Monrovia, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

243
FXUS66 KLOX 111014
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
314 AM PDT Mon Aug 11 2025

.SYNOPSIS...11/311 AM.

High pressure aloft lingering across the region will keep a hot
weather pattern across many valley, mountain, and desert
locations into Tuesday. With exception along the coast where
persistent onshore flow and a marine layer will keep temperatures
cooler, temperatures will remain above seasonal normals through
midweek. Areas of night through morning low clouds and fog will
continue along the coast and into some coastal valleys through the
period. A cooling trend will develop between Wednesday and
Saturday as an upper-level trough approaches the West Coast.

&&

.SHORT TERM (TDY-WED)...11/313 AM.

The latest water vapor imagery shows a large upper-level ridge of
high pressure over the eastern Pacific Ocean and West Coast and
extending to a secondary ridge circulation over the Central Valley
this morning. Mostly clear skies prevail across the region this
morning, minus the typical night through morning low clouds and
fog. North of Point Conception, the low cloud field remains well-
entrenched, but south of Point Conception, low clouds are starting
to look problematic early this morning. Southwest flow aloft is
starting to break down as the ridge circulation to the north will
likely shift the flow to light southeasterly. This could end up
playing tricks on the marine intrusion, setting up a warmer day
across the Southland. An early morning update could be needed due
to the low clouds not materializing and temperatures needing to
be upped by a few degrees, but the forecast will wait to see if
the marine layer deck gets its act together.

Away from the coast into the valleys, mountain, and desert, a very
warm to hot air mass will continue. The air mass will turn much
hotter as one moves away from the coast, approaching or reaching
dangerously hot levels across the interior portions of the area
over the next couple of days. An extreme heat warning remains in
effect for the Antelope Valley and the adjacent foothills through
Tuesday evening, but a heat advisory was extended into Tuesday
evening for the Cuyama Valley and the Transverse Ranges away from
the coast. The secondary ridge center will linger across the
region into Tuesday and keep a light southeast flow aloft in
place, which should drive up heat risk parameters.

With the southeast flow aloft, a few clouds could develop over
the mountains this afternoon and evening, but the better chance
looks to be on Tuesday afternoon and evening when 850-500 mb
mixing ratios are progged to be the highest. Precipitable water
values do creep up above normal on Tuesday at KPMD, but the
residence time may not be long enough to develop any convective
storms.

A northwesterly surface pressure gradient will begin to tighten
over the coming days and gusty Sundowner winds will likely develop
each afternoon and evening through the week. NAM BUFR time height
sections for Gaviota suggest advisory level winds developing each
evening through Wednesday, while EPS ensemble members indicate a
period of higher wind gusts near advisory levels at KSDB. This
provides some confidence for a strengthening northwest gradient
throughout the week. Advisory level winds are likely to develop
each evening through Wednesday across southern Santa Barbara
County. A wind advisory was added for the southwestern portion for
this evening into late tonight, but future shifts may need to
extend or reissue these advisories. Winds through the Interstate 5
Corridor continue to look on the marginal side. The latest
forecast guidance agree with EPS ensemble wind gusts in keeping
the site just shy of advisory criteria.

A cooling trend will begin on Wednesday as an upper-level trough
replaces the ridge over the West Coast. Onshore flow should
strengthen through the remainder of the week. GEFS ensemble based
pressure gradients indicate strengthening KLAX-KDAG and KSMX-KBFL
through the week.

.LONG TERM (THU-SUN)...11/306 AM.

All frames of the WPC cluster analysis suggest a sharpening trough
along the West Coast through next weekend. GEFS and EPS 500 mb
height means fall from Tuesday through the weekend, indicating
troughing developing. This agrees well with the previously stated
GEFS ensemble members highlighting onshore flow strengthening
through the week. A cooling trend with a deepening marine layer
depth should be expected for the latter half of the week. EPS
cloud cover means all shows low clouds and fog returning to most
coastal locales through the week, potentially covering more of
the valleys toward the end of the week.

A tighter northwest surface pressure gradient will likely linger
into late week and keep gusty Sundowner winds in the forecast. ECMWF
EFI wind parameters are highlighting the period between Thursday
and Friday as being windier than the CFSR period across the
region and into the Santa Barbara Channel. This seems to line up
well with EPS ensemble wind gust means increasing for KNSI on
Thursday and Friday and add confidence to the strengthen northwest
gradient.

&&

.AVIATION...11/0648Z.

At 2243Z at KLAX, the marine layer was around 800 ft deep. The
top of the inversion was around 3600 ft with a temp of 29 C.

High confidence in VFR TAFs at KPRB, KBUR, KVNY, KPMD, and KWJF.
Smoke from nearby wildfires may cause reduced vis at times,
especially for KSBP, KSBA, and KPRB.

High confidence in cigs returning to all coastal sites, but timing
of flight cat changes could be off by +/- 3 hours and minimum
flight cat may be off by one cat at times. Vsbys <1SM are possible
at coastal sites north of Los Angeles County. There is a 40%
chance KOXR clears between 18Z and 23Z.

KLAX...Moderate confidence in TAF. Minimum cig height may be off
+/- 200 ft, and clearing time may be between 16Z and 19Z. Return
of low clouds could occur as early as 01Z Monday or as late as
07Z Mon. Any east wind component should remain below 7 kts.

KBUR...High confidence in  TAF. There is a less than 10% chance
for LIFR to IFR vsbys/cigs between 12Z and 17Z, but confidence in
potential min flight cat is low.

&&

.MARINE...11/226 AM.

For the outer waters, moderate to high confidence in the current
forecast. In the northern zone (PZZ670), there is a 50-60% chance
of SCA level wind gusts during the afternoon and evening hours
each day. For the outer waters south of Point Sal, there is a
50-60% chance of SCA wind gusts through Friday night, with brief
lulls possible during the late night through morning hours.

For the inner waters north of Point Sal, moderate confidence in
the current forecast with a 50% chance of SCA level winds during
the afternoon and evening hours today. Additionally, there is a
30% chance of SCA level winds during the afternoon and evening
hours on Tuesday, Thursday, and Friday. Otherwise, wind and seas
expected to remain below SCA levels through Friday night.

For the inner waters south of Point Conception, moderate
confidence in forecast. Across the SBA Channel, there is a 30-50%
chance of SCA wind gusts at at times, mainly during the afternoon
and evening hours through Friday especially across the western
portion. Otherwise,e conds are expected to be below SCA levels
through Friday night.

In addition, night to morning dense fog may continue at times
into early this coming week.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Heat Advisory remains in effect until 9 PM PDT Tuesday for
      zones 38-351>353-376>380. (See LAXNPWLOX).
     Wind Advisory in effect from 6 PM this evening to 3 AM PDT
      Tuesday for zones 349-351. (See LAXNPWLOX).
     Beach Hazards Statement in effect through Wednesday evening
      for zones 354-362-366. (See LAXCFWLOX).
     Extreme Heat Warning in effect until 9 PM PDT Tuesday for
      zones 381>383. (See LAXNPWLOX).
PZ...Small Craft Advisory in effect from noon today 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 from noon today to 3 AM PDT
      Tuesday for zone 670. (See LAXMWWLOX).
     Small Craft Advisory in effect until 3 AM PDT Wednesday for
      zones 673-676. (See LAXMWWLOX).

&&

$$

PUBLIC...Hall
AVIATION...Lund
MARINE...Ciliberti/Lewis/Lund
SYNOPSIS...Hall

weather.gov/losangeles

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