Montebello, California Weather Forecast Discussion

456
FXUS66 KLOX 181219
AFDLOX
Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
519 AM PDT Thu Sep 18 2025
.SYNOPSIS...18/518 AM.
The remnants of Tropical Storm Mario will continue to move over
the region through Friday. A moist air mass in place will bring
showers with isolated to scattered thunderstorms to region. While
temperatures will be cooler due to cloudy skies and showers,
areas that receive any sunshine during the day will heat up
rapidly. Some drying will take place over the weekend, but there
is slight chance of showers as additional moisture from the south
arrives. Temperatures will be near normal and the muggy weather
will continue into early next week.
&&
.SHORT TERM (TDY-SAT)...18/517 AM.
Showers and isolated thunderstorms continue to move north across
southern California this morning as moisture and instability with
the remnants of former Tropical Storm Mario tracks north. A very
moist air mass is in place already with precipitable water values
approaching 2 inches this morning, or about 200 to 250 percent
normal. Most areas across the Southland have seen light amounts
overnight with some isolated heavier cells occasionally. Rainfall
amounts are generally a tenth of an inch or less with local
amounts up to 0.25 inch. An early band of showers brought locally
heavier rainfall to the offshore islands and amounts climbed to
0.40 inch. While lightning strikes have been more isolated
overnight, solar insolation with daytime heating will steepen
lapse rates and very likely bring back a larger areal coverage of
thunderstorms. While confidence in high precipitation in
continuing to spread north, there is a chance that PoPs could be
overdone this afternoon and evening as a break in the action
occurs. Daytime heating and sunshine could produce a much more
intense convective activity as the day progresses. With the very
moist air mass in the place and the threat of thunderstorms
developing, heavy rainfall is possible with any thunderstorms in
addition to dangerous lightning, and gusty and erratic winds. A
Flood Watch remains in effect through early Friday morning.
As the system is convective, this storm will be different from our
normal winter storms and monsoonal flow induced afternoon
convection. While most areas will get at least some rain today,
some areas may get little to none. Still, others just a short
distance away could have flooding. Rainfall rates capable of
causing flash flooding, mud, and debris flows have already
occurred earlier this morning, and daytime heating will only serve
to destabilize the environment later today.
Showers will continue on and off through late tonight and into
Friday, then convective activity should become confined to the the
higher terrain. Showers should reduce in coverage through the day
across the coastal and valley areas, but afternoon heating will
drive another round of showers and thunderstorms over thew
mountains and desert. With more sunlight and daytime heating,
brief heavy rainfall cannot be ruled out as less cloudiness could
promote a more unstable lapse rate to develop.
A slightly warmer and drier pattern should develop Saturday.
.LONG TERM (SUN-WED)...18/515 AM.
Forecast ensembles lean toward a drier day on Sunday with a few
degrees of warming, there is a moderate chance that another
moisture surge from the south could bring some showers and
thunderstorms with locally heavy rain between Monday and Tuesday.
An upper low meandering down the West Coast could ingest some
subtropical moisture with a shortwave trough off Cabo San Lucas
and bring it northward. This could happen as early as Sunday
afternoon, but more likely not until Monday afternoon. Confidence
is remains low at this point, but there are low chances of showers
in the forecast for early next week.
The latter part of next week looks warm and dry. There is a
moderate chance that a heatwave could develop for the latter half
of next week, but the spread across the model solution is pretty
wide at this point.
&&
.AVIATION...18/0608Z.
At 0455Z at KLAX, the marine layer was at 700 feet. The top of
the inversion was 1500 feet with a temperature of 22 C.
Overall, low to moderate confidence in 06Z TAF Package. Have
pushed back onset of showers a few hours from previous package.
Generally VFR conditions with brief periods of IFR-MVFR CIG/VSBY
restrictions under heavy rainfall. IFR CIGs due to marine layer is
possible at KSBP & KSMX through 12Z Thursday. Low confidence in
wind speed/direction & timing of wind shifts. Wind shifts could be
sudden and highly variable. Thunderstorms are possible through
period.
KLAX...Low to Moderate confidence in 06Z TAF. There is a 20%
chance of thunderstorms through 13Z Thursday - which could bring
brief periods of IFR to MVFR conditions. There is a likely chance
(70%) that easterly winds exceed 7 knots from 12Z to 20Z Thursday.
KBUR...Low to Moderate confidence in 06Z TAF. There is a 20%
chance of thunderstorms from 09Z to 14Z Thursday - which could
bring brief periods of IFR to MVFR conditions.
&&
.MARINE...18/519 AM.
Low confidence in forecast for winds and seas into Thursday
morning, then moderate confidence thereafter.
The remnants of former Tropical Storm Mario will affect the
Southern California coastal waters through Friday. Showers with
isolated to scattered thunderstorms can be expected with the
highest chances of impacts through Thursday night. Any
thunderstorms that develop will be capable of gusty and erratic
winds, locally rough seas, frequent and dangerous lightning, and
brief heavy rain. Additionally, waterspouts cannot be ruled out
entirely. Please monitor the forecast if you have any plans on
going out on the water this week.
Small Craft Advisory (SCA) level winds and choppy seas will
likely continue across the waters from Point Conception to San
Nicolas Island and across the Southern California Bight through
late this morning. Winds may shift in direction and speed rapidly
as the system continues to move through the region.
Winds and seas should fall below SCA levels late this morning and
very likely remain below SCA levels through Saturday. Winds will
increase and approach SCA levels Saturday afternoon through at
least Tuesday night. Lulls in the winds are possible during the
late night and early morning hours. The strongest winds will be
initially focused from Point Conception to San Nicolas Island and
the western portion of the Santa Barbara Channel, then expanding
to the rest of the outer waters and nearshore Central Coast waters
Sunday.
&&
.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Flood Watch in effect through late tonight for zones
      38-344-345-353-362-369-370-376>383-548. (See LAXFFALOX).
PZ...Small Craft Advisory in effect until 9 AM PDT this morning
      for zones 650-655-673-676. (See LAXMWWLOX).
&&
$$
PUBLIC...Hall
AVIATION...Black
MARINE...Hall
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