Simi Valley, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

691
FXUS66 KLOX 220505
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
905 PM PST Sat Dec 21 2024

.SYNOPSIS...21/706 PM.

A significant high surf event with coastal flooding is expected
this weekend into the upcoming week, with the most dangerous
conditions expected Monday and Tuesday. Patchy fog near the coast
will create low visibilities at times through Monday. Aside from
a small chance for light rain near the San Luis Obispo County
coast this weekend, it will be dry through Monday. A stronger
weather system could bring light rainfall to more areas Tuesday
and Tuesday night. Temperatures will range from near normal near
the coast, to well above normal for interior areas.

&&

.SHORT TERM (SAT-TUE)...21/904 PM.

***UPDATE***

Temperatures today trended cooler over many areas, but coastal
zones saw a slight warm up with faster clearing of marine layer
clouds. A cold front to the north brought additional clouds to San
Luis Obispo County, limiting high temperatures to the upper
50s-60s. Looking into tonight, another cold front is forecast to
pass to our north as high pressure clings onto the region.
As a result, additional clouds are expected tonight into Sunday
and possibly some very light rain for far northwestern portions of
San Luis Obispo County. Patchy fog will be possible for the
coasts and coastal plains, and may be dense at times near the
Ventura and LA County coasts. Conditions look rather benign into
Monday as gradients remain quite weak. Current forecast looks
pretty on track with only minor changes needed.

***From Previous Discussion***

***Significant high-surf event with coastal flooding this weekend
 into the upcoming week***

Another day of cooling temperatures across the valleys as a return
to onshore flow has pushed more cool ocean air inland. Meanwhile,
an earlier burn off of the low clouds and dense fog allowed
coastal areas to bounce back from the the mid to high 50s that
were prevalent there yesterday.

High cloud coverage will be increasing through the night and into
Sunday as lots of high level moisture pours in from a low
pressure system moving into the eastern Pacific. Sky coverage
will vary from mostly to partly cloudy and this will likely wreck
havoc on the stratus and fog coverage. Still, given the time of
year and the still fairly light gradients, areas of dense fog are
possible, more so south of Pt Conception than north. With the
moisture moving east of the area Monday night and still light
onshore flow, dense fog may be more prevalent than tonight.

Otherwise, pretty low impact weather through early next week. The
tail end of a weak system will may bring some very light rain to
northwest SLO County tonight into Sunday morning. Coast and
valley temperatures will warm slightly through Monday before
crashing again with the next system on Tuesday. Models have
consistently been showing this one having a slightly farther south
trajectory to it, giving it a better chance for dropping some
light rain even through Ventura and LA Counties Tuesday afternoon
and evening. Rain amounts are expected to be a half to one inch
across coastal SLO county, then dropping off quickly to a quarter
inch or less in Santa Barbara County and a tenth of an inch or
less elsewhere.

Please reference the High Surf Warning and High Surf Advisory, as
well as the Coastal Flood Advisory, regarding the significant
high-surf event.

.LONG TERM (WED-SAT)...21/151 PM.

Following the Tuesday system moderate to locally strong northerly
flow will settle in across the area with gusty winds particularly
in the mountains. Deterministic runs are showing gradients from
the north between 5 and 7mb consistently through the rest of next
week. Christmas day will be sunny but on the cooler side after
the trough passage with some gusty winds through the mountains and
canyons, including the Santa Ynez Range. Periods of gusty winds
will continue all week with a slow warming trend going into next
weekend. Longer range ensembles show very little in terms of
precipitation chances through the first week in 2025. Possibly a
couple weak systems for the Central Coast next weekend and early
the following week but these show little hope of bringing any
meaningful rain.

&&

.AVIATION...22/0003Z.

At 23Z at KLAX, the marine layer was 400 ft deep. The top of the
inversion was at 2200 ft with a temperature of 18 C.

Overall, moderate confidence in 00Z TAF Package. High confidence
for desert sites and KSBA, KBUR, KVNY. Moderate to Low confidence
for remaining sites.

After 06Z, there is a 20 to 30% chance of LIFR conds at cig/vsby
restricted sites. There is a 10 to 20% chance for VLIFR conds
after 10z.

Timing of Cigs/vsby restrictions may be off +/- 2 hours. Flight
cats could be off one or two, especially during worst conditions.

KLAX...Low confidence in 00Z TAF. VLIFR to IFR conds should
persist through 18Z-19Z then improve to MVFR. There is a 30%
chance for vsbys less than 1/2SM and cigs VV001-VV002 after 07Z.
Low confidence in the minimum flight cats after 00Z Monday till
the end of the fcst pd. No significant east wind component
expected.

KBUR...High confidence in 00Z TAF.

&&

.MARINE...21/831 PM.

Buoy observations indicate that seas are building on schedule with
high confidence that these large, long period west to northwest
swells will last through next week. Seas will peak at 15 to 20
feet across our Outer Waters, with the largest swells in our
Northern Waters. For our Inner waters, seas will peak around 12
feet for the Santa Barbara Channel and the waters west of Catalina
Island bordering PZZ676.

Between the Peaks, small craft advisory (SCA) seas will likely
persist (70-80% chance) widespread across much of our Outer
Waters through next week. These conditions pose a risk for
damaging breaking waves at Morro Bay and Ventura Harbor
entrances.

Alongside high seas, there is roughly a 70% chance of SCA level
winds for the waters around the Channel Islands beginning tomorrow
morning and persisting through at least Monday evening. By
Christmas Eve (Tuesday), we can expect SCA level winds to become
widespread across most of the coastal waters through at least
Thursday morning (80-90% chance). There is a 20% chance of GALE
force Gusts from around Point Conception south to San Nicolas
Island Wednesday morning into Thursday.

&&

.BEACHES...21/133 PM.

A large and long period west to northwest swell will bring
dangerously high surf, especially to west and northwest facing
beaches, of 18 to 25 feet to the Central Coast and 12 to 18 feet
to Ventura County during peak periods Monday through Tuesday. LA
and Santa Barbara Counties will see 8 to 12 foot surf Monday and
Tuesday. Otherwise, from this afternoon through most of next week,
advisory level surf can be expected and minor to moderate coastal
flooding is possible. Please reference our SRF and CFW products
for more details.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...High Surf Advisory in effect until 4 AM PST Wednesday for
      zones 87-349-350-362-366. (See LAXCFWLOX).
     High Surf Advisory in effect until 1 AM PST Sunday for zones
      340-346-354. (See LAXCFWLOX).
     High Surf Warning in effect from 1 AM Sunday to noon PST
      Tuesday for zones 340-346-354. (See LAXCFWLOX).
     Coastal Flood Advisory in effect from 2 AM Sunday to 9 AM PST
      Tuesday for zones 340-346-354. (See LAXCFWLOX).
PZ...Small Craft Advisory in effect until 2 AM PST Thursday for
      zones 645-670-673-676. (See LAXMWWLOX).
     Small Craft Advisory in effect until 4 AM PST Monday for zone
      650. (See LAXMWWLOX).

&&

$$

PUBLIC...MW/Phillips
AVIATION...Black
MARINE...Black
BEACHES...Lewis
SYNOPSIS...Phillips/MW

weather.gov/losangeles

Experimental Graphical Hazardous Weather Outlook at:
https://www.weather.gov/erh/ghwo?wfo=lox