Toluca Lake, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

748
FXUS66 KLOX 181417
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
617 AM PST Sat Jan 18 2025

.SYNOPSIS...18/500 AM.

Areas of low clouds this morning in most coastal and valley areas
will give way to mostly sunny skies today, but it will be cool.
Offshore flow will return Sunday, with local northeast breezes,
less morning low clouds, and a few degrees of warming. Mostly
clear and locally breezy conditions are expected Sun night and
early Monday, then Santa Ana winds will increase during the day.
A moderate to strong Santa Ana wind event will likely affect
Ventura and Los Angeles Counties Monday night and Tuesday, with
offshore flow continuing for much of next week. Temperatures will
likely be below normal Monday and Tuesday, with a warming trend
later next week. Humidities will be low to very low all most of
next week. Frost or freezing temperatures are possible in wind
sheltered areas each night Monday night through Thursday night.

&&

.SHORT TERM (TDY-MON)...18/559 AM.

The marine layer across the region was fairly deep this morning,
generally around 3000 ft deep or so. N of Pt. Conception, low
clouds were widespread in coastal and valley areas, and have
pushed into the interior valleys and mtns of SLO County. S of Pt.
Conception, clouds were widespread in coastal and valley areas of
L.A. County and the valleys of VTU County, and have pushed into
the coastal slopes of the San Gabriel mountains.

The stratus field was more solid in nature this morning. However
W-E onshore pressure gradients between KLAX and KDAG have begun to
weaken, and N-S gradients between KSBA and KSMX, and KSBA and
KBFL have flipped offshore. Likely due to the gradients, clouds
have backed out of the Santa Clarita Valley during the past hour
or two, and it remained mostly clear in coastal sections of VTU
County and on the south coast of SBA County. However, it is
possible that some clouds may drift into these areas by daybreak.

Skies should clear in most areas by late morning. Small height
rises, a degree or two of warming at 950 mb and weakening onshore
gradients may allow for a couple of degrees of warming in most
areas, but max temps will still be several degrees below normal.

The upper high in the eastern Pacific will amplify a bit tonight
and Sun, and the upper flow will veer to a more northwesterly
direction. N-S gradients will remain weakly offshore, while W-E
gradients between KLAX and KDAG will become 3 to 4 mb offshore.
There may be some gusty NW-N winds through the I-5 Corridor and
across southwestern SBA County this evening into tonight, then
some NE breezes are possible in the mtns and locally in the
valleys of L.A./VTU Counties late tonight/Sun morning. With
minimal upper level support, expect any winds to remain well below
advisory levels.

Low clouds tonight/Sun morning will likely be limited to south
coastal sections of L.A. County and perhaps the Central Coast.
Where skies remain clear and winds remain light, it will be quite
chilly tonight, with frost likely in clear portions of the
Central Coast, and in portions of the valleys of VTU County and
western L.A. County. Any low clouds should clear by mid morning
Sun. Max temps should be up a few degrees in most areas Sun,
possibly reaching 70 degrees in the warmest valley locations of
L.A./VTU Counties, about normal for the second half of January.

The upper ridge off the West Coast will amplify Sun night and
Mon, with ridging extending all the way into central and northern
British Columbia. This will send a rather strong short wave
southward through the western states, resulting in a positively-
tilted trough over Arizona and far eastern California. This will
produce an increasingly sharp height gradient over the region by
Mon, with increasing northerly flow aloft. At the surface, N-S
offshore gradients will sharpen Sun night and Mon morning. This
should bring some gusty NW to N winds to the Interstate 5 Corridor
and to southern SBA County Sun night, possibly close to advisory
levels, but most likely below. W-E offshore gradients will actually
weaken Sun night, before becoming more strongly offshore during
the day Mon. Low clouds should be minimal Sun night/Mon morning,
any form, will likely be confined to southern L.A. County and
southern portions of the Central Coast and Santa Ynez Valley.

W-E offshore gradients will increase during the day Mon, bucking
the typical diurnal trend, as cold advection and subsidence spill
southwestward into the area. The beginning of the cold advection
on Mon will likely lead to cooling in the mtns and the Antelope
Valley, while developing N to NE downslope winds will offset
cooling west and south of the mountains, leading to mostly minor
change in max temps, and perhaps some warming near the coast.

.LONG TERM (TUE-FRI)...18/606 AM.

A moderate to strong Santa Ana wind event will likely develop
fairly rapidly late Mon and Mon night, as strong cold air
advection and subsidence overspread the region once the axis of
the positively tilted trough pushes south and east of the area.

Cold air advection will be particularly strong, with temps at 850
mb plunging from 3C to -6C in the Antelope Valley in 12 hours
from late Mon afternoon (00Z Tue) and early Tue morning (12Z
Tue). The thermal gradient across L.A. County will be very sharp
by 12Z Tue, with 850 mb temps lowering from -6C in the foothills
of the Antelope Valley to about 11C in the San Fernando Valley, a
difference of 17C in about 20 miles as the crow flies. Not
surprisingly, strong subsidence or sinking air is expected during
this time. Offshore gradients between KLAX and KDAG are forecast
by the WRF to peak at -11 to -12 mb Tue morning. Even if that is
overdone by a couple of mb which is quite likely, gradients would
still be near -9 mb. The GFS and EC both show surface gradients
of about -7.5 mb between KLAX and KDAG Tue morning.

While confidence in a moderate to strong Santa Ana wind event is
growing, the exact magnitude of the strength of the peak winds is
still uncertain, as is whether or not there will be some mountain
wave activity, forcing winds into the foothills of the San
Gabriel Valley. With this event, winds are not especially powerful
from 700 mb and above to 500 mb, which may limit the threat of
mountain wave activity. However, cold air advection is especially
strong with this event, thanks to the very cold origin of the air
mass in Central Canada. At this point, it looks as though High
Wind Warning level gusts to 60 to 70 mph are likely in the San
Gabriel Mountains, the Santa Susana mountains, and the Santa
Clarita Valley Mon evening into Tue morning, with a good chance of
warning level winds in the northern San Fernando Valley, the
VTU County valleys, and at least the Western Santa Monicas. There
is at least 20-30% chance of warning levels winds in the foothills
of the San Gabriel Valley and possibly in the SGV itself.

Since this event has just entered the time window covered
by the high res models, have decided not to issue a High Wind
Watch at this time, though one will likely be issued later today
if future runs show the same scenario. Wind Advisories will likely
be needed in many parts of L.A./VTU Counties not covered by any
High Wind Watch. Skies will be clear Mon night/Tue. Max temps will
likely be down a few degrees Tue, even west of the mountains where
downsloping will not be enough to overcome the cold advection.
The best cooling will be in the mtns and the Antelope Valley.

All models show weakening offshore gradients Tue night and Wed.
though moderate gradients will persist into Fri, likely along
with advisory level winds at times. As if stuck in a nightmare
version of the movie Groundhog Day, yet another short wave
dropping southward into the Great Basin may bring another uptick
in northeast winds later Thu into early Fri as offshore surface
gradients increase, as does upper support.

Max temps will be below normal Tue, then a warming trend is likely
during the daytime Wed and Thu as heights rise. This extended
period of gusty offshore winds, unfortunately will be accompanied
by very low relative humidities from late Mon thru at least Thu.
Humidities may drop below 5 percent at times in the drier
locations Mon afternoon thru Tue evening, and a Fire Weather
Watch is in effect during that time. Very low humidity values will
likely persist into Thu or Fri. Where winds drop off at night, it
will be very chilly thanks to clear skies and bone-dry conditions,
with freezing temps possible in coastal sections of SLO and SBA
Counties, and in any wind-sheltered valleys of VTU/L.A. Counties.

There are increasing signals for some rain next weekend but so
far it is not looking like an atmospheric river. Both the EC and
GFS deterministic solutions are definitely not an AR pattern with
little to no tap of moisture to the southwest. And all but a few
of the 100+ ensemble solutions indicate rain totals under a half
inch. However, it will be very cold aloft, with temps near
-30C at 500 mb, raising the possibility of convective activity.

&&

.AVIATION...18/1333Z.

At 12Z at KLAX, there was no marine layer nor inversion.

Overall, moderate confidence in 12Z TAF Package. Timing of flight
cat changes may be off +/- 2 hours with minimum flight cats off
by +/- 1. There is a 30% chance of LIFR or even VLIFR conds at
KSMX from 06Z to 12Z Sun. Similar chances for MVFR conds at KSMO
and IFR conds at KLGB from 06Z to 12Z Sun.

KLAX...Moderate confidence in 12Z TAF. Timing of flight cat
changes may be off by up to +/- 2 hours. There is a slight chance
for 380. (See LAXRFWLOX).
PZ...NONE.

&&

$$

PUBLIC...DB
AVIATION...Black
MARINE...Black
SYNOPSIS...DB

weather.gov/losangeles

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