Scientific Forecaster Discussion
fxus66 klox 171137
Area forecast discussion
National Weather Service Los Angeles/Oxnard California
437 am PDT Thu Oct 17 2019
An upper trough crossing to the north of the area will bring a
cooler temperatures to the region today through Saturday. Gusty
northerly winds are expected to increase this afternoon through
early next week, especially across Santa Barbara and Los Angeles
counties. The strongest winds will be tonight into early Friday,
and Saturday night into Sunday.
Short term (tdy-sat)...17/313 am.
Upper level trof is moving through a little faster than expected.
The thick cirrus shield associated with it is also trucking along
at a good clip and will be gone by sunrise. The marine layer is
about 1000 feet deep. There is a 2 mb push to the east while the
north/S grad is near neutral. Marine layer stratus has been reluctant
to form and will likely be confined to the southern portion of la
County and portions of the central coast. Big cool down on tap
today as hgts falls of about 10 dm and onshore flow conspire to
drop Max temps 10 to 20 degrees everywhere except for the
Winds are really the main story for today and most of the rest of
the forecast. Westerly wind with advisory level gusts to 45 mph
will develop in the Antelope this afternoon. Late in the afternoon
and esp during the evening strong north winds will develop as the
north to S grad turns strongly offshore helped along by a little upper
support and cold air advection. Advisory level winds with gust to
50 mph will develop in the sba mtns and South Coast...the I-5
corridor in the la mtns and the Santa Clarita Vly. These strong
north winds will last through sunrise on Friday.
The north winds will pile up clouds on the north facing slopes
along the Kern County line. An eddy is supposed to develop low
clouds for the coastal sections of la County but the way things
have been going lately would not be surprised if skies stayed
Brisk northwest flow sets up over the area on Friday. The offshore grads
from the north will help warm the coasts and vlys of la and vta
counties. Further cold air advection will cool the interior while
the coasts and vlys of sba and slo counties will see little
There will be another north wind event Friday evening but it will
be a little weaker than tonight's still advisories will likely be
needed for the I-5 corridor and the sba South Coast/Santa Ynez
A little trof will ripple through the northwest flow on Saturday. It will
not have much effect on the weather over Southern California during the
day. It will be mostly sunny day with a few degrees of warming
brought about by hgt rises. Max temps will come in about 2 to 4
degrees below normals.
The little trof will usher in a reinforcing shot of cold air for
Saturday evening. Northerly gradients will also increase with the
lax-bfl grad dipping to -6.5 mb and the sba-bfl grad falling to -6
mb. These kind of gradients will likely produce warning level
wind gusts through the I-5 corridor and the sba South Coast.
Strong advisory level gusts will also be likely across much of the
rest of la and vta County notably excluding the San Gabriel Vly.
Long term (sun-wed)...17/321 am.
Both the ec and the GFS agree that the northwest flow will push to the
east on Sunday and that an upper high will take up residence over
srn CA and Monday and persist until Wednesday.
There will be 2 to 3 mb of offshore flow both from the north and the
east. Since the upper high will be overhead there will be no thermal
or upper support with these Santa Ana winds and only non advisory
level 15 to 25 mph canyon winds are expected each morning.
Max temps will be the big story through the period. Hgts rise to
588 dm on sun then to 591 dm on Monday and a rather August like
594 dm on Tuesday. Hgts do fall to 590 dm on Wednesday.
These high hgts and offshore flow will combine to bring well above
normal temps to the area all three days. By Tuesday there will be
more 90 degree readings than readings in the 80s. Max temps will
be 10 to 15 degrees above normal across the coasts and vlys.
Offshore flow will
continue Sunday through Tuesday while at the same time the ridge
over the Pacific will shift east and park itself over the West
Coast. Temps will warm a few more degrees Sunday then really Jump
Up Mon/Tue into the lower 90s for some inland coastal areas and
mid 90s for some of the valleys. With the upper ridge right
overhead upper support for winds will be weakening considerably.
Still expecting some gusty north to northeast winds on Sunday,
possibly advisory levels in some areas. Then much weaker Monday
There will be decent cooling along the coast on Wednesday but only
slight cooling inland as the ridge weakens and the offshore grads
At 0736z at klax, the marine layer was 900 feet deep. The top of
the inversion was near 1900 feet with a temperature of 21 c.
North of Point Conception... high confidence with kprb, ksbp for VFR
conds. 20% chance for ksbp to see IFR cigs between 12-15z this
morning. Otherwise moderate confidence for ksmx with IFR conds
through 17z. There is a 30% chance that cigs could linger an
additional 2 hours. Good confidence in gusty northwest winds across the
central coast this afternoon and evening hours.
S of Point Conception...moderate confidence for VFR conds, but
there is a 30% chance for IFR to low MVFR cigs to develop across
coastal areas of l.A. And Ventura counties from 12-16z this
morning. Higher confidence for ksba and all valley taf sites with
High confidence with strong westerly winds across kpmd, kwjf this
afternoon through the overnight hours.
Klax...moderate confidence in 12z taf. There is a 30 percent chc
that IFR/low MVFR cigs could develop between 12-16z this morning.
There is a 30% chance that east wind component will exceed 8 knots
between 14z-18z. Good confidence for northerly Crosswinds to 8
knots between 05z-10z this evening into early Fri morning.
Kbur....high confidence in to 12z taf. There is a 20 percent
chance of IFR/low MVFR cigs between 13z-15z this morning.
Outer waters...high confidence that Small Craft Advisory northwest wind gusts and steep
seas will continue through mid afternoon, and at that time winds
are expected to increase with gale force gusts during the latter
half of the afternoon. A Gale Warning is in effect from mid- afternoon
through mid-morning Friday for the entire outer waters. After a
brief decrease in winds Friday morning to Small Craft Advisory level gusts, there
is a 50% chance for another round of gale force winds Friday night
Inner waters north of Point Sal...moderate to high confidence in
Small Craft Advisory level winds tonight through Thursday afternoon through late
Thursday night. There is a 20% chance for local gale force winds
Thursday evening. There will be a 40% chance for Small Craft Advisory level gusts
Friday afternoon through the overnight hours, then 50-60% for same
time on Saturday.
For the inner waters south of Point Conception...a Gale Warning
has been issued for the western portion of The Channel from mid-
afternoon through early Friday morning. Otherwise Small Craft Advisory level
westerly gusts can be expected across the eastern portion during
the late afternoon and early evening hours. Winds will increase
over the sba channel again over the weekend.
For the Santa Monica Bay...there is a 40% chance of northerly Small Craft Advisory
level gusts late this evening through early Friday morning. North
to northeast winds should increase from Santa Monica to the
Ventura County line and there will be a 50% chance that a Small Craft Advisory will
be needed for winds through early afternoon hours before winds
shift to the west. And SW to S across the San Pedro Channel.
Hazardous short period seas are expected across all of the waters
during much of the forecast period due to strong winds and large,
steep seas, combined with a long period northwest swell.
A northwest swell will begin to move into the waters early today,
increasing through the day with high surf expected along the
central coast by this evening. The surf will build to 10 to 12
feet on west to northwest facing beaches Thursday night, peaking
with sets to 14 feet by late Friday morning through Friday
evening, and then will gradually subside through Saturday morning.
There is a chance that the surf will remain near or above the
high surf threshold of 10 feet through Saturday evening.
South of Point Conception, the northwesterly component of the
swell means that less of the energy will make it to shore.
However, the west facing Ventura beaches could see surf up to 5 or
6 feet Friday.
California...high surf advisory in effect from 5 PM this afternoon to 8 am
PDT Saturday for zones 34-35. (See laxcfwlox).
Wind Advisory in effect from 6 PM this evening to 6 am PDT
Friday for zones 39-52. (See laxnpwlox).
Wind Advisory in effect from 5 PM this afternoon to 8 am PDT
Friday for zones 54-88. (See laxnpwlox).
Wind Advisory in effect from 4 PM this afternoon to 11 PM PDT
this evening for zone 59. (See laxnpwlox).
Pz...Small Craft Advisory in effect until 3 am PDT Friday for zone
645. (See laxmwwlox).
Gale Warning in effect from 3 PM this afternoon to 3 am PDT
Friday for zone 650. (See laxmwwlox).
Small Craft Advisory in effect until 3 PM PDT this afternoon
for zones 670-673-676. (See laxmwwlox).
Gale Warning in effect from 3 PM this afternoon to 9 am PDT
Friday for zones 670-673-676. (See laxmwwlox).
Hazard potential outlook (sat-wed).
Moderate to strong northerly winds are expected through Sunday,
focused over Santa Barbara and Los Angeles counties. These winds
may produce damaging gusts near 60 mph Saturday night around the
Santa Ynez range and the Interstate 5 corridor. These winds and
moderately dry conditions may result in critical fire weather
conditions in Santa Barbara County. Gusty Santa Ana winds are
possible Sunday into Monday morning with critical fire weather
conditions possible over Los Angeles and Ventura counties.