Monrovia, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

150
FXUS66 KLOX 150541
AFDLOX

Area Forecast Discussion...UPDATED
National Weather Service Los Angeles/Oxnard CA
941 PM PST Thu Nov 14 2024

.SYNOPSIS...14/908 PM.

A cold low pressure system will bring chances of rain to the area
this evening through Friday night. Temperatures will plummet to
around 10 degrees below normal by Friday, with gusty west to
northwest winds by the afternoon. A gradual warming trend is
expected Sunday into next week with moderate to strong Santa Ana
winds and low humidities returning Tuesday through Thursday.

&&

.SHORT TERM (THU-SUN)...14/909 PM.

***UPDATE***

High temperatures today for areas North of Point Conception
were generally in the 60s to 70 range, while areas South of Point
Conception were near mid 60s to mid 70s. Northwest to north wind
gusts of 30 to 45 mph, locally 50 mph are being reported across
the Santa Ynez Range and Santa Barbara South Coast thanks to an
-4 mb SBA to SMX gradient and -2 SBA to BFL gradient. No changes
 are needed to the current wind advisories in place, as winds are
 expected to continue across these areas into at least mid
 morning Friday.

The rest of the forecast overnight will be completely at the will
of the trough currently moving into the region. Lower level
clouds are rather patchy and erratic, scattering in and out,
mainly for areas north of Point of Conception. Meanwhile some mid
to high level clouds will start to nudge in overnight and further
disrupt the lower level clouds. Between the chaotic cloud
patterns, and the colder air moving into the region, wind-
sheltered and higher elevation areas are expected to fall into the
30s tonight, while the rest of the area are expected to be in the
mid 40s to low 50s. As of right now, no frost/freeze hazards are
in effect as the cloud cover may prevent radiative cooling, but it
is not out of the question that the overnight shift may need to
issue an advisory or two.

Forecast for tomorrow still looks on track, with a very light
sprinkle-y/shower-y precip pattern. More details about
accumulations can be found below in the previous discussion. High
temps Friday are expected to drop as much as 10 degrees across
the majority of areas north of Point Conceptions and the coasts to
the south. The high temps for the interior valleys and
mountains/foothills could see highs 10 to 20 degrees cooler than
today, with widespread temperatures in the 50s and 60s across the
region. For context, these temperatures will be 10 degrees below
normal for this time of year. Increasing northwest to north winds
look to still be on track for tomorrow, with gusts of 35 to 50 mph
possible across the mountains, deserts, and southern Santa
Barbara County. Have held off on issuing wind advisories for now,
as current guidance suggests that winds may not reach advisory
levels in any one location for long enough.

Otherwise forecast was in shape and no updates were needed at this
time.

***From Previous Discussion***

Really not much change to the forecast through Saturday as models
have remained more or less steady with the track and speed of the
low. While the system is quite cold for this time of year, noted
by the large area of open cell cumulus between 125-130w,
precipitable waters are under .5" so there isn`t much moisture
with this. And given the more inland trajectory, most areas south
of Pt Conception will be significantly rain-shadowed. Even going
with the high end 90th percentile precip forecast from the GEFS,
ENS, and GEPS, rain totals from this system are expected to be
under a quarter inch across for roughly 90% of the area (basically
just the Grapevine region and right around Pt Conception) and
under a tenth of an inch for about 75% of the area. Most of that
falling later tonight into Friday. So this won`t be a wetting rain
for most areas, and for the rain-shadowed areas south of Pt
Conception, roughly from Goleta to the western San Fernando
Valley, likely just a trace of rain or possibly as much as 0.02".

The cold air with this system is already helping to generate some
isolated lightning strikes a few hundred miles offshore. Not
expecting these to move onshore but could see a couple strikes
over the coastal waters mostly north of Pt Conception tonight into
Friday morning. In addition, gusty west to winds will develop as
early as Friday morning across the coastal waters and elsewhere
Friday afternoon, though strongest near the coast where wind
advisories may be needed.

Cool but dry Saturday with highs only in the lower to mid 60s at
lower elevations. Several degrees of warming expected Sunday with
clear skies and light offshore flow in place. Gusty north winds
expected across the Grapevine region Sunday night. EPS ensembles
indicating winds gusting to 50 mph in that area, some of which
will likely filter down into the valleys through Monday morning.

.LONG TERM (MON-THU)...14/218 PM.

Aside from some gusty north winds Monday morning across the
Grapevine region down through west LA, Monday should be a quiet
weather day. Slightly cooler most areas as onshore flow briefly
returns.

Offshore expected to return Tuesday through Thursday, though there
remains quite a bit of uncertainty on the strength. Deterministic
forecast gradients have been fluctuating quite a bit, lately
trending down, which seems more reasonable given the lack of upper
support. There are still some ensemble solutions supporting a
slower and more westward trough the Great Basin, though most of
the solutions are faster and warmer with more ridging over
California. Still very dry, likely even drier than the last
Santa Ana event, with some wind, but at this time leaning more
towards and advisory level event with gusts at or below 50 mph
through the usual Santa Ana wind corridor. Will see how the models
evolve over the next few days. Current temperature forecast is
straight from the NBM and seems several degrees too cool for mid
week. Local historical based guidance suggest high temperatures at
least in the upper 70s for coast/valleys and likely into the 80s.

&&

.AVIATION...15/0541Z.

At 0505Z at KLAX, there was no inversion.

There is a chance of showers through the period. VFR conditions
will periodically dip to MVFR at times ahead of a frontal system
moving over the area, and also near any showers that occur. Rain
chances are highest north of Point Conception through midnight,
especially over the interior mountain slopes, then spreading over
areas S of Pt. Conception around or after midnight.

KLAX...Moderate confidence in the 06Z TAF with VFR conds expected
through around 09Z. The arrival time of MVFR cigs could differ by
+/- 2 hours from the TAF time. There is a low chance of light
rain (10-15%) between 09Z to 16Z. No significant east wind
component is expected, but gusty west winds are expected starting
at 14Z, and especially by 18Z through 05Z Sat.

KBUR...Moderate confidence in the 00Z TAF with VFR conds expected
through much of the period, but with periodic MVFR CIGs. The
timing of MVFR CIGs and any rain showers is low confidence

&&

.MARINE...14/816 PM.

In the outer waters, winds and seas will remain at SCA levels
thru Sat evening, then will drop below SCA levels by late Sat
night. There is a 30% chance of Gale force winds Fri afternoon
into Fri night, mainly in PZZ676. There will likely be a break in
the SCA conds Sunday in the morning through afternoon hours. SCA
conds are then likely again (70-80% chance) Sun night thru Mon
night, except for through Tuesday morning in PZZ676 and 673. Large
seas of 10-14 feet are expected tonight through Saturday evening
but are likely to build again Monday through Tuesday.

For the inner waters N of Pt. Sal SCA conds will thru late Fri
night. Winds may drop below SCA levels for a few hours late
tonight and Fri morning. There is a 20% chance of SCA conds Sat
afternoon and evening, especially for Point San Luis. SCA conds
are not expected late Sat night thru Mon morning, then are likely
(60-70% chance) Mon afternoon/evening.

In the Santa Barbara Channel, a GALE warning has been issued, with
gusts to 35 knots in the mid to western channel, along with very
hazardous seas of 6 to 8 feet at 6 seconds. Winds may drop below
SCA levels for a few hours early Fri morning across the eastern
sections. SCA level winds are likely (60% chance) Sat
afternoon/eve. Winds and seas should be below SCA levels late Sat
night thru Mon morning, then are likely (60% chance) Mon
afternoon/eve, mainly western sections.

In the southern inner Waters, SCA level winds will continue thru
late Fri night. Winds may drop below SCA levels for a few hours
late tonight/Fri morning, especially in eastern sections. Winds
and seas should be below SCA levels late Sat eve thru Mon night.

Large, short period seas 5 to 8 feet are expected nearshore inside
the SOCal Bight through Fri night, and 8 to 10 feet across the
western portions.

&&

.BEACHES...14/220 PM.

Large W to NW swell will likely bring High Surf to Central Coast
beaches beginning this afternoon then continuing thru Sat
morning, with surf peaking late tonight/Fri. Surf heights of 9 to
13 ft are expected at the peak of the event, with local sets to
15 ft. Surf will be highest on exposed W and NW facing beaches.

High surf will likely affect the beaches of VTU County this
evening thru Sat morning. Surf is expected to peak at 6 to 8 ft
late tonight/Fri, with local sets to 10 ft possible. Elsewhere on
the beaches S of Pt. Conception, elevated surf is likely this
evening thru Sat morning, with surf heights of 3 to 6 ft and local
sets up to 7 ft. There is a chance that High Surf Advisories will
have to be expanded to the L.A. County Coast Fri into Sat.

Minor coastal flooding is possible on west and northwest-facing
beaches during the high tides Fri morning and Sat morning, with
nuisance coastal flooding possible on exposed west-facing beaches
south of Pt. Conception. High tides are between 800 AM and 830 AM
PST Friday morning, and 830 AM to 900 AM PST Sat morning.

&&

.FIRE WEATHER...14/523 PM.

***CRITICAL FIRE-WEATHER EVENT INCLUDING *** POTENTIAL HIGH-END
 RED FLAG*** CONDITIONS FROM A MODERATE TO POSSIBLY STRONG SANTA
 ANA WIND EVENT BECOMING LIKELY BETWEEN NEXT TUESDAY AND
 THURSDAY***

***FIRE-WEATHER HEADLINES LIKELY BETWEEN NEXT TUESDAY AND
 THURSDAY-- GREATER THAN 80 PERCENT CHANCE***

Between next Tuesday and Thursday, a moderate to possibly strong
Santa Ana wind event is likely to develop. This will bring an
increasing likelihood for critical fire-weather conditions
including ***POTENTIAL HIGH-END RED FLAG*** conditions.

At the synoptic scale, the key feature that we will be watching
is the proximity of the closed low that develops near the four
corners area and how quickly it ejects eastward. Current 12z
operational models are trending further east with this low,
which would likely result in less upper level wind support than
previous model runs. As a result, the Santa Ana wind event that
develops between and Thursday will likely be a moderate event.
However, there model ensemble solutions show around a 20 percent
chance of a strong Santa Ana wind event.

The next Tuesday through Thursday Santa Ana event will likely be
a warmer and drier Santa Ana wind event compared to the event from
last week. Relative humidities may be 5% drier over the coastal
slopes and valleys for next Tuesday through Thursday
-- with potential for widespread single digit relative humidities
at times -- as temperatures warm well into the 70s and 80s
(enhancing the fire-plume growth- potential component). Latest
LAX-Daggett offshore pressure gradients are projected to be in the
-5 to -6 mb range, somewhat weaker than previous model solutions.
The strongest winds will likely be focused in the typical Santa
Ana wind prone areas of western LA and eastern Ventura counties.

One notable difference between the next Tuesday through Thursday
event compared to the event from last week is that the stronger
upper support for next Tuesday through Thursday should be
displaced much farther east, owing to the synoptic-scale
interactions discussed above. As a result, present indications
are that winds will not be quite as extreme for next Tuesday
through Thursday (modestly reducing the extent of long-range
spotting potential). Nevertheless, moderate to possibly strong
Santa Ana winds are likely between Tuesday and Thursday, and there
is a greater than 80% chance that fire-weather headlines will
become necessary across much of Los Angeles and Ventura Counties
for Tuesday through Thursday of next week. With very poor overnight
relative humidity recovery expected, this will have the potential
to be a long- duration Red Flag event, adding to the potentially
very favorable fire-weather environment for large fire development.

Also of note, spotty elevated fire-weather conditions cannot be
ruled out over the interior mountains of Santa Barbara and San
Luis Obispo Counties next week, though the focus for stronger
winds will be in Los Angeles and Ventura Counties.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...High Surf Advisory in effect until noon PST Saturday for
      zones 340-346-354. (See LAXCFWLOX).
     Wind Advisory remains in effect until 10 AM PST Friday for
      zones 349-351-352. (See LAXNPWLOX).
PZ...Small Craft Advisory in effect until 3 AM PST Saturday for
      zones 645-655. (See LAXMWWLOX).
     Gale Warning in effect until 3 AM PST Friday for zone 650. (See LAXMWWLOX).
     Small Craft Advisory in effect until 3 AM PST Sunday for
      zones 670-673-676. (See LAXMWWLOX).

&&

$$

PUBLIC...MW/Lund
AVIATION...Smith
MARINE...RAT/Black/Smith
BEACHES...DB/Black
FIRE...Gomberg/Cohen
SYNOPSIS...MW/Lund

weather.gov/losangeles

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