San Marino California Weather Forecast Discussion

907
FXUS66 KLOX 131807 AAA
AFDLOX
Area Forecast Discussion...UPDATED
National Weather Service Los Angeles/Oxnard CA
1107 AM PDT Mon Oct 13 2025
updated aviation discussion
.SYNOPSIS...13/330 AM.
An early season storm system in the Pacific Northwest will dig
south into the region through Tuesday. Periods of rain and high
elevation snow, heavy at times, will develop from north to south
from this afternoon through Tuesday. Gusty southerly winds are
likely to develop this evening through Tuesday ahead of and along
the system`s cold front. Cooler temperatures with drier
conditions will linger into Thursday, then a warming trend will
develop for the end of the week.
&&
.SHORT TERM (TDY-WED)...13/917 AM.
***UPDATE***
The forecast remains generally on track. The peak of the storm
remains focused on tonight through Tuesday afternoon. There may
be a few modifications to the finer details based on the early
assessments of the latest projections. Rain rate forecasts will
likely be increased, especially for any south and southwest facing
slopes. Nearly every high resolution model is showing streaks of
heavy rain moving through the region, and while not every area
will see them, these narrow bands could happen anywhere. Several
of the projections are now showing the rain the organizing and
intensifying as it swings into LA County, which is concerning for
the recent burn scars - especially the Eaton and Bridge scars.
The severe weather threat also remains. Still seeing several
signatures (the trajectory of the low, the diffluence aloft, the
high shear environment) for supercell thunderstorms with several
high resolution models resolving finer scale parameters conducive
of isolated strong downdraft winds and/or weak tornadoes (updraft
helicity being one of them).
What should people do? For tonight through Tuesday: Avoid outdoor
activities and stay indoors as much as possible, especially if
you hear thunder, see lightning, or experience sudden wind
shifts. Avoid parking near tall trees. Be ready for sudden power
outages. Avoid the roads as much as possible, and if you have to
drive, allow extra time as traffic will be increased due to
slippery roads, low visibility, and localized flooding. If you are
near a burn scar, there is a risk of significant debris flows.
Heed the advice of local officials, and expect at the very least
mud and debris on some roads. Boaters, please stay in safe harbor.
For everyone, stay tuned to your local news outlet and
weather.gov for any updates.
***From Previous Discussion***
The latest satellite imagery shows an upper-level trough digging
south off the Oregon coast early this morning. A cold frontal
boundary can be seen stretching from near Portland, Oregon out to
the southwest and west. This frontal boundary and the associated
upper-level trough will dig south through Tuesday, bottoming out
over Central California Tuesday afternoon. Light to moderate pre-
frontal rain could start over the Southland as early as this
evening, but the heaviest rainfall is expected along the cold
front, which will arrive along the Central Coast late this
afternoon and early this evening. With high-resolution multi-model
ensemble members all indicating rain spreading over the region
spreading north to south from this afternoon through Tuesday
afternoon, PoPs have been nudged higher to between 90 and 100
percent along the frontal boundary. Virtually every location in
the four county area will receive measurable rainfall through
Tuesday morning.
Storm total rainfall amounts are expected to range from 0.75 inch
to 1.50 inches for the coastal and valleys with up 1.50 to 3.00
inches in the mountains. Local amounts to 4.00 inches are possible
along south-facing slopes across the Southland and into Santa
Ynez Range in Santa Barbara County. There is less certainty with
convective elements of the band, but there is moderate to high
confidence that a burst of heavy rainfall with a quasi-linear
convective system (QLCS) will develop overnight tonight into
Tuesday. Rainfall totals could go higher than the range stated if
the front slows down over the region and could be less than the
range stated if the front accelerates through the region. A
difluent flow pattern aloft will aid lift as the front approaches
the region and possibly allow for isolated thunderstorms to
develop. Rainfall rates will generally range between 0.25-0.50
inch per hour, but some of the higher resolution models continue
to indicate potentially higher rates of 0.50-1.00 inch per hour or
greater. Sub-hourly rates could be quite intense with the
possibility that some locations could receive a third to two-
thirds of an inch of rainfall in a very short time. A Flood Watch
remains in effect for the recent burn areas from 8 pm tonight
through 3 pm Tuesday as rainfall rates could reach or exceed USGS
thresholds for area burn scars. Significant mud and debris flows
from recent burn scars, including the Gifford, Madre, Lake,
Palisades, Franklin, Eaton, and Bridge burn scars could develop.
With the difluent flow pattern aloft and the thunderstorm
potential in place, periods of heavy rainfall, dangerous
lightning, and gusty winds will be in play with this storm.
Marginal wind shear parameters are present for the potential for
weak tornadoes or waterspouts to develop tonight along the Central
Coast and late tonight and early Tuesday morning along the South
Coast of California. Slightly more favorable directional and speed
shear develops across the Southland after midnight tonight
through mid- morning on Tuesday. The topographic features of the
Los Angeles Basin and the Greater South Coast Basin can enhance
wind shear parameters and aid tornadic development in storms. As
colder air mass aloft moves into the region on Tuesday afternoon
and evening, the potential for brief heavy downpours with small
hail could enter the picture, while gusty and erratic winds and
dangerous lightning will continue to be hazards.
Southerly winds will increase through today and tonight ahead of
the front. There is the possibility of high wind warning level
winds across the mountains tonight and into Tuesday morning,
especially given the possibility of the QLCS moving over the
region tonight. Downburst winds with the convective system, should
it develop, could down trees, tree limbs, and power lines. For
now, a wind advisory was added for the Antelope Valley and
adjacent foothills from noon today through 10 pm tonight for pre-
frontal winds. The greatest area of concern would be the
potential for mountain wave activity along the interior slopes of
the San Gabriel Mountains this afternoon and evening. Foothill
communities such as Valyermo, Pearblossom, Crystalaire, and Lake
Palmdale may be particularly vulnerable given the wind direction.
With colder air aloft moving in along the front, light to moderate
snowfall accumulations are possible above the 6000 foot elevation
level and when combined with the winds along the front, travel
could end up being treacherous at times on high mountain
roadways, such as the Angeles Crest Highway and Lockwood Valley
Road. A Winter Weather Advisory was considered for the higher
elevations of the San Gabriel Mountains and the Ventura County
mountains, but given the marginal conditions, the decision was
tabled for now to allow for more data to arrive. Snowfall amounts
could range between 1 and 4 inches with this storm with isolated
amounts up to 6 inches.
There is an outside chance that the shower threat could linger
across the Los Angeles Basin into Wednesday as the trailing vort
max moves over the region. Drier conditions should develop
through the day with cooler temperatures lingering across the
region for Wednesday.
.LONG TERM (THU-SUN)...13/331 AM.
Weak to locally moderate offshore flow should set up between
Wednesday night and into Thursday morning. Currently, winds look
to be sub-advisory for Thursday morning and no advisories looks to
issued. The first frost of the season could occur for some
interior valley and wind sheltered areas on Thursday morning as
clear skies will make radiative cooling processes much more
efficient. Patchy frost was added to a few spots in the Antelope
Valley and the San Luis Obispo County interior valleys, but this
will need to looked at closer as we move forward into the week.
Otherwise, high pressure aloft building into the region will bring
a warming trend for late week. Temperatures could warm to near
normal on Friday or Saturday.
&&
.AVIATION...13/1805Z.
At 1715Z at KLAX, the marine layer was 5000 ft deep. The top of
the inversion was near 5800 ft with a temperature of 8 deg C.
Low confidence overall in the 18Z TAFs.
Expecting SHRA after 00Z Tue along Central Coast and after about
03Z-05Z for VTU/L.A. Counties with MVFR conditions at times.
Around a 40% chance of TSRA during this timeframe for KPRB, KSBP,
KSMX, & KSBA, with a 20%-30% chance elsewhere later this evening
thru late tonight. Expect visibility reductions under heavy
rainfall. Brief IFR conditions cannot be ruled out.
LLWS and turbulence is possible as front approaches and near any
thunderstorms that develops.
Low to moderate confidence in wind forecasts. Wind gusts may be
off 5 to 10 knots and/or direction by 30 degrees, especially for
coast and valley sites after 00Z Tuesday - as front approaches.
KLAX...Low to moderate confidence in the 18Z TAF. MVFR CIGs 015-
025 common thru much of the period. Reduced visibility due to
heavy rainfall likely as strong storms arrive with front.
Conditions may fall to IFR at times with the front later tonight.
There is a 20%-30% chance of a thunderstorm from 05Z to 13Z Tue.
There is a 90% chance of an east wind component reaching up to 15
knots thru 21Z today, and a 40% chance of an east wind component
of 10-15 knots at times 05Z-18Z.
KBUR...Low to moderate confidence in 18Z TAF. Reduced visibility
due to heavy rainfall likely as strong storms arrive with front.
Conditions may fall to IFR at times from 06Z to 15Z Tuesday.
20%-30% chance of a thunderstorm 06Z-12Z tonight.
&&
.MARINE...13/830 AM.
This afternoon through Tuesday afternoon, a storm system and
associated cold front will move across the region. This will bring
a 20-40% chance of thunderstorms across all the coastal waters
during that timeframe. Any thunderstorms that form may be capable
of frequent cloud to surface lightning, gusty and erratic winds,
small hail, and even a waterspout. Please see the latest Marine
Weather Statement (LAXMWSLOX) for further details.
Small Craft Advisory (SCA) level seas over the outer waters will
diminish this afternoon. SCA winds are possible (50% chance) with
the cold front later tonight into Tuesday morning, then
decreasing from the west behind the front late Tuesday morning
through Tuesday night. Wednesday through Thursday increasing NW
winds will likely reach SCA levels once again. Best chances south
of Point Conception.
For the inner waters south of Point Conception, S to SW winds
increasing to SCA levels are expected across the area mainly
tonight into Tuesday morning as the front approaches and moves
through the region.
&&
.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Flood Watch remains in effect from 8 PM PDT this evening
      through Tuesday afternoon for zones
      38-88-342-344-345-348-353-355-358-362-368>375-377>380-548.
      (See LAXFFALOX).
     Wind Advisory in effect until 10 PM PDT this evening for
      zones 381>383. (See LAXNPWLOX).
PZ...Small Craft Advisory in effect until noon PDT today for zone
      676. (See LAXMWWLOX).
&&
$$
PUBLIC...Hall/Kittell
AVIATION...Sirard
MARINE...Sirard
SYNOPSIS...Hall
weather.gov/losangeles
Experimental Graphical Hazardous Weather Outlook at:
https://www.weather.gov/erh/ghwo?wfo=lox

NWS LOX Office Area Forecast Discussion