498
FXUS66 KLOX 130715
AFDLOX

Area Forecast Discussion...UPDATED
National Weather Service Los Angeles/Oxnard CA
1215 AM PDT Sat Jul 13 2024

.SYNOPSIS...12/109 PM.

The long-lasting heatwave will continue across the mountains and
interior areas through Saturday as high pressure remains anchored
over the region. The high will weaken over the weekend into early
next week, causing a gradual cooling trend through the middle of
next week. In the meantime, temperatures inland will remain above
normal. Another warming trend will develop later next week and
continue into next weekend.

&&

.SHORT TERM (SAT-TUE)...12/835 PM.

***UPDATE***

There was a strong and low marine inversion early this evening
at around 900 ft deep. Low clouds were extensive along the coast
and will push inland overnight and into some of the adjacent
vlys. Patchy dense fog was noted along the Central Coast already,
with patchy dense fog not out of the question developing for some
coastal areas S of Point Conception overnight especially along the
SBA County S coast.

Otherwise and elsewhere, partly to mostly cloudy skies overall can
be expected as more mid-level moisture moves into the area from
the SE. There will also be a small chance (less than 15%) of
widely scattered showers and a 5-10% chance of a thunderstorm. The
chances of these are low enough to not be reflected in the
forecast. However, the NAM continued to show the possibility of
showers with a slight chance of thunderstorms all day Sat into
Sat evening especially for interior areas. Have updated the zones
to reflect this change. Any thunderstorms that develop would be
capable of producing brief heavy rain, isolated to widely
scattered dry lightning and strong, gusty and erratic winds.

Gusty SW-NW winds 15 to 25 mph with some gusts up to 30 mph will
persist this evening for the foothills, mtns and across the Antelope
Vly, but will diminish overnight.

It will be warm again tonight for the foothills, lower mtns and
deserts, with lows in the 70s to lower 80s expected. These warm
overnight lows will give little relief to the ongoing heat wave
for interior areas.

***From Previous Discussion***

Strengthening onshore flow along with a deeper marine layer are
helping to bring cooler temperatures to inland areas today. The
marine layer jumped up to 2000 feet across LA County sloping to
around 1500 feet along the Central Coast. Probably won`t see too
much change in the marine layer depth tonight an Saturday but the
inland cooling will continue as the upper high weakens and the
lower levels cool. Ironically, we may see a slight bump in
coast/valley temperatures over the weekend as onshore flow weakens
by 2-3mb. The temperature rises won`t be excessive and should not
jump into the advisory/warning level. The one caveat there is the
models are indicating increasing moisture aloft with the southeast
flow, likely increasing cloud coverage. So that could at least
partially offset the impacts of the offshore trends.

Of greater impact is the increase in thunderstorm chances across
the interior through Saturday. Already seeing significant mid and
high level cloud coverage across LA/Ventura Counties today and
models indicate higher PW`s tomorrow and ample instability,
albeit at or above 700mb. The high based aspect to it means the
chances for dry lightning are greater which posed a significant
impact to firefighters tackling the ongoing fires in the area.
Any precip reaching the ground would likely be pretty minimal in
most cases, but with particularly strong storms with strong
updrafts it`s possible that isolated pockets of heavy rain could
develop across the mountains and interior areas. Also, can`t rule
out possible overnight showers tonight, though chances are too low
to include in the official forecast and most of the hi res models
hold off until at least mid morning Saturday. Given the current
flow pattern PW`s drop off towards the west and north so our
western counties would have a higher chance of dry lightning than
the eastern counties.

Models showing the moisture shifting north and east of the area
Sunday and Monday but not totally sold on that.

.LONG TERM (WED-SAT)...12/155 PM.

The upper high that has been causing the extreme heat for so long
is starting to weaken and shift slightly east. And early next week
there will be an onshore trend that will continue the cooling
trend until around Wednesday. As the high shifts east and a weak
upper low develops off the coast of northern California the flow
aloft will take on more of a westerly component which
basically will put an end to any thunderstorm chances.

For the latter half of the week, high pressure is expected to
return from the east bringing warming temperatures to mainly
inland areas. Based on the current ensemble solutions,
high temperatures should stay below advisAVDAFDLOXory/warning levels
through at least Friday with highs 4-8 degrees above normal.
However, the warming trend will continue through next weekend and
there`s at least a 30-40% chance of 110 or higher across the
Antelope Valley and interior SLO County so chances for advisory or
warning level heat are increasing during that time. Not seeing
any significant offshore trends during that time, so while the
warmest coastal valleys will likely be in the 100-105 range,
coastal areas should remain mostly in the 70s.

&&

.AVIATION...13/0713Z.

At 0523Z at KLAX, the marine layer was 1300 feet deep. The top of
the inversion was at 4300 feet with a temperature of 30 deg C.

Moderate confidence in TAFs for KPRB, KPMD, and KWJF. For these
sites, there is a 10% chance for thunderstorms thru 14Z and a 20%
chance 14Z-03Z.

Moderate confidence in TAFs for KBUR and KVNY. There is a 30%
chance of LIFR cigs and IFR vis 11Z-15Z.

Moderate confidence in coastal TAFs. Vis will likely vary
frequently through 15Z. Cig hgts may be off by +/- 300 ft. VFR
transition may be off by +/- 2hours.

KLAX...Moderate confidence in TAF. There is a 30 percent chc of
Cigs remaining AOA OVC005. There is a 30 percent chc that Vis
will remain AOA 3SM. If Vis does drop below 3SM it will likely
vary frequently between 1SM and 3SM. Low clouds may arrive as late
as 07Z tonight. No significant easterly wind component is
expected.

KBUR...Moderate confidence in TAF. There is a 30 percent chance
of 2SM BR OVC004 conds 11Z-15Z.

&&

.MARINE...12/924 PM.

Small Craft Advisory (SCA) conditions are generally not expected
through the weekend. However, there is a 20% chance of SCA winds
in the Outer Waters and far western portions of the Santa Barbara
Channel during the late afternoon through overnight hours
beginning Monday through the week. A long period south swell is
expected to arrive Tuesday and may lead to a chance for elevated
surf conditions and high rip current potential through Thursday.

Dense fog will continue across the coastal waters tonight and
Saturday morning. Please reference the Marine Weather Statement
for additional information.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Excessive Heat Warning remains in effect until 9 PM PDT this
      evening for zones 38-343>345-353-376>379-381>383. (See LAXNPWLOX).
     Fire Weather Watch in effect from 9 AM PDT this morning
      through this evening for zones 342>345-348-351>353-376>383. (See LAXRFWLOX).
PZ...NONE.

&&

$$

PUBLIC...MW/Sirard
AVIATION...Rorke
MARINE...Lewis/Phillips/Cohen
SYNOPSIS...MW

weather.gov/losangeles

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