102
FXUS66 KLOX 011002
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
302 AM PDT Mon Jul 1 2024

.SYNOPSIS...30/219 PM.

A significant heatwave will impact a large part of the area this
week and continue into next weekend. Temperatures will become
dangerously hot across much of the area. High temperatures by mid
to late week are expected to reach 95 to 105 degrees in many areas
away from the coast, with highs upwards of 105 to 115 over
interior valleys and foothills including the Antelope Valley.
Also, by late week, very warm to hot conditions could extend
closer to the coast. Patchy night and morning dense fog will be
possible near the coast early this week.

&&

.SHORT TERM (TDY-WED)...01/244 AM.

The marine layer is 900 ft deep but is slowly rising as an eddy
spins and lifts the marine layer. By dawn low clouds should cover
almost all of the coasts and will extend into a few vlys notably
the San Gabriel and eastern San fernando. A weak trof will pass
over the area today will will further lift the clouds. Low clouds
will slowly dissipate this morning but with an 8 mb onshore push
to the east in the afternoon it is likely that a few west facing
beaches will not clear. The lower hgts from the trof and the
deeper marine layer will team up to knock 2 to 4 degrees off the
max temps. The coastal areas will end up a few degrees blo normal
while the rest of the area will see near normal temps.

After today the forecast will be all about the heat. The heat wave
will start Tuesday as a large and warm E Pac high begins to nose
into the state from the west. There will be marine layer clouds
across the coasts in the morning but there will be weaker onshore
flow so clearing should be a little faster and more beaches will
see sunshine. Max temps will rise 1 to 2 degrees across the coasts
and vlys except for the Central Coast where even weaker onshore
flow will allow for a 3 to 5 degree warm up.

The warm up will begin in earnest on Wednesday as the upper high
pushes further into the state and hgts rise to 595 dam over LA
county and 596 dam over the Central Coast. At the same time the
onshore flow will lessen which will lead to a later arriving and
weaker sea breeze. The marine layer will be squashed to under 1000
feet and likely lower to near 600 ft. This will lead to low clouds
only covering the near shore area in the morning. The capping
inversion will be very strong and this may prevent some beaches
from clearing. Max temps will rocket up 5 to 10 degrees
everywhere. There will many 80 degree reading across the interior
coast, lots of 90s and some 100 to 101 degree readings in the
vlys. The interior and lower mtn elevations will see max temps
ranging from 102 to 106 degrees. The Antelope Vly will have
dangerous heat with highs of 108 to 112 degrees.

The Excessive Heat Warning for interior areas starts on Tuesday
which may be a day early and the day shift will have to consider
pushing the start date back a day. There is no doubt about the
need for Warnings across the interior on Wednesday. In addition to
the warnings, an Excessive Heat Watch has is also in effect from
the San Fernando Valley through the Santa Monicas, Calabasas, and
Agoura Hills, to the central Ventura County valleys and through
the Santa Ynez Range and Santa Lucia Range.

Overnight lows will have to monitored as the areas in the warmest
portion of the inversion (likely 800 to 1500 ft elevations) may
not see much cooling relief at all in the overnight hours.

n addition, gusty west to northwest winds are expected each
afternoon over most of the interior areas. The strongest gusts
(35-45 mph) will occur over the I-5 corridor and the western
Antelope Valley/foothills. These gusts will come in just under
wind advisories criteria.

.LONG TERM (THU-SUN)...01/302 AM.

The heat wave will persist through the xtnd period and into early
next week. The upper high will move directly atop of the state and
Srn CA will have hgts near 596 dam overhead through the entire
period. The sfc gradients weaken considerably on Fri and Saturday
and these will be the warmest two days with only a minimal amount
of marine layer clouds or marine layer influence.

Look for 2 to 4 degrees of warming each day Thu and Fri and just a
little cooling over the weekend. The Excessive Heat Warnings and
Watches will continue all the way through the weekend and into
early Monday morning, July 8 with max temps of 95-105 degrees in
many areas away from the coast, with highs upwards of 105-115 over
interior valleys and foothills including the Antelope Valley.

With max temps 10 to 20 degrees above normal, Major to Extreme
heat risk is likely through the weekend, especially Friday.

Overnight low temperatures will be well above normal in the
inversion zone with lows remaining above 80 degrees at some
locations over interior valleys and nearby foothills. These warm
lows will worsen the effects of extreme heat.

Even though they are not included in the watch the interior
coastal sections may well need Heat Advisories during the period
as the marine layer shrinks until it is too shallow to provide
much relief to the portion of the coast not in the near shore
area.

One last area of concern is the SBA south coast where Sundowners
are possible Thursday and Friday nights. Warming downsloping
sundowner winds could easily bring near 100 degree temperatures to
the SBA south coast including the city of SBA during the early
evening hours.

The combination of these very hot temperatures, areas of low
humidities and possible sundowner winds will lead to fire weather
risks. Please see the fire weather discussion below for all the
details.

&&

.AVIATION...01/0625Z.

At 06Z at KLAX, the marine layer was 600 feet deep. The top of
the inversion was at 2300 feet with a temperature of 26 Celsius.

High confidence in VFR conditions for for KPRB, KWJF and KPMD
through at least Monday.

Moderate confidence in all airports that get ceilings seeing LIFR
conditions at times, low confidence on coverage and timing. VLIFR
dense FG possible anywhere, especially before 12Z. There is a
30-40 percent chance of improving flight categories after 10Z due
to an eddy focused across KLAX, KSMO, KLGB.

For KBUR and KVNY there is a 10-20 percent chance that the eddy
is strong enough for at least brief LIFR/VLIFR cigs/vsbys in the
10-15Z time frame.

KLAX...Low confidence in TAF with a moderate to strong eddy
providing a 30-40 percent chance of improving flight category
after 10Z. There is a 30 percent chance of a brief return to VFR
conds between 07Z-10Z. Return to VFR later this morning may be off
by 3 hours. High confidence in any easterly wind component
staying well below 06 knots. Note that the TAF will reflect vsby
on the ground, not at the tall tower at 300 ft agl.

KBUR...Moderate confidence in VFR conditions with a 10-20 percent
chance of LIFR cigs/vsbys between 10-15Z.

&&

.MARINE...01/235 AM.

For the Outer Waters, moderate to high confidence in current
forecast. Through Monday night, high confidence in Small Craft
Advisory (SCA) level winds from San Nicolas Island northward. For
the waters north of Point Conception (PZZ670/673), there is a
50-60% chance of Gale force winds through early this morning and
30-40% chance of Gale force winds Monday afternoon and Monday
night. The GALE WARNING for PZZ670/673 has been extended through 9
am this morning. For Tuesday through Friday, high confidence in
winds and seas remaining below SCA levels.

For the Inner Waters north of Point Sal, moderate confidence in
current forecast. There is a 40-60% chance of SCA level winds
through this evening. For Tuesday through Friday, high confidence
in winds and seas remaining below SCA levels.

For the Inner Waters south of Point Conception, there is a 30%
chance of SCA level winds this afternoon/evening but likely will
stay very localized. Otherwise, high confidence in winds and seas
remaining below SCA levels through Friday across the Inner Waters
south of Point Conception.

Patchy dense fog (with visibilities one nautical mile or less)
will continue to impact the coastal waters through the week. The
areal coverage of the dense fog will likely decrease each day.

&&

.FIRE WEATHER...30/429 PM.

Elevated fire weather conditions will continue across the
interior valleys, mountains, and deserts through Monday due to hot
temperatures, low humidities, and locally gusty onshore winds.

Beginning on Tuesday, and continuing into next weekend, high
pressure will build into the region from the Eastern Pacific. This
will likely bring a significant and long duration heat wave away
from the coast from Tuesday through next weekend. High
temperatures between 100 and 110 degrees will be common across the
interior during this period, with temperatures potentially rising
to between 110 and 115 degrees across the Antelope Valley and San
Luis Obispo County interior valleys during the peak of the heat
Thursday through Saturday. Overnight lows will also remain quite
warm, adding to the potential for dangerous heat mid to late week.
Widespread humidity values between 7 and 15 percent will likely
occur across the interior during this period, along with poor
humidity recoveries, especially in the mountains, foothills, and
Antelope Valley. Typical gusty onshore winds are expected across
interior sections in the afternoon and evening hours, with gusts
of 20 to 35 mph common. There is also the potential for gusty
sundowner/I5 corridor winds late Thursday into Friday night which
could bring hot and dry conditions into portions of southern Santa
Barbara county.

Given the very hot temperatures, low relative humidity, and
locally gusty winds, an extended period of elevated to brief
critical fire weather conditions are likely from Tuesday through
Sunday for valley, foothill, mountain, and desert locations.
Elevated to critical fire weather conditions may expand into
southern Santa Barbara county if the sundowner winds develop late
Thursday into Friday night. The hot and unstable conditions will
also increase the threat of large vertical plume growth for any
fires that develop across the interior. The very hot and dry
conditions will also cause a significant drop in both live and
dead fuel moisture levels this week. These drying fuels combined
with the expected fire weather conditions and increased outdoor
activities associated with the 4th of July will cause the large
fire threat to become high for areas away from the coast Tuesday
through next weekend.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Excessive Heat Warning remains in effect from 11 AM Tuesday
      to 5 AM PDT Monday for zones 38-343>345-353-376>379-381>383. (See LAXNPWLOX).
     Excessive Heat Watch remains in effect from Wednesday morning
      through late Sunday night for zones
      88-342-348-351-352-356>358-369>375-380. (See LAXNPWLOX).
PZ...Small Craft Advisory in effect until 9 PM PDT this evening
      for zone 645. (See LAXMWWLOX).
     Gale Warning in effect until 9 AM PDT this morning for zones
      670-673. (See LAXMWWLOX).
     Small Craft Advisory in effect until 3 AM PDT Tuesday for
      zone 676. (See LAXMWWLOX).

&&

$$

PUBLIC...Rorke
AVIATION...Munroe
MARINE...RM/RAT/RK
FIRE...Gomberg
SYNOPSIS...Cohen

weather.gov/losangeles

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