Stevenson Ranch, California Weather Forecast Discussion

581
FXUS66 KLOX 121131
AFDLOX
Area Forecast Discussion...UPDATED
National Weather Service Los Angeles/Oxnard CA
431 AM PDT Fri Sep 12 2025
UPDATED AVIATION SECTION
.SYNOPSIS...12/333 AM.
A warming trend is on the way, with temperatures increasing a
couple degrees from day to day through next week. Night through
morning low clouds and fog will affect the coasts and coastal
valleys through next week. The heat peaks during the middle of
next week, and will be replaced by a slow cooling trend and
perhaps a few showers and thunderstorms by the end of next week.
&&
.SHORT TERM (TDY-SUN)...12/333 AM.
Upper heights are presently at their minimum, with a CONUS-full-
latitude trough over the western states. But change is on the way,
as the trough departs to the east and a ridge amplifies in its
wake. This will induce a warming trend beginning today. High
temperatures this afternoon will gain a couple degrees from
yesterday, reaching the mid 70s to mid 80s in most places, cooler
at the beaches. The day-to-day warming will be modest, however, as
periodically reinforcing troughs over the Pacific NW prevent more
substantial height rises from materializing across the local
area. Nevertheless, gradually weakening LAX-DAG onshore pressure
gradients beneath the initial boost in midlevel heights should
correspond to high temperatures rising a couple of degrees from
day to day. By Sunday, expect highs in the 80s in most places,
breaching 90 degrees in the typically-warmer interior valley
locales, but remaining in the 70s closer to the ocean. And with
the decreasing onshore pressure gradients and rising midlevel
heights, marine stratus and fog should clear more quickly during
the diurnal heating cycle -- progressively through the weekend --
but still return to the coasts and coastal valleys each night.
There will be a tendency for fog to increasingly predominate over
low clouds through the weekend, and there will be a 20% chance for
Dense Fog Advisories to become necessary during the night through
morning for this weekend. Precipitation will not occur through
the period.
Earlier Sundowner winds have weakened, and the Wind Advisory in
southwest Santa Barbara County has been cancelled. Additional weak
Sundowners are anticipated each late afternoon through early
overnight into this weekend, though peak gusts are presently
forecast to primarily range from 35-40 mph.
.LONG TERM (MON-THU)...12/333 AM.
The warming trend continues into next week, peaking around mid-
week. Heights at 500 mb are forecast to reach just short of
590 dam over Southern California on Tuesday and Wednesday. And
with pressure gradients continuing to trend less onshore from day
to day, high temperatures by Tuesday and Wednesday are projected
to reach well into the 90s in most places away from the ocean,
with 100-105F readings over some of the warmer valleys such as the
western San Fernando Valley. Also, the tendency for night through
morning fog -- potentially dense -- to be favored over low clouds
across the coasts and coastal valleys will continue, and there
will be a 20% chance for Dense Fog Advisories to be necessary next
week.
Also of note, monsoonal moisture is forecast to begin to re-enter
the area by the middle of next week, which could boost heat
indices, elevate overnight lows (readings not falling much below
70F in many areas), and favor dense fog near the coast. Regarding
heat impacts, currently next Wednesday appears to feature the
hottest temperatures, and there is a 30% chance for Heat
Advisories to become necessary in some areas on Wednesday -- given
high temperatures 10-15 degrees above normal away from the coast,
increased humidity, and limited relief from the heat with the
elevated overnight low temperatures.
Medium-range model guidance suggests that the aforementioned
monsoonal moisture appears to come from the phasing of a diffuse
and slow-moving upper low off the Southern California coast --
largely detached from steering currents aloft -- and a poleward
flux of subtropical moisture east of the upper low. There are a
lot of mesoscale factors that will greatly influence the impact of
this moisture on local-area sensible weather, especially given
the distant forecast-time range. However, an appreciable subset
of numerical model solutions suggest that this pattern will favor
shower and thunderstorm potential across the local area by next
Friday, and perhaps as early as Thursday. Given the westward-
displaced moisture plume directed by the flow around the offshore
upper low, shower and thunderstorm chances will be distributed
across most locations south of Point Conception including beaches,
coasts and valleys, and there could even be a nocturnal component
to this activity. And given the position of the upper low
offshore, even further increases in humidity and cloud coverage
are currently expected to yield a slow cooling trend by late next
week. Overall, this is a low-confidence forecast -- given low
predictability inherent to such small-scale forcing features at
this distant of a forecast-time range, though thunderstorm impacts
will be possible.
&&
.AVIATION...12/1122Z.
At 0651Z at KLAX, the marine layer depth was 1100 ft, with an
inversion topped at 1300 feet and 19 degrees C.
High confidence in TAFs for KPMD and KWJF.
Low to moderate confidence in all coastal and valley TAFs,
although marine layer clouds are beginning to fill in. Cigs may
frequently bounce between BKN and SCT IFR- MVFR through 18Z at any
coastal or valley site. There is a chance for low clouds to form
at KOXR (40%) and KCMA (20%) through 18Z. Minimum flight cat may
be off by 1 cat. Higher confidence in a more widespread marine
layer after 00Z Sat, but arrival times may be off +/- 3 hours.
KLAX...Moderate confidence in TAF. Cigs are likely to bounce
between BKN and SCT 010-025. There is a 20 percent chance of an
east wind component of 8 kt from 10Z-17Z Fri. Higher confidence in
BKN08-015 cigs after 02Z Sat, but arrival times may be off +/- 2
hours.
KBUR...Moderate confidence in TAF. Dissipation of cigs may be off
+/ 90 minutes. Cigs may frequently bounce from BKN to SCT. Arrival
of BKN005-012 cigs tonight may be off +/- 2 hours.
&&
.MARINE...12/250 AM.
Small Craft Advisory (SCA) level NW winds (peaking at 20-30 kts)
will impact the outer waters through Sunday night. Winds will be
the strongest during the afternoons and evenings, and lulls may
occur during the morning hours. The nearshore waters along the
Central Coast will see SCA level NW winds (20-30 kts) each
afternoon and evening through Sunday night. Seas will peak around
6 to 8 feet through late Sunday.
For the inner waters south of Point Conception, SCA level WNW
winds (20-25 kts) are likely across the Santa Barbara Channel
Friday, with moderate chances Saturday and Sunday, then conditions
will be below SCA levels into next week. Seas will be choppy and
peak at 3 to 5 feet this afternoon and evening. Some localized NW
gusts to 20 kts may occur near Point Dume and west of Catalina
this afternoon and evening, then winds will trend lighter over the
weekend and will be below SCA levels into next week.
&&
.LOX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...Small Craft Advisory in effect from 1 PM this afternoon to 9
      PM PDT this evening for zone 645. (See LAXMWWLOX).
     Small Craft Advisory in effect from 3 PM this afternoon to
      midnight PDT tonight for zone 650. (See LAXMWWLOX).
     Small Craft Advisory in effect until 3 AM PDT Saturday for
      zones 670-673-676. (See LAXMWWLOX).
&&
$$
PUBLIC...Cohen
AVIATION...Lewis
MARINE...Lewis
SYNOPSIS...Cohen
weather.gov/losangeles
Experimental Graphical Hazardous Weather Outlook at:
https://www.weather.gov/erh/ghwo?wfo=lox

NWS LOX Office Area Forecast Discussion