeastward along
the coast through late Friday morning. An area of strong
thunderstorms developed over the interior of Santa Barbara and San
Luis Obispo Counties this afternoon into the early evening hours.
The strongest storms produced heavy downpours and small hail,
with rain rates of 1 to 2 inches per hour. Rainfall observations
in the area were mostly light, up to 0.10 inch, but the stronger
storms produced between 0.45 to 0.78 inches of rain. Roadway
flooding and landslides were reported from Highway 166 in an area
that received persistent, heavy rainfall.

Radar images as of 800 PM show the activity has diminished
significantly, however localized flooding or landslides may be
possible in areas that had the heavier rain. As the low moves
along the coastline overnight, the threat of showers and
thunderstorms will shift to Ventura and L.A. Counties. Shower
activity will likely be isolated to scattered, and many areas may
not see any rain. However, there is potential that heavy rain will
affect some locations through around noon Friday. Models indicate
that the steering flow aloft will be stronger, so that storms will
not be stationary, helping to decrease the likelihood of flooding
issues.

Friday afternoon will see showers decreasing and with partial
clearing and warming. Highs will bump up on average 4 to 8 degrees
compared to today`s high temperatures.

***From Previous Discussion***

An unseasonably cold upper low is located just west of the Central
Coast this afternoon. Earlier this morning there were some
thunderstorms that developed across the northern interior of SLO
County. Hi res models were accurate depicting a lull in the
activity through the rest of the morning and early afternoon. But
now with the afternoon heating and cooler air aloft we`re starting
to see some building cumulus clouds that should develop into
showers and thunderstorms over the next couple hours and into the
evening across Santa Barbara and SLO Counties, especially over the
elevated terrain. HREF models continue to focus in on the area
around the interior SLO/SBA County border as the most likely
location for stronger storms and heavier rainfall, but certainly
can`t rule out strong storms in other parts of those counties as
well as northern Ventura County. Not all areas will get rain, but
in the most favorable areas rainfall rates up to an inch per hour
are possible with hail and gusty winds as well. Hi res models are
also indicating some rotation potential with these storms so there
is a non-zero threat of a funnel cloud or small tornado. A flood
watch was issued earlier for the Hurricane and Apache burn scars,
however, as the system has shown a slightly farther west
trajectory it was decided to include the Lake burn scar near the
Santa Ynez Valley, and extend the time through 5am Friday morning.

The upper low is expected to turn east as it rounds Pt Conception
tonight and follow the coastline into Orange County Friday
morning. As this happens, the threat for active weather, showers
and thunderstorms will increase south of Pt Conception. Again, not
everywhere will get rain, but where it does rain there is a
potential for high rain rates. Steering flow increases as the low
starts to move east which would limit rain amounts in any one area
so for now there are no flood watches south of Pt Conception
except for the northern Ventura County mountains tonight. By
Friday afternoon most if not all the shower/storm activity should
be east of Ventura County, and east of LA County by around 6pm
Friday.

Saturday and Sunday will be dry and clear with significant warming
by Sunday, especially inland. Valley highs expected to be back in
the 90s Sunday while inland coastal areas are in the low to mid
80s. Minimal if any marine layer expected following the storm.

.LONG TERM (MON-THU)...19/201 PM.

Warm weather to peak Monday and Tuesday with some cooling back to
normal levels expected mid to late week. There is a larger spread
of possible solutions later next week as some of the ensemble
runs are indicating the ridge more or less continuing while others
show a weak trough coming in Thu/Fri that would bring additional
cooling. Neither solution is extreme in any way so impacts would
be minimal and certainly dry weather expected. Longer rain
projections show little or no chance of any additional
precipitation beyond Friday through the early part of Oct.

&&

.AVIATION...20/0022Z.

At 1653Z at KLAX, there was a deep moist layer up to 4300 feet.
The top of the inversion was at 6200 feet with a temperature near
10 degrees Celsius.

Moderate to high confidence in TAFs for KPMD and KWJF, with the
reduced confidence due to a slight chance of thunderstorms in the
vicinity between 10Z to 21Z.

Low confidence in remaining TAFs. Cig heights will vary frequently
due to an upper level low moving over the region. Timing of
flight cat and VCSH/VCTS changes could be off by +/- 4 hours.

For KPRB, TSTM (30% chc) and SHRA chances diminish after 06Z.

For KSMX, KSBP, and KSBA, low confidence in cig height and timing.
Thru 12Z, there is a 20-40% chance of -DZ or -SHRA, with highest
chances thru 06Z. There is also a 20-40% chance of thunderstorms
thru 12Z, with best chances at KSMX and KSBP before 06Z. LIFR
conds possible (20% chance) at KSBP and VLIFR conds possible
(20-30% chance) at KSMX from 10Z thru 17Z.

For Ventura and Los Angeles County TAFs, there is a 20-30% chance
of -DZ or -SHRA at all sites from 00Z thru the remainder of the
period, and a 20% chance of thunderstorms between 06Z-18Z.

Thunderstorms may produce brief +RA and gusty, erratic winds.

KLAX...Low confidence in the 00Z TAF. Cigs may vary between
BKN015-035 frequently from 04Z thru at least 18Z, and there is a
30 percent chance of -SHRA and a 20% chance of thunderstorms
during this period. No significant east wind component expected.

KBUR...Low confidence in the 00Z TAF. Cigs may vary between
BKN015-035 frequently from 04Z thru at least 18Z. There is a 30%
chance of thunderstorms from 04Z to 18Z.

&&

.MARINE...19/713 PM.

For the Outer Waters (Central coast south to San Nicolas
Islands), moderate to high confidence in the forecast. High
confidence in winds and seas remaining below Small Craft Advisory
(SCA) level thru early next week in the northern zone (off the
Central Coast) except for a 20-30% chance for SCA level winds in
the afternoon thru evening hours Friday. For the southern zones
(Pt Sal to San Nicolas Island) there is a 50-60% chance of SCA
level winds through late tonight. There is a 60% chance of more
widespread SCA winds tomorrow afternoon thru late night over the
waters near Point Conception. From Sat thru Tues, moderate to
high confidence in winds and seas remaining below SCA level in the
southern outer waters.

For the inner waters along the Central coast, high confidence in
winds remaining sub advisory level thru early next week.

For the Santa Barbara Channel, moderate confidence in the
forecast. There is a 50-60% chance of SCA level wind gusts,
mostly in the western portion of the channel tomorrow afternoon
thru late tomorrow night. Then, moderate confidence in conditions
remaining below SCA level Sat thru Tues.

For the inner waters off the coast from LA and Orange County, high
confidence in conditions remaining sub advisory level thru early
next week. Low end SCA level gusts are possible (20-30 percent) in
the afternoon thru evening hours tomorrow, isolated to the San
Pedro Channel.

Isolated to scattered thunderstorms will be possible across all
of the coastal waters through tomorrow morning, as an upper level
low pressure system moves from off the Central Coast thru
Southwestern California. The trough will move southeastward
across the southern California bight tonight and onshore over
southern California through Friday. The northern waters have a
greater chance to be impacted thru late tonight, while the
southern zones have a better chance from late tonight thru
tomorrow morning. A Marine Weather Statement is in effect to
communicate the hazards from thunderstorms to the marine
community.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Flood Watch in effect until 5 AM PDT Friday for zones
      38-344-345-348-353-377. (See LAXFFALOX).
PZ...Small Craft Advisory in effect until 3 AM PDT Friday for
      zones 650-673-676. (See LAXMWWLOX).

&&

$$

PUBLIC...MW/Smith
AVIATION...Lewis/Smith
MARINE...Lewis/Smith
SYNOPSIS...Smith

weather.gov/losangeles

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