Acton Weather

000
FXUS66 KLOX 192045
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
145 PM PDT Mon Apr 19 2021

.SYNOPSIS...19/139 PM.

A cool down with a return of night through morning low clouds and
fog will start tonight and continue through late in the week.
Drizzle or light rain is possible Wednesday into Thursday morning,
mainly for parts of Los Angeles and Ventura Counties.

&&

.SHORT TERM (TDY-THU)...19/143 PM.

An interesting day of trends today as weak onshore flow shifts to
onshore. Interior areas, especially those above 2000` elevation,
warmed up considerably, in some cases as much as 15 degrees from
yesterday. On the other end of the spectrum, coastal areas
generally cooled as much as 15 degrees as the turn to onshore
ushered in that chilly air over the cold Pacific Ocean. The
transition area between the coast and the foothills were very
similar to yesterday.

Going forward, the rest of the week will be much cooler as a
couple of low pressure systems drop out of the north and move
through the state. Onshore flow will continue to increase and the
marine layer will become much more widespread and include the
coastal slopes by Wednesday and Thursday. Still dealing with some
northerly gradients today across the western portion of the Santa
Ynez Range and there could be some brief advisory level wind gusts
there tonight. Will hold off issuing an advisory due to it being
marginal and mostly in low impact areas but people driving through
the Gaviota area will feel some decent gusts this evening. These
winds will also hold off the low cloud push tonight across srn SB
County and Ventura County but clouds should start to fill in early
Tuesday and certainly by Tuesday evening. Likely many coastal
areas will stay cloudy well into the afternoon but expect most
valleys should clear out.

The first upper low Wednesday will mostly stay north and east of
the area but significant cooling aloft will push the marine layer
depth above 3000`. Drizzle was already in the forecast but upped
the ante by adding in some 15-20 pops and light rain chances for
parts of LA County in the morning. Minimal, if any, clearing for
coast and coastal valleys with highs mostly in the low to mid 60s.

The second upper low Thursday is farther west and probably has the
best chance of dropping measurable rain across LA County.
Increased pops 5-10 percent for the morning and added some low
pops in for the afternoon across the LA mountains and Antelope
Valley as models show the airmass becoming slightly unstable. Once
again slow if any clearing for coast and coastal valleys.

Increasing southwest winds expected in the Antelope Valley,
especially the foothill areas this week, possibly reaching
advisory levels at times.

.LONG TERM (FRI-MON)...19/143 PM.

Strong onshore flow to continue Friday and into the weekend,
though the upper lows will be replaced by a weak ridge Friday into
early Saturday that will help warm temps a few degrees and reduce
the marine layer depth and speed up clearing. Models continue to
show a full latitude trough early next week, though differ quite
a bit with rain chances. Basically all of the ECMWF ensembles show
at least a little rain across most of the forecast area Sunday
night into Monday while the GFS ensembles are drier. Interestingly
both the GFS and EC deterministic runs were drier than earlier
solutions, especially southern areas. It`s likely the very early
season typhoon in the western Pacific is causing some issues in
the model runs that may continue for several more days so it may
some time before we have more clarity in the rain situation for
next week. For now, odds favor some rain in most areas by next
Monday, but on the light side.

&&

.AVIATION...19/1812Z.

At 1743Z, there was no marine layer depth at KLAX.

Moderate confidence in the current forecast.  VFR conditions
are occurring at all terminals. LIFR to IFR conditions will
return to Central Coast terminals this evening and Los Angeles
County coastal terminals after 06Z. Conditions will improve to
MVFR south of Point Conception after 12z.

KLAX...VFR conditions will persist through at least 08Z, then
there is a likely chance of LIFR to IFR conditions by 10Z at the
latest. Any east winds should remain less than 7 knots.

KBUR...VFR conditions will persist through 13z. There is a medium
(40 percent) chance of LIFR to IFR conditions after 13Z Tuesday.

&&

.MARINE...19/143 PM.

Moderate to high confidence in the current forecast. Higher
confidence in seas and timing, less confidence in wind speeds.

For the outer waters... Small Craft Advisory (SCA) level winds will
very likely persist through today. Speeds will increase tonight
through Tuesday evening with a GALE WARNING in place. Conditions
should fall below SCA levels Thursday and Friday.

For the inner waters along the central coast... A Small Craft
Advisory will be in place through Tuesday evening.

Inside the southern California bight, SCA level winds will likely
linger during the afternoon and evening hours across the Santa
Barbara Channel today and Tuesday. There is a moderate (30-40
percent) chance of SCA level for the waters between Pt. Mugu and
San Mateo Point. Gusty winds could develop near Point Dume and
through the San Pedro Channel this afternoon and evening.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...Small Craft Advisory in effect until 9 PM PDT Tuesday for
      zone 645. (See LAXMWWLOX).
     Small Craft Advisory in effect until 3 AM PDT Tuesday for
      zone 650. (See LAXMWWLOX).
     Small Craft Advisory in effect until 6 PM PDT this evening
      for zones 670-673-676. (See LAXMWWLOX).
     Gale Warning in effect from 6 PM this evening to 9 PM PDT
      Tuesday for zones 670-673-676. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK (THU-MON).

No significant hazards expected.

&&

$$

PUBLIC...MW
AVIATION...Sweet/Hall
MARINE...Sweet
SYNOPSIS...MW

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