Simi Valley, California Weather Forecast Discussion

382
FXUS66 KLOX 150329
AFDLOX
Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
829 PM PDT Sun Sep 14 2025
.SYNOPSIS...14/736 PM.
High pressure aloft will continue a warming trend through at
at least Tuesday. Areas of night through morning low clouds and
fog will continue for many coast and coastal valley areas through
Tuesday. Monsoonal moisture will spread over the area between
Tuesday and Wednesday and bring the possibility of showers and
thunderstorms for the mid-to- late week. A very warm and humid
air mass is likely to settle into the region during this period.
&&
.SHORT TERM (SUN-WED)...14/753 PM.
***UPDATE***
A strengthening upper level high centered over northern Mexico
will expand NWWD into southern California over the next several
days, causing a warming trend that will persist through Wednesday.
At the same time, monsoonal moisture will begin to spread over the
area from the south on Tuesday and continue through late week,
and possibly through the weekend. Highs on Monday are expected to
be in the 80s and 90s away from the coast and with 70s along the
beaches. Further warming is expected through Wednesday.
A deep marine layer combined with a coastal eddy over the San
Pedro Channel will spread low clouds well inland overnight tonight
into early Monday. There will be low clouds and fog over most of
the coast and coastal valleys by Monday morning with good clearing
expected in the afternoon. After this, the marine layer will begin
to shrink with low clouds being confined closer to the coast
Monday night into Tuesday.
Finally, there are gusty northerly winds affecting southwest Santa
Barbara County, including the western South Coast and Santa Ynez
Range. Gusts should be between 30 to 35 mph through late this
evening, shifting to the east to southeast and weakening
overnight.
***From Previous Discussion***
A quiet weather pattern will continue through Tuesday with the
biggest impact being the increasing heat across the area. Building
high pressure over the next 24 to 48 hours will warm up
temperatures several degrees, especially inland. Based on the
current forecast it`s a very borderline heat advisory situation
for parts of LA county Tuesday and Wednesday, but with the big
caveat being the increasing chances for showers and thunderstorms
Wednesday and beyond as the remnants of newly crowned Tropical
Storm Mario move north into our area. The added moisture aloft and
potential clouds and showers on Wednesday significantly complicates
the heat advisory chances so will have to take it day by day and
see how the pattern evolves. Will re-evaluate the heat advisory
potential on Monday. At the very least it will become increasingly
muggy Tuesday and especially Wednesday as PW`s increase to
between 1.5 and 2" which would be above the 95th percentile
climatologically.
Considering that Mario has only come into being over the last
several hours, there still remains quite a bit of uncertainty
where the remnants will track. The NAM and GFS continue to exhibit
fairly large discrepancies in timing and location and even amongst
the ensembles there`s a big disparity. A majority of the solutions
keep the bulk of the strongest activity offshore over the coastal
waters, and moving north towards the Bay Area, which would likely
favor the western portion of the area and not as much over LA
County. The NAM is quite a bit faster with it, showing possible
convection beginning as early as Tuesday afternoon across southern
areas and the adjacent coastal waters. However, most of the
ensembles suggest either late Tuesday night or Wednesday for the
onset of any convective activity south of Pt Conception and later
Wednesday into Thursday to the north. There could be a period of
dry lightning early on the in the event, but increasing PW`s
thereafter will keep most of the storms on the wet side. Also,
shower and thunderstorm activity could occur day or night as there
is ample instability aloft to generate storms even without the
sun`s heat. Flash flood potential will be increasing with time,
but the best chances for that would likely be Wed night into Thu
when the deepest moisture arrives.
.LONG TERM (THU-SUN)...14/217 PM.
Late Wednesday night into Thursday could be the period of
strongest and most widespread storm activity based on the
latest ensemble solutions. As mentioned, the current track appears
to favor the western portion of the area more than the east, but
certainly can`t rule out strong storms with heavy rain and
lightning anywhere.
After the initial surge of Mario moisture moves through Wednesday
and Thursday, models show a second moisture surge coming through
Friday into Saturday, maintaining shower and storm chances into
next weekend. So this could be a lengthy period of showery weather
with on and off thunderstorms with heavy rain at times and gusty
winds.
It will be warm and muggy through next weekend, even overnight as
well with clouds and moisture trapping a lot of the warmth from
the day. Widespread lows in the 70s are possible through next
weekend. Highs each day will be tricky and largely dependent upon
where the clouds and showers develop but will generally range
from the upper 70s to lower 90s. Given the higher than normal
humidities, can`t rule out the possibility of additional heat
advisories through the rest of the week.
&&
.AVIATION...15/0252Z.
At 0011Z at KLAX, the marine layer was 1200 ft deep. The top of
the inversion was at 2100 ft with a temperature of 27 C.
High confidence in KPMD and KWJF TAFs.
Low to moderate confidence for coastal & valley sites.
Timing of CIG/VSBY restrictions may be off by 3 hours & flight
categories may be off by one cat at times when CIGs are present.
There is a 30% chance LIFR CIGs arrive at least briefly at KSBP
from 12Z to 17Z Sunday. Similar chance that clouds do not arrive
at KPRB & KSMX. There is a 20% chance clouds do not arrive at KBUR
& KVNY.
KLAX...Moderate confidence in TAF. Arrival and clearing times may
be off by 2 hours. Flight minimums may be off by one category.
There is a 20% chance that there is and VFR transition through the
period or is very brief. No significant east wind component
expected through the period.
KBUR...Moderate confidence in TAF. Arrival and clearing times may
be off by 2 hours. 15% chance for LIFR cigs from 10Z to 15Z Mon.
20% chance for no low clouds tonight.
&&
.MARINE...14/805 PM.
Sub-tropical moisture will move northward into the coastal waters
this week, bringing chances of showers and thunderstorms to the
area as early as Tuesday, with better chances Wednesday through at
least Friday. Any thunderstorm that forms may create localized
dangerous ocean conditions with choppy seas, gusty erratic winds,
and/or frequent dangerous cloud to surface lightning. Boaters
should closely monitor weather conditions and avoid traveling near
showers and thunderstorms.
Small Craft Advisory (SCA) level NW winds (20-30 kts) will impact
the outer waters and the nearshore waters along the Central Coast
through early Monday morning, with seas peaking at 7-9 feet
across the northern waters. Then, conditions are expected to
weaken and remain below advisory levels on Monday and Tuesday.
Low to moderate confidence in winds increasing close to SCA levels
Wednesday through Friday.
For the inner waters south of Point Conception, conditions are
generally expected to remain sub-advisory through Tuesday morning.
There is a 25% chance for WNW winds of 20-25 kts (SCA levels) across
the Southern California Bight in the afternoon and evening on
Tuesday, increasing to 50% chance Wednesday.
&&
.LOX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...Small Craft Advisory in effect until 9 PM PDT this evening
      for zone 645. (See LAXMWWLOX).
     Small Craft Advisory in effect until 9 AM PDT Monday for
      zones 670-673. (See LAXMWWLOX).
     Small Craft Advisory in effect until 3 AM PDT Monday for zone
      676. (See LAXMWWLOX).
&&
$$
PUBLIC...MW
AVIATION...Black/Lund
MARINE...Black/Lewis/Lund
SYNOPSIS...MW/Hall/CC
weather.gov/losangeles
Experimental Graphical Hazardous Weather Outlook at:
https://www.weather.gov/erh/ghwo?wfo=lox

NWS LOX Office Area Forecast Discussion