Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Los Angeles/Oxnard California
918 am PDT Sat Aug 27 2016
High pressure aloft will build into the region through early next
week before being replaced by a deepening low pressure aloft by
mid week, possibly lasting into the weekend. This will result in
a brief warm up to start the week before a prolonged cooling trend
with expanding night to morning marine layer clouds takes hold.
The marine inversion this morning ranged from 2400 ft deep at kvbg
to 2800 ft deep at klax. Low clouds covered the CST and vlys
including a large portion of the slo County nrn interior vlys this
morning. The low clouds will clear back to or just off the CST by
midday to early this afternoon leaving mostly sunny skies across the
region altho a smoke layer may persist in some areas. Moderate
onshore gradients (+6.2 mb lax-dag fcst at 00z from 12z nam) will
bring some gusty S to W winds to the foothills mtns and deserts this
afternoon. Temps today are forecast to be 4 to 10 deg cooler than
normal for the coast and vlys, and near normal to a few degrees
above normal in the mtns and deserts. Highs in the warmest vlys and
foothills this afternoon should reach the mid 80s to around 90,
except mid to upper 90s in the Antelope Vly.
An upper level trof over sern California this morning will move E thru this
afternoon. At the same time, an upper level ridge will start to
build along the central California coast. The ridge will build further into
swrn California tonight thru sun, then persist over the area with 500 mb
heights around 591 dm thru Mon.
The marine layer pattern with night and morning low clouds and fog
for coastal areas is forecast to continue tonight thru Mon. However,
the marine inversion should lower enough tonight to prevent the low
clouds from moving well inland over vtu/l.A. Counties. The inversion
should then lower further to below 1000 ft Sun night into Mon
morning with low clouds confined to the coastal plain except the sba
County S CST should remain clear due to northerly canyon winds.
In addition, patchy dense fog can be expected with the low clouds
Sun night and Mon morning. Some mid level moisture should move in
during the period as well, with a few afternoon cu buildups possible
in the mtns. Otherwise, mostly clear skies will continue thru Mon
altho a smoke layer may persist in a few locations at least into the
weekend. Weaker onshore gradients will persist during the afternoon
and evening hours, with local gusty S to W winds at times in the
foothills, mtns and deserts. Some generally weak offshore flow is
also expected later Sun night into Mon morning, mainly over slo/sba
counties and in the foothills and mtns of vtu/l.A. Counties.
Temps are forecast to have a warming trend sun and Mon, with highs
several degrees above normal away from the coast on sun, and 4 to 10
deg above normal for many areas on Mon. By Mon afternoon, the
warmest vlys and foothills will reach the upper 90s to 102.
***From previous discussion***
A trough of low pressure near 34n and 142w in the Pacific Ocean
will advance towards the West Coast late in the weekend. Southwest
flow aloft will start to develop between Monday night and
Tuesday night. A cooling trend will begin for the central coast on
Tuesday as onshore flow strengthens and the marine layer starts
to deepen. The cooling trend will likely spread to areas south of
Point Conception between Tuesday and Wednesday. Coastal areas
south of Point Conception will likely see some cooling on Tuesday
with better cooling forecast areawide for Wednesday.
A broad trough of low pressure will likely remain anchored along
the West Coast for latter half of next week and bring a cooler
than normal weather pattern to the area. A series of weak cool
fronts will dips south washing out over northern and central
California. These boundaries will likely increase the northerly
surface pressure gradient and bring gusty northerly winds to
southern Santa Barbara County and through the Interstate 5
Marine layer at lax at 0915z is 2300 feet deep and the inversion
top is at 4100 feet with a temp of 20 degrees c.
Moderate confidence in coastal taf sites due to uncertainty in
timing and category of low cigs/vsbys. There is a 20 percent
chance that low cigs linger as late as 22z for klax and koxr. For
tonight, low cigs are expected to start around the same time if
not earlier at all coastal taf sites (excluding kbur kvny and
kprb where VFR cigs are expected to prevail) and generally
similar, if not one flight category lower. There is a 20 percent
chance of LIFR to IFR cigs at kbur kvny and kprb between 28/09z.
Good confidence in kpmd and kwjf tafs with VFR conds prevailing
through the period.
Klax...moderate confidence taf with a 20 percent chance that MVFR
cigs linger as late as 22z. Low cigs are expected to return between
27/03z and 08z with a 30 percent chance of brief IFR cigs.
Kbur...good confidence in taf with VFR conds expected to prevail
after 27/17z. However, there is a 20 percent chance of LIFR to
IFR cigs after 28/09z.
Low end Small Craft Advisory conditions are expected this
evening as northwest winds increase and persist into the early
morning hours across the outer waters from Point Conception to San
Nicholas island. Small craft conditions are expected to be
stronger Sunday late afternoon or early evening, possibly
extending to cover all outer waters from Piedras Blancas to San
Nicolas Island. Localized gale conditions are possible Monday and
Tuesday evening/night across the same area in response to a trough
of low pressure building over the West Coast. Small craft
conditions may extend into the inner coastal waters at times
especially from Point Piedras Blancas to Point Sal and the
western portion of the Santa Barbara Channel.
Small craft conditions due to continuing gusty northwest winds
and steep seas may continue at times across the outer coastal
waters through next weekend.
Pz...Small Craft Advisory in effect from 3 PM this afternoon to 3
am PDT Sunday for zones 673-676. (See laxmwwlox).