Area Forecast Discussion
Issued by NWS Los Angeles, CA

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257
FXUS66 KLOX 171831
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
1131 AM PDT Sat Apr 17 2021

.SYNOPSIS...17/259 AM.

A warming trend will continue through the weekend with very warm
temperatures expected on Sunday and Monday with weak offshore
flow. A cool down with a return of night through morning low
clouds and fog is expected for the latter half of next week.

&&

.SHORT TERM (TDY-MON)...17/819 AM.

The marine inversion early this morning was near 1300 ft deep at
VBG and near 2000 ft deep at LAX. Low clouds covered the Central
Coast early this morning, as well as the northern interior SLO
County vlys, the L.A. County coast, San Gabriel Vly, and eastern
portions of the San Fernando Vly. All the low clouds are expected
to clear back to or off the coast by late this morning. Otherwise,
sunny skies will prevail across the forecast area thru this
afternoon. There were slight offshore pressure gradient trends to
the E this morning, and also over SBA County from SBA-SMX. This
has resulted in locally gusty NW to NE winds over the foothills
and mtns, with the highest gust of 36 mph at both the Gaviota RAWS
and SCE Magic Mtn Truck Trail as of 7 AM. It looks like the
offshore flow will continue thru this afternoon over interior
areas, while onshore flow is expected for the coast and some
adjacent vlys. Temps today should warm to several degrees above
normal away from the coastal plain, but remain a few degrees below
normal along the coast. Highs in the warmest vlys and lower mtns
are expected to reach the upper 70s to low 80s.

A large positively tilted upper level trof extending from the
Great Basin into CA today will slowly move S tonight with a cutoff
upper level low developing over AZ on Sun. This will give swrn CA
a broad NW flow aloft today, veering to N to NE tonight and Sun.

Gradients will turn more offshore to the N and E tonight into Sun
morning, with the NAM fcst LAX-DAG gradient at 12Z Sun at -4.1 mb
(- 4.4 mb 24-hour trend) and LAX-BFL falling to -3.7 mb (-2.6 mb
24-hour trend). These offshore gradients and trends combined with
minor upper level support should bring a round of gusty mainly
sub-Advisory NE winds to the area tonight and Sun morning,
including coastal areas by daybreak Sun. Local gusts to near
Advisory-levels cannot be ruled out in the foothills and mtns of
VTU/L.A. Counties.

The offshore flow is expected to keep low clouds away from the
coast tonight and Sun with mostly clear skies prevailing across
the forecast area. However, a few low clouds may affect the far
southern L.A. County coast later tonight. Temps will warm
significantly on Sun and should be 4-14 deg above normal just
about everywhere. Highs should reach the 80s to around 90 for much
of the coast and vlys.

Upper level ridging is forecast to be along and off the CA coast
Sun night then move inland while weakening on Mon. H5 heights over
swrn CA will be around 577 dm on Mon. Weaker offshore flow is
expected Sun night into Mon morning, with increased onshore flow
for the most part Mon afternoon as pressure gradients trend
strongly onshore. Skies are expected to remain mostly clear across
the region thru Mon. Temps will warm further to 10-15 deg above
normal for inland areas, with a few degrees of cooling along the
coast but still slightly above normal there overall. Highs on Mon
for inland coastal areas, vlys and lower mtns should be in the mid
80s to low 90s.

.LONG TERM (TUE-FRI)...17/335 AM.

The deterministic GFS and ECMWF solutions still show some subtle
differences in the extended period from Tuesday through Thursday
due to position and speed of upper level impulses moving across
the western portion of the CONUS. Both do show, however, a
significant increase in onshore flow as well as lowering heights.

The strong onshore flow will bring significant night through
morning low clouds to most of the coasts and vlys on all four
days. There will likely be more than a few beaches that will see
no clearing in the afternoon.

On Thursday morning many ensemble members of both the EC and the
GFS favor a more westward track of one of the impulses. The energy
assoc with this impulse could interact with the deep marine layer
and bring some drizzle or light rain to the csts/vlys/cstl mtn
slopes Wed night through Thu morning.

There will be significant cooling both Tue and Wed. By Wednesday
cst/vly temps will only be in the mid 60s to lower 70s. Not much
change on Thursday and then some warming on Friday as hgts begin
to rise.

&&

.AVIATION...17/1831Z.

At 1801Z at KLAX, the marine layer was 2200 feet deep. The top of
the inversion was at 3000 feet with a temperature of 15 C.

Good confidence in the 18z TAFs, except low confidence in the
central coast TAFs. Marine clouds are expected to make a brief
appearance on the central coast tonight, before increasing
offshore flow pushes the clouds out to sea. There is also a 50
percent chance the central coast may be clear through the period.

KLAX...Good confidence in the 18z TAF. There is a 20-30 percent
chance of marine clouds tonight. High confidence that there will
be no east wind component greater than 5 kt.

KBUR...Good confidence in the 18z TAF. VFR conditions are
expected.

&&

.MARINE...17/1106 AM.

High confidence in widespread Small Craft Advisory (SCA) level
winds continuing through late tonight from the Central Coast to
San Nicolas Island including the western portion of the Santa
Barbara Channel. Models are continuing to indicate winds
diminishing dramatically by early Sunday morning as offshore flow
develops. However, since offshore flow still looks to be weak,
northwest flow over the waters will strengthen by late Sunday
afternoon or early evening. Moderate confidence that winds will
strengthen back to SCA level by Sunday evening across the same
waters, but models seem to be overestimating wind speeds across
all of the waters. Confidence is higher for SCA conditions to
return Monday afternoon and will likely last through at least
mid-week. The gusty winds through the week will produce choppy,
short-period seas that will be dangerous to mariners.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...Small Craft Advisory in effect from 3 PM this afternoon to 9
      PM PDT this evening for zones 645-650. (See LAXMWWLOX).
     Small Craft Advisory in effect until 5 AM PDT Sunday for
      zones 670-673-676. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK (MON-FRI).

No significant hazards expected.

&&

$$

PUBLIC...Sirard/Rorke
AVIATION...Sweet/Stewart
MARINE...Sweet/Stewart
SYNOPSIS...Stewart

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