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471
FXUS66 KLOX 192102
AFDLOX

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

.SYNOPSIS...
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19/126 PM.

An unsettled weather pattern will develop across the region
through Friday as an early season low pressure system moves over
the region. A cool air mass will remain in place through Friday,
but turn more showery through tonight. 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
into Friday before the low pressure area and the associated air
mass exits the region. A significant warming and drying trend
will develop over the weekend and into early next week.
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&&

.SHORT TERM (TDY-SUN)...
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19/153 PM.

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.
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&&

.AVIATION...19/1834Z.

At 1653Z at KLAX, there was a 4500 ft deep moist layer. The top
of the weak marine inversion was at 5500 feet with a temperature
near 10 degrees Celsius.

High confidence in TAFs for KPMD and KWJF.

Low confidence in remaining TAFs. Cig heights will vary
frequently due to presence of upper level low moving over the
region. Timing of flight cat and VCSH/VCTS changes could be off by
+/- 5 hours.

For KPRB, TSTM (30% chc) and rain shower 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, with highest chances
thru 06Z. There is also a 20-40% chance of isolated thunderstorms
thru 12Z, with best chances at KSMX and KSBP before 06Z. LIFR
conds possible (30% chance) at KSBP and VLIFR conds possible (30%
chance) at KSMX from 10Z thru 17Z. There is a 20% chance of brief
IFR cigs at KSBA between 08Z and 16Z.

For Ventura and Los Angeles County TAFs, there is a 20-30% chance
of -DZ is possible at all sites from 00Z thru the remainder of the
period tomorrow. During this period, there is also up to a 20%
chance of isolated thunderstorms. For KOXR and KCMA, there is a
40% chance that conds remain MVFR or VFR thru the period.

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

KLAX...Low confidence in TAF. There is a 40% chance that cigs
below BKN035 will arrive +/- 3 hours from current forecast. Cigs
may vary between BKN015-035 frequently from 04Z thru at least 18Z.
There is a 30% chance of -DZ from 04Z through 18Z, and a 20%
chance of isolated thunderstorms during this period. No
significant east wind component is expected.

KBUR...Low confidence in TAF. There is a 40% chance that cigs
below BKN035 will arrive +/- 3 hours from current forecast. Cigs
may vary between BKN015-035 frequently from 04Z thru at least 18Z.
There is a 10% chance of brief BKN008-010 cigs between 04Z to
17Z. There is a 30% chance of thunderstorms from 04Z to 18Z.

&&

.MARINE...
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19/201 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 tomorrow, and thru this
afternoon for the southern zones (Pt Sal to San Nicolas Island).
There is a 40-50% chance for SCA level winds tonight in the two
southern zones, mostly from Pt Conception to San Nicolas Island,
thus an SCA is out for this period. Tomorrow there is a 50-60%
chance for more widespread SCA winds tomorrow afternoon thru late
night in these zones. 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, moderate to high
confidence in the forecast. There is a 20% chance for brief
isolated low end SCA level winds late tonight. Otherwise, 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 40-50% chance of SCA level wind gusts,
mostly in the western portion of the channel this afternoon thru
evening. There are higher chances in the same areas tomorrow
afternoon thru late night (50-60%). 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 in the afternoon
thru evening today and 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 tonight thru tomorrow
morning. A Marine Weather Statement is in effect to communicate
the hazards from thunderstorms to the marine community.
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&&

.LOX WATCHES/WARNINGS/ADVISORIES...
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CA...Flood Watch in effect through late tonight 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).
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&&

$$

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

weather.gov/losangeles

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