Area Forecast Discussion
Issued by NWS Los Angeles, CA
FXUS66 KLOX 271207
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
507 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.
A trough of low pressure centered over the Great Basin will
continue to move over the area today. Onshore flow with a deep
marine layer will remain in place across the area today. The
latest marine layer depth at KLAX AMDAR soundings suggests the
marine layer currently near 2400 feet early this morning. The
latest fog product imagery shows marine layer stratus well-
entrenched this morning and will likely push into the higher
valleys and coastal foothills later this morning. With marginal
instability with trough moving over the area, an isolated shower
or two cannot be ruled out over the mountains this afternoon and
High pressure aloft near 22N and 128W, or about 1000 miles south-
southwest of Los Angeles will build in for the start of next week
and bring a warming trend for early next week. Temperatures will
warm to 5 to 10 degrees above normal for this time of year. In the
warmest valley locations such as Woodland Hills, Ojai and Paso
Robles, daytime high temperatures will exceed the century mark on
Monday. A thinning marine layer depth will take place through
Monday, with a chance of no stratus for areas south of Point
Conception. North of Point Conception, stratus will likely hug
the Central Coast into the afternoon and evening as a strong
marine inversion will develop.
A developing northerly surface in the wake of the trough on
Sunday will likely bring increasing northerly winds through the
Interstate 5 Corridor and Sundowner Winds to Southern Santa
Barbara County each afternoon and evening. At this time, winds
will likely remain below advisory levels, but locally gusty winds
could impact the Gaviota area of the Santa Barbara South Coast and
some of the windier peaks near the Interstate 5 Corridor in Los
Angeles and Ventura County Mountains.
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 early Sunday
morning 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 Pierdas Blancas to San
Nicholas 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 Pierdas 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).