Scientific Forecaster Discussion
fxus66 klox 190330
Area forecast discussion
National Weather Service Los Angeles/Oxnard California
830 PM PDT Wed Oct 18 2017
night and morning low clouds and fog can be expected for the
coast and some valleys through Fri, otherwise fair skies and
cooler temperatures will prevail across southwestern California
through the rest of the week. There will be gusty west to north
winds mainly for the mountains and deserts at times. High pressure
will build into the area this weekend for gusty offshore flow and
well above normal temperatures into the middle of next week.
Strong northerly gradients this evening over sba County (e.G., -5.1
mb sba-smx at 02z) resulted in gusty northwest to north winds below
and through the passes and canyons over the sba County South Coast
and adjacent mtns this evening. Some gusts between 35 and 45 mph
have been observed, and will continue thru the rest of the evening.
Locally gusty northwest winds up to 35 mph have also been observed
along the I-5 corridor in northwest l.A. County this evening.
Skies over the region were mostly clear this evening, except for
some low clouds along portions of the central coast. The low clouds
should expand a bit over the central coast thru the night, although
some offshore flow will likely keep the low clouds relatively close
to the coast. The marine inversion at vbg at 00z was rather shallow
at around 800 ft deep, which should help any low clouds lower
overnight and develop patchy dense fog. S of pt Conception, an eddy
is forecast to develop over the socal bight and help to form low
clouds which should push into the l.A. County coast overnight and
possibly into the San Gabriel Vly late tonight, and vtu County coast
around sunrise. The marine layer was 700 ft deep at lax this
evening, and patchy dense fog cannot be ruled out with any low
clouds late tonight. Otherwise, mostly clear skies will prevail
across the region thru the night.
Weak upper level ridging will be over the forecast area tonight into
Thu morning. This will be followed by lowering 500 mb heights Thu
afternoon thru Fri as an upper level trough approaches the California coast
from the east pac into Thu evening then moves mainly over central and
northern California Thu night into Fri morning. A surface cold front is
expected to mostly dissipate just north of slo County Fri morning. The
upper trof will move east later Fri and Fri night, with upper level
ridging building along the California coast on Sat.
There will be some low clouds along the coastal areas Thu morning,
otherwise generally fair skies with some hi clouds at times can be
expected thru Thu afternoon. The marine layer will deepen Thu night
with low clouds expected to expand well inland, and combined with
moisture from the dissipating front later Thu night into Fri
morning, there will be mostly cloudy skies for much of the region at
that time. The dissipating cold front should bring some clouds to
the north mtn slopes by early Fri as well. Partly cloudy skies should
prevail across the region Fri afternoon and evening, then mostly
clear skies can be expected later Fri night through Sat as offshore
Some offshore flow night and morning hours can be expected over
slo/sba counties and interior vtu/l.A. Counties thru Thu morning.
Gusty North Canyon winds will continue each evening over the sba County
S coast and mtns thru Fri, with the strongest winds expected Fri
night, likely to advisory levels. Gusty northwest winds can also be
expected in the l.A./Vtu County mtns mainly along the I-5 corridor
and into the Antelope Vly Fri into Fri evening, then winds will turn
northerly later Fri night into Sat morning. Winds are expected to
reach advisory levels at times thru the period. As the winds turn
more northerly later Fri night they should also affect portions of
the Santa Clarita Vly, San Fernando Vly, sern vtu County vlys and
Santa Monica range, with advisory level gusts not out of the
question at times into Sat morning. Finally, gusty NW winds possibly
to advisory levels along the central coast Fri afternoon will turn north
and NE Fri night into Sat morning.
Temperatures will be considerably cooler on Thu but still around or
slightly above normal for most areas, then temps should fall to a
few degrees below normal overall for Fri. Temps on Sat will warm up
for areas S and west of the mtns, where above normal temps can be
expected, especially from the sba County S coast thru l.A. County.
For the interior vlys of slo and sba counties, and the mtns and
deserts, temps will remain several degrees below normal.
***From previous discussion***
Strong high pressure aloft will develop Sunday and last a good
portion of next week while a cold trough sets up over the eastern
part of the US. The offshore flow which began Saturday will
increase Sunday then mostly level off in the 3-5mb range through
at least the middle of next week. Not much in the way of upper
level support so winds probably will remain below advisory levels.
However, this event is expected to be at least a few degrees
warmer than the previous Santa Ana event earlier this week when
coastal temps were in the upper 90s. So with this upcoming event
highs in the lower 100s seem reasonable for coastal areas away
from the immediate coast and a few degrees warmer for the valleys,
peaking Monday and Tuesday, then just minor cooling Wednesday.
Record highs in this period are mostly in the upper 90s so there
could be quite a few new records set next week. We'll likely need
at least heat advisories for much of la/Ventura counties and
At 2308z, the marine inversion at klax was 500 feet deep. The top of
the inversion was at 2200 feet with a temperature of 25 degrees
Moderate confidence overall in the 00z tafs. Low clouds and LIFR/IFR
cigs are forecast to develop overnight at ksbp, ksmx, koxr, kcma,
ksmo, klax and klgb, with the onset of the low clouds expected from
04z at ksmx to 14z at kcma. The low clouds are forecast to persist
into late Thu morning to early Thu afternoon, then VFR conditions
should prevail thru the rest of the afternoon. The timing of the
onset and dissipation of the low clouds may be off +/- an hour or
two. There is a 30-40 percent chance no low clouds will affect koxr
and kcma. There is also a 30 percent chance the low clouds may
scatter to VFR at ksbp by 12z Thu.
For kprb, ksba, kbur, kvny, kwjf and kpmd, VFR conditions are
expected thru Thu afternoon. However, there is a 20-30 percent
chance IFR cigs could affect kbur late tonight into mid morning Thu.
For ksba, there is a possibility of low level wind shear this
evening due to gusty North Canyon winds in the vicinity. For kwjf and
kpmd, there should be gusty west winds at these airfields by early Thu
Klax...moderate confidence overall in the 00z taf. Low clouds and
IFR cigs are forecast to develop by 08z tonight then improve to MVFR
cigs by 18z Thu before scattering to VFR around 20z. The timing of
the onset and dissipation of the low clouds may be off +/- an hour
or two. Low clouds and MVFR cigs are then expected back at the
airfield by 03z Thu evening.
Kbur...generally hi confidence in the 00z taf. VFR conditions can be
expected at the airfield thru Thu afternoon. However, there is a 20-
30 percent chance IFR cigs could affect the airfield late tonight
into mid morning Thu.
For the outer waters, high confidence in current forecast. Small
Craft Advisory (sca) level winds are expected to continue through
Sunday. There is a 40% of gale force winds Friday and Saturday.
For the inner waters, moderate confidence in current forecast. For
the waters north of Point Sal, there is a 30% chance of Small Craft Advisory level
winds this evening then a 60% chance of Small Craft Advisory level winds each
afternoon/evening Thursday through Saturday. For the inner waters
south of Point Conception, Small Craft Advisory winds has prevailed across western
portions of zone 650 this evening then there is a 70% chance of
Small Craft Advisory winds Thursday and Friday in the afternoon and evening for
both zones 650 and 655.
A large storm off western Canada will generate 40 foot seas in
that area. This will produce a large long-period northwest swell, moving
into our waters by Friday. Seas up to 15 feet are likely, with 20
foot seas possible across the outer and northern waters. There
will likely be dangerous breaking waves on the central coast
through the weekend with dangerous conditions in/near harbors.
South of Point Conception...the westerly swell will approach high
Central coast...a significant storm system in the Gulf of Mexico
has caused large swells to develop. These large northwest swells
will approach the central coast by Friday morning. A high surf
advisory has been issued valid for the central coast Friday
morning through Sunday morning. Surf will quickly rise to around
10 to 12 feet initially Friday mid morning. By Friday evening
through early Saturday, surf should increase to between 14 and 20
feet. Surf will then begin to lower through Saturday afternoon
into Sunday morning, but remain above 10 feet. Some impacts from
these large and powerful waves and strong currents would be the
risk of ocean drowning. Also sneaker waves can suddenly overrun
previously dry beaches and jetties. With surf approaching 20 feet,
some low lying beach parking lots, Harbor walkways and
campgrounds could see local coastal flooding during the peak of
the highest surf.
S of pt. Conception...
A fairly significant long period south swell will continue to move
across coastal waters through Thursday afternoon bringing elevated
surf between 3 and 6 feet for south facing beaches. However, gusty
west winds are forecast to develop across the Ventura coast and
the short period wind waves could pile up to the surf zone causing
local sets to 7 feet Thursday afternoon through early evening.
There is high confidence of strong rip currents during this
period. A beach hazards statement remains in effect through this
The large northwest swell forecast to bring very large surf to the
central coast should filter some of the energy into the Southern
California bight allowing for higher surf potential by this
weekend. Confidence is high at least another beach hazards
statement will be needed or possibly a high surf advisory if surf
is expected to be higher. Will continue to monitor the situation.
California...high surf advisory in effect from 6 am Friday to noon PDT
Sunday for zones 34-35. (See laxcfwlox).
Beach hazards statement in effect through Thursday evening
for zones 40-41. (See laxcfwlox).
Pz...Small Craft Advisory in effect until 10 PM PDT this evening
for zone 650. (See laxmwwlox).
Small Craft Advisory in effect until 3 am PDT Thursday for
zones 670-673-676. (See laxmwwlox).
Hazard potential outlook...(sat-wed)
hot temperatures and elevated fire weather conditions are
expected Sunday into early next week as another Santa Ana wind
event develops. Record heat is possible for Monday and Tuesday.
Large surf and strong rip currents are expected along central
coast beaches Saturday and Sunday.