318
FXUS66 KLOX 201304
AFDLOX

Area Forecast Discussion...UPDATED
National Weather Service Los Angeles/Oxnard CA
604 AM PDT Fri Sep 20 2024

.SYNOPSIS...20/235 AM.

An early season low pressure system will continue an unsettled
weather pattern across the area today. Shower activity will be
continue for the southern portion of the area today, with showers
becoming more isolated from west to east through the day. Some
showers or thunderstorms could have heavy downpours, and gusty
winds. High pressure will build in over the weekend and bring a
significant warming and drying trend to the region over the
weekend into early next week.

&&

.SHORT TERM (TDY-SUN)...20/409 AM.

An early season trough of low pressure continues to spin over the
southern California bight this morning. Showers and isolated
thunderstorms continue to wrap around into the interior portions
of the area from Kern County this morning. Showers have been
lighter overall versus last evening, but a broad area of negative
lifted index values and 850-500 mb MUCAPE values between 400-900
J/kg remain over the region this morning. Rainfall rates around
0.10 inch/hour have been observed with the band of showers pushing
southwest into the interior portions. Some cooling cloud tops are
being watched closely to the southeast of that line near KTSP
where the best 1000-500 mb calculated lifted index values are
located. This line of showers will be monitored closely as it
pushes toward southwest.

A flood watch remains in effect for the Hurricane, Lake, and
Apache burn scars through 5 am PDT this morning. There is a high
likelihood that the flood watch will be allowed to expire, but the
focus of concern will move to the east as the day progresses.
Precipitable water values are down slightly over yesterday,
ranging closer to 125 percent of normal this morning; but the
latest model solutions suggest a slight uptick in moisture,
ranging closer to 150 percent of normal by this afternoon and
evening over the eastern San Gabriel mountains and into the San
Bernardino County mountains. This area of concern for later today
would include where the Bridge Fire is currently burning. WPC is
indicating a marginal chance of excessive rainfall for this region
later today. The latest NCEP high-resolution FV3 solutions
suggest 3 hour rainfall values up to 0.40 inch near the Post Fire
burn scar, then much higher values into the San Bernardino County
mountains as the day progresses. There is a 30 percent chance
localized flash flooding and debris flows could occur across the
Post and Bridge fires later today, but there is not enough
confidence yet to expand the watch to the east.

A mostly north to south flow on the back side of the low pressure
trough will steer any shower activity from the mountains into the
valleys and coastal areas later today and into this evening. The
trough`s slower movement has contributed to PoPs being held on for
longer the system has slowed down. The highest PoPs are indicated
over the mountains and into the foothills of the mountains, but
showers and thunderstorms pushing into Southland valley area and
into the Ventura County coastal plain seems elevated in
confidence at this point.

Otherwise, a cooler air mass will continue across the area
through tonight as a deep marine layer depth will remain in place.
Clouds are pushing well into the coastal slopes of the mountains
this morning, even with the disturbed and weaken marine inversion
over the region at this time.

A marginally tight northerly surface gradient could bring some
sub-advisory northwest to north winds across southern Santa
Barbara County mountains this evening and through the Interstate 5
Corridor tonight. Gusts to between 30 and 40 mph will likely be
observed with local gusts up to 45 mph in a few spots.

A drying and warming trend will take place over the weekend as the
upper-level trough will move off to the east. High pressure aloft
will nose into the region and bring much temperatures, especially
Sunday and Monday. Night through morning low clouds and fog should
remain in the forecast for tonight, then much less marine coverage

.LONG TERM (MON-THU)...20/357 AM.

The latest forecast ensembles agree that Monday will likely be
the warmest day of the week. Low cloud coverage could end up being
confined to the coast by Monday morning as onshore flow weakens.
There is still a large spread of solutions for the remainder of
next week, the forecast ensembles lean trend toward a cooling
trend for Tuesday and Wednesday. The forecast temperatures break
away from NBM values for Monday, but otherwise, keeps the NBM
values for now. Forecast ensemble leans towards a cooler air mass
with more marine influence for Tuesday, Wednesday, and Thursday.

&&

.AVIATION...20/1301Z.

At 1216Z at KLAX, there was a deep moist layer up to 5000 feet.
The top of the inversion was at 5500 feet with a temp of 11 C.

Moderate confidence in TAFs for KPMD and KWJF. There is a 20% chc
of TSTMs thru 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, there is a 30% chc of IFR conds after 06Z Sat.

For KSMX and KSBP, low confidence in cig height and timing. LIFR
conds possible (20% chc) thru 17Z, with VLIFR conds possible (20%
chc) after 06Z Sat.

For KSBA, and Ventura and Los Angeles County TAFs, there is a
20-30% chance of -DZ or -SHRA at all sites thru 00Z, and a 10-20%
chance of thunderstorms between thru 00Z. The highest chances
will be for KSBA, KOXR, KBUR, and KVNY.

Any thunderstorms that form may produce brief +RA and gusty,
erratic winds.

KLAX...Low confidence in TAF. Cigs may vary between BKN015-035
frequently thru at least 18Z, and there is a 30% chc of
-SHRA and a 15% chance of TSTMs thru 15Z Fri-00Z Sat. Low
 confidence in hgt of CIGs after 06Z sat, which could be between
 Bkn008-018. No significant east wind component expected.

KBUR...Low confidence in TAF. Cigs may vary between BKN015-035
frequently thru at least 18Z. There is a 20% chance of TSTMs
15Z Fri-00Z Sat. Low confidence in hgt of CIGs after 06Z sat,
which could be between Bkn008-015.

&&

.MARINE...20/312 AM.

Isolated thunderstorms will be possible across the eastern portion
of the Santa Barbara Channel to Point Dume and out to Santa Cruz
Island into the afternoon. Any thunderstorm that forms has the
potential for frequent cloud to surface lightning, gusty and
erratic winds with rough seas, and small hail.

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 of SCA level winds this
afternoon thru evening. For the southern zones (Pt Sal to San
Nicolas Island), there is a 60% chance of SCA winds this afternoon
through late tonight across the waters from Point Conception to
San Nicolas Island. Saturday through Tuesday, moderate to high
confidence in winds and seas remaining below SCA levels.

For the inner waters along the Central coast, high confidence in
conds remaining below advisory levels through Tuesday.

For the Santa Barbara Channel, low confidence in the wind forecast
for today. There is a 40-50% chance of SCA level wind gusts
across the extreme western portion of the channel this afternoon
through evening with a 20% chance of winds extending into the
eastern portion. Held off on issuing an advisory due to highest
chance of SCA level winds remaining confined to the extreme
western portion. Then, moderate confidence in conditions
remaining below SCA levels through Tuesday.

For the inner waters off the coast of LA and Orange Counties,
high confidence in conditions remaining below advisory levels
through Tuesday. However, low end SCA level gusts are possible
(20-30 percent) in this afternoon through evening in the San
Pedro Channel.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...Small Craft Advisory in effect from 3 PM this afternoon to 3
      AM PDT Saturday for zones 673-676. (See LAXMWWLOX).

&&

$$

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

weather.gov/losangeles

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