Rancho Park, California Weather Forecast Discussion

097
FXUS66 KLOX 180403
AFDLOX
Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
903 PM PDT Wed Sep 17 2025
.SYNOPSIS...17/124 PM.
It will be warm and muggy through Friday as remnants of tropical
storm Mario move into the area. Temperatures will cool through the
period but humidities will be much higher than normal. Rain and
thunderstorm chances will begin Wednesday night and continue into
at least early Friday. Over the weekend into early next week 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 (WED-SAT)...17/902 PM.
***UPDATE***
Today saw quite a bit of convection, with showers and
thunderstorms initiating over the mountains of Los Angeles and
Ventura Counties, spreading into San Luis Obispo and Santa Barbara
Counties. Activity has quieted down this evening, with the next
batch of showers and thunderstorms expected to move into the
coastal waters from the south in the early morning hours. However,
currently not seeing much of a northerly motion from the southern
showers just south of our coastal waters. Lower confidence in
timing, as guidance continues to push back the arrival of this
rain band, so adjustments may be needed to account for this.
Otherwise, the forecast looks on track.
***From Previous Discussion***
Very tropical conditions will dominate the weather conditions
across southern California through at least Friday. The leading
edge of the moisture and instability arrived this morning
triggering isolated showers and thunderstorms as far north as SLO
County, but so far mostly confined to the coastal waters and the
mountains. As PW`s continue to increase tonight into Thursday and
additional triggering factors arrive including better forcing
aloft and overall more unstable conditions, showers and
thunderstorms will become more widespread and not confined to the
higher terrain.
It`s important to understand that this pattern is very different
from a traditional winter storm and even from our typical summer
afternoon convection. While most areas will get at least some
rain, some areas may get little to none, while others just a short
distance away could have flooding. A Flash Flood Watch has been
issued and begins late tonight and continues until early Friday
morning. This is based on the latest CAMs guidance, some of which
do show heavy showers developing as early as around 3am Thursday.
Models have been consistent showing pockets of very heavy rain
once the system is over our area, and some storms could just
develop anywhere with little advance notice. So people near
sensitive areas, including burn scars, need to be ready to move at
a moment`s notice.
While lightning over the coastal waters has dropped off this
afternoon, this is a common pattern during the daytime and more
strikes are expected again overnight as the deeper moisture
arrives.
Shower and thunderstorm chances will decrease later Thursday
night into Friday morning and most of the precipitation should be
done by Friday afternoon or evening.
Dry and slightly warmer conditions are expected Saturday with more
sunshine and lowering humidities.
.LONG TERM (SUN-WED)...17/214 PM.
The most likely outcome for Sunday is a quiet weather day with 2-4
degrees of warming, bringing highs to around normal in most areas.
However, there are still a around 10% of the ensemble solutions
that show the beginning of another moisture surge from the south
and some possible showers and thunderstorms with locally heavy
rain. The moisture source comes from the next tropical wave moving
off MX. At the same time many of the models are showing another
upper low meandering down the West coast along 130n. As the low
moves farther south, some of the models are entraining some of
the moisture from the tropical wave and bringing it towards
southern California. This could happen as early as Sunday
afternoon, but more likely not until Monday afternoon. There are a
lot of moving parts to this so confidence is very low. For now
there are small rain chances both Sunday and Monday.
There are also some solutions that keep the upper low farther
offshore, creating strong high pressure over the area with a
warming trend. Stay tuned.
&&
.AVIATION...17/1657Z.
At 1630Z at KLAX, the marine layer depth was around 500 feet.
The top of the inversion was 2500 feet with a temperature of
26 degrees Celsius.
Overall, moderate confidence in 18Z TAF package. With surge of
subtropical moisture through the period, general VFR conditions
are expected at all sites. There will be the potential for
widespread showers and scattered thunderstorms at all sites
through the period. This shower/thunderstorm activity could
produce brief period of IFR to MVFR CIG/VSBY restrictions.
KLAX...Moderate confidence in 18Z TAF. There is a 20% chance of
thunderstorms after 00Z which could bring brief periods of IFR to
MVFR conditions. There is a 20% chance of easterly winds around 7
knots after 06Z.
KBUR...Moderate confidence in 18Z TAF. There is a 20% chance of
thunderstorms after 00Z which could bring brief periods of IFR to
MVFR conditions.
&&
.MARINE...17/820 PM.
The remnants of former Tropical Storm Mario will affect the
Southern California coastal waters through Friday. Showers and
scattered thunderstorms can be expected through Friday 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.
Low confidence in forecast for winds and seas overnight into
Thursday morning, then moderate confidence thereafter. Small Craft
Advisory (SCA) level winds and choppy will likely continue across
the waters from Point Conception to San Nicolas Island, and
across the Southern California Bight overnight into the early
morning hours. Winds may shift in direction and speed rapidly as
the system continues to move through the region. Then, moderate
confidence in sub- advisory conditions through Saturday morning.
Winds will increase and approach SCA levels Saturday afternoon
through at least Monday night, with relative lulls each morning.
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, although there is a low
chance of SCA level winds in this area Saturday evening.
&&
.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Flood Watch in effect from 5 AM PDT Thursday through late
      Thursday night for zones
      38-344-345-353-362-369-370-376>383-548. (See LAXFFALOX).
PZ...NONE.
&&
$$
PUBLIC...Phillips/MW
AVIATION...RAT
MARINE...Lewis
SYNOPSIS...MW
weather.gov/losangeles
Experimental Graphical Hazardous Weather Outlook at:
https://www.weather.gov/erh/ghwo?wfo=lox

NWS LOX Office Area Forecast Discussion