Scientific Forecaster Discussion
fxus66 klox 182318
Area forecast discussion
National Weather Service Los Angeles/Oxnard California
418 PM PDT Fri Aug 18 2017
possible showers and thunderstorms for the mountains of Ventura,
Santa Barbara, and Los Angeles counties and deserts into Monday. A
low will bring overnight low clouds and fog to the coast and some
valleys into next week, the temperatures will be near normal with
a warmup on Thursday and into the weekend as the low weakens.
Seeing the expected buildup of clouds over the Ventura and eastern
la County mountains. Not expecting showers today but it is still
possible. The chance of showers will increase through the weekend
and in to Monday.
Today is another fairly seasonal day with moderate onshore flow
in place across the region. The upper level trough will remain into
next week, but weaken a bit Saturday as 500 mb heights climb
slightly. The 1000-foot marine layer depth this morning should
deepen through the weekend, possibly deepening to near 2000-2500
feet by Monday. Near persistence seems to be the best forecast for
the immediate coastal locales through the weekend and into early
next week. Away from the coast, temperatures will cool for early
next week, after a slight warm-up today and Saturday.
The focus of the forecast for the weekend will be on the instability
associated with the trough. East to southeast flow aloft could
draw in enough moisture to get rain out of the afternoon clouds. Pops
with isolated showers and thunderstorms extended through Monday
but still only at the slight chance level.
By Tuesday the marine layer should deepen as the trough deepens
and slowly lifts out of the region through Wednesday. Night
through morning drizzle cannot be ruled out for the Southland
early next week as the marine layer depth will likely deepen
substantially between Monday and Wednesday. Current forecast keeps
marine layer depths inline with 2000-2500 feet, but a depth up to
near 4000 feet between Tuesday and Wednesday would not be
shocking. A general cooling trend should be expected into midweek
next week as the trough wobbles around and creates ebbs and flows
of the marine intrusion.
Drier southwest flow aloft looks to develop for the latter half of
next week as the trough lifts out. Another weak trough of low
pressure reforms off the Pacific northwest coast and a ridge of
high pressure remains centered over the southeast states. GFS is
still liking a warm up late in the week next week.
At 2320z, the marine inversion at klax was based at 1400 feet.
The top of the inversion was 5300 feet with a temperature of 21
Timing of return of low cigs/vsbys may be off by 3 hours or a
category lower than forecasted (or higher as well for ksmx). There
is a 20 percent chance of IFR cigs/vsbys for kvny and kprb
between 12z and 16z. There is a 20 percent chance that VFR
cigs/vsbys prevail through the period at ksba.
Klax...moderate confidence in 00z taf after 05z. Return of low
clouds is possible between 05z and 11z with a 30 percent of IFR
cigs/vsbys, which would be most likely between 05z and 10z.
Kbur...moderate confidence in 00z taf. Have included a brief
IFR cig for kbur early Saturday morning, but there is a 30 percent
chance that no cig will arrive.
For the outer waters, high confidence in current forecast. Winds
and seas are expected to remain below Small Craft Advisory (sca)
levels through at least Tuesday.
For the inner waters, high confidence in current forecast. Winds
and seas are expected to remain below Small Craft Advisory levels through at least
California...beach hazards statement in effect from Saturday afternoon
through Sunday evening for zones 40-41. (See laxcfwlox).
Hazard potential outlook...(mon-fri)
a high risk of rip currents exists at area beaches through the
weekend, and a beach hazard statement is in effect through Sunday
evening. Isolated showers and thunderstorms cannot be ruled out
for Sunday and Monday.