Scientific Forecaster Discussion
fxus66 klox 230005 aaa
Area forecast discussion...updated
National Weather Service Los Angeles/Oxnard California
505 PM PDT Thu Aug 22 2019
Updated aviation discussion
Temperatures will remain slightly below normal at the beginning of
the period with the passage of a weak upper level trough. Coastal
low clouds and fog will spread into coastal valleys tonight,
retreating to the coastal areas only this weekend. Building high
pressure next week will bump temperatures higher, returning to
normal and slightly above normal for next week.
Short term (tdy-sun)...22/216 PM.
Southerly flow really starting to kick in this afternoon as models
have been advertising. Lax profiler winds are all from the
southeast or south, though surface winds are still from the west.
Gradients are still trending onshore and temperatures are down 4-8
degrees on average, though Port San Luis, which was 94 yesterday,
is only in the mid 60s this afternoon.
The forecast through the weekend remains largely in tact. The
marine layer is expected to deepen up to at least 2500' tonight
south of pt Conception and at least 1500' up north. This will push
low clouds well into the coastal valleys later tonight and lower
high temps Friday by another 3-6 degrees on average, though
as much as 10-15 degrees across interior slo County. Low
confidence on the marine layer clearing pattern tomorrow given the
big southerly surge and continuing southeast flow just off the
surface. Theoretically this should help la and Ventura counties
clear out while clouds struggle to clear across coastal slo/sb
counties but confidence not high on this part of the forecast.
A weak eddy circulation is expected to continue into Saturday,
however building high pressure aloft along with weakening onshore
flow is expected to lower the marine layer depth and warm temps by
4-8 degrees, mostly across the valleys and other inland areas.
Marine layer clouds will likely linger at many beaches from Malibu
West but otherwise skies will be sunny.
Slightly warmer again Sunday with better coastal clearing. Warmer
valley areas may be getting close to 100 again. May start seeing
some high clouds drifting over the area from the remnants of Ivo
but models still not showing any lower level moisture as the
clockwise flow around the high over California steers the system
and it's moisture farther to the west so convective chances at
this point remain very low.
Long term (mon-thu)...22/213 PM.
While there will be subtle changes in gradients and the upper
level pattern next week the weather through the middle of next
week is not expected to change much. The GFS and European model (ecmwf) continue
to show the remnants of Ivo riding up and over the ridge and
mostly into northern California Wed/Thu so will have to keep an
eye on this but none of the ensembles are showing any precip so
dry and warm weather expected to continue with highs 2-4 degrees
above normal on average.
At 2330z, the marine layer was 1200 feet deep at klax. The top of
the inversion was around 2700 feet with a temp of 24c.
Moderate confidence overall in the 00z tafs, however there is hi
confidence that low clouds will develop and affect many airfields
tonight into Fri. Low clouds and LIFR/IFR/MVFR conditions are
expected at the coast and Vly airfields starting as early as
0130z at ksmx to as late as 12z at kprb. The low clouds should
clear to VFR by late Fri morning to early Fri afternoon except
linger thru Fri afternoon at koxr. The timing of the onset and
dissipation of the low clouds many be off +/- an hour or two.
For kwjf and kpmd, there is hi confidence in the 00z tafs with
VFR conditions expected through Fri afternoon.
Klax...moderate confidence overall in the 00z taf. Low clouds and
IFR/MVFR conditions are expected from about 04z this evening thru
about 20z Fri. More low clouds with MVFR conditions should move
into the airfield around 03z Fri evening as well. Otherwise, VFR
conditions can be expected. The timing of the onset and
dissipation of the low clouds many be off +/- an hour or two.
Kbur...moderate confidence overall in the 00z taf. Low clouds and
IFR/MVFR conditions are expected from about 08z this evening thru
about 18z Fri. Otherwise, VFR conditions can be expected. The
timing of the onset and dissipation of the low clouds many be off
+/- an hour or two.
High confidence in Small Craft Advisory (sca) winds through
tonight over the outer waters from the central coast to San
Nicolas Island. 50 percent chance of Small Craft Advisory winds for the nearshore
central coast waters. Moderate confidence for winds well below
Small Craft Advisory Friday through at least the weekend.
Moderate confidence for abnormally strong southeast winds over
most coastal waters later tonight into early Friday afternoon.
While 10 to 15 knots will be most common, peak winds between 15 and
25 kt are likely between Point Conception and Orange County at
times. There is a 50 percent chance of reaching Small Craft Advisory criteria.
An abnormally large south to southeast swell from Tropical Storm
Ivo will impact the waters Sunday through Tuesday. There is a
potential for the swell to peak between 5 and 7 feet. A swell
from this direction would cause strong surges around and inside
the vulnerable harbors, especially Avalon and San Pedro/Long
Beach. Large breaking waves near the coast are also likely, which
has a history of capsizing small drifting boats.
Tropical Storm Ivo, currently about 500 miles southwest of Cabo
San Lucas, will generate a southeasterly swell reaching California
Sunday and persisting through Tuesday. The peak of the swell
should occur Sunday afternoon through Monday morning with a period
around 14 seconds. While the peak swell heights will most likely
fall between 4 and 6 feet, there is a chance for a range of 5 and
Dangerous rip currents and large breaking waves on rock jetties
are certain. Surf heights should reach at least 4 to 6 feet over
south facing beaches, with a chance of peak surf reaching 6 to 8
feet especially for Los Angeles County, which would require a high
There is a risk for impactful coastal flooding as well. The
highest tides will be late in the afternoon, and should reach
5.7 to 6.7 feet. If the peak swell ends up 3 to 5 feet, flooding
impacts would be minor and mainly in the form of beach erosion. If
the swell height ends up closer to 8 feet, more impactful
flooding would be expected for the vulnerable areas like Pebbly
Beach in Avalon and the Long Beach peninsula if unprotected.
California...beach hazards statement in effect from late Saturday night
through Tuesday morning for zones 40-41-87. (See laxcfwlox).
Pz...Small Craft Advisory in effect until 9 PM PDT this evening
for zones 645-676. (See laxmwwlox).
Small Craft Advisory in effect from 6 am to noon PDT Friday
for zones 650-655. (See laxmwwlox).
Small Craft Advisory in effect until 3 am PDT Friday for
zones 670-673. (See laxmwwlox).
Hazard potential outlook (sun-thu).
Elevated surf and strong rip currents are possible at area beaches
early next week.