Scientific Forecaster Discussion
fxus66 klox 170609
Area forecast discussion...updated
National Weather Service Los Angeles/Oxnard California
1009 PM PST Sat Nov 16 2019
Clear skies and offshore winds will keep temperatures well above
normal on Sunday, with record highs possible. Some areas will be
windy, especially through passes and canyons in Los Angeles and
Ventura counties. A low pressure system mid-week will bring
cooling, clouds, and a chance of rain and mountain snow.
Short term (sat-tue)...16/818 PM.
Cutoff low pressure system centered off the coast of northern baja
today while an upper level ridge of high pressure was building off
the coast of California. This pattern yielded offshore flow that
brought significant warming and drying to much of the region
today. Warmest coastal/valley locations climbed into the upper
80s to lower 90s today, with Camarillo Airport tying a record high
of 93 degrees. The lax-Daggett gradient peaked at -3.8 mb this
morning and is still currently at -3.0 mb as of 8 PM this
evening. The NAM and European model (ecmwf) models continue to indicate the peak
lax-Daggett gradient is expected to be around -5 to -5.5 mb on
Sunday morning. Current weather observations showing northeast
winds generally gusting between 20 and 35 mph this evening, and is
expected to ramp up overnight into Sunday morning, as the
offshore gradient increases.
Peak Santa Ana winds are expected to generally range between 30
and 50 mph across wind prone areas of Ventura and Los Angeles
counties late tonight into Sunday morning. There has been good run
to run consistency of this offshore flow event with the NAM/WRF
and European model (ecmwf) models (including ensembles). The increased Santa Ana
winds combined with slight warming of the boundary layer will
likely result in temperatures being a few degrees warmer in most
areas on Sunday. In fact, some coastal and valley areas could
break records on Sunday with highs climbing into the lower to mid
90s across warmest locations. In addition, wind prone areas and
foothills will remain warm tonight, with some areas remaining in
the 70s. The record breaking heat will bring some moderate heat
impacts to coastal/valley areas on Sunday, but due to the very dry
air in place and short duration of event, will hold off on
issuing an heat advisories at this time. The combination of gusty
Santa Ana winds, warm temperatures, very low humidities, and very
dry fuels will bring critical red flag conditions to Ventura and
much of Los Angeles counties. Please see fire discussion below for
more details. It will remain breezy in the foothills and
mountains Sunday night with poor overnight humidity recovery.
*** From previous discussion ***
Monday will remain a warm and dry day with elevated to brief
critical fire weather conditions in the Ventura and Los Angeles
County foothills and mountains. Locally gusty northeast winds
should remain below advisory levels. By afternoon would expect a
reversal to onshore flow for the coasts and valleys with
temperatures starting to cool later in the day. However, a few
locations could flirt with record highs again prior to the arrival
of the seabreeze.
Monday night and Tuesday will be a period of transition as heights
fall and the flow turns much more onshore during the period. Mid
and high clouds will increase on Tuesday with afternoon
temperatures a solid 10-15 degrees cooler than Monday. A cold
front will also be dropping down the central coast in the
afternoon and could generate an isolated shower. This storm system
is associated with low pressure circulation currently viewable on
GOES imagery in the northern Pacific Ocean near 41n/165w.
Long term (wed-sat)...16/152 PM.
Our first storm system of the season will arrive late Tuesday
night into Wednesday as an upper low closes off near sfo Bay and
drops over southwest California, possibly lingering through
Thursday. There has been significant differences in deterministic
model data on exactly what storm track this system will take and
that makes a big difference on how much moisture it will bring to
the region. The ecm has been the most generous as it keeps the low
off the coast longer with a better jet placement and upper
diffluence which could generate isolated thunderstorms and heavy
downpours on Wednesday. However, the GFS takes the low inland much
faster with less support for convection. At this point there is
high confidence in rain for Wed-Thu, but it's still too early to
pinpoint thunderstorm potential and total rain amounts. Ranges for
now are zero in slo co. To a maximum of 0.75 inch in eastern la
co. The ensembles support an average amount of 0.75 inch in la, so
this remains in our forecast. We will continue to closely watch
this system for the potential of heavier rainfall intensities due
to several new burn scars in the recent months.
This system will definitely knock down temperatures with highs
struggling into the mid 60s for many valleys and coasts Wed-Thu.
Snow levels will drop to 6000 ft or less during this event, so
it's likely we will see the First Mountain snow of the season as
well. By Friday, precipitation should come to an end as this
system moves to our east. High pressure will build in from the
north with increasing heights and a rebound in temperatures
heading into next weekend.
At 0530z at klax, there was no marine layer. There was a sfc
based inversion with a top of 1500 feet with a temperature of 26
High confidence tafs...except for klgb where there is a 40 percent
chc of LIFR cigs/vis through 07z-16z. Offshore flow will strengthen
after midnight with low level wind shear in and around hier trrn.
Klax...high confidence in taf, except a 20 percent chance of MVFR
Kbur...high confidence in ceiling and visibility unlimited taf. Lgt turbc surface-140 13z-22z.
For the outer waters, moderate to high confidence in current
forecast. For Sunday and Monday, high confidence in winds and
seas remaining below Small Craft Advisory levels. On Tuesday and Wednesday, high
confidence in Small Craft Advisory level winds and seas with a 20% chance of gale
force gusts. On Thursday, moderate confidence in conditions
dropping below Small Craft Advisory levels as winds and seas subside.
For the inner waters north of Point Sal, high confidence in
current forecast. Winds and seas will remain below Small Craft Advisory levels
through Monday. On Tuesday and Wednesday, high confidence in winds
and seas increasing to Small Craft Advisory levels. On Thursday, winds and seas are
expected to drop below Small Craft Advisory levels.
For the inner waters south of Point Conception, moderate to high
confidence in current forecast. There is a 70% chance of Small Craft Advisory level
northeast winds Sunday morning into Sunday afternoon from Ventura
southward to Malibu. Otherwise, winds and seas are expected to
remain below Small Craft Advisory levels through Tuesday. On Wednesday, there is a
60% chance of Small Craft Advisory level westerly winds.
A moderately high northwest swell with a long period between
14-16 seconds will continue to affect the coastal waters adjacent
to the central coast through Sunday morning. A high surf advisory
remains in effect through 10 am Sunday morning for the central
A beach hazards statement also remains in effect for the beaches
of Ventura County and exposed west facing beaches across the Santa
Barbara South Coast through 3 PM Sunday afternoon.
Although most of the swell energy will remain across the outer
waters, some limited swell energy will continue to move into the
the inner waters south of Point Conception. The main focus for
elevated surf and strong rip currents will be aimed for the
exposed west facing beaches of la/Ventura counties and exposed
west facing beaches across the Santa Barbara South Coast. Elevated
surf between 3-6 feet is expected for these locations through
Sunday afternoon. With high temperatures along the coast expected
to be in the 80s to lower 90s this weekend, local beaches will
likely be busy this weekend. The combination of elevated surf with
long period swells will bring the likelihood of dangerous rip
currents to these locations.
Fire weather...16/753 PM.
A red flag warning is in effect for Ventura County and for the
mountains, and Santa Clarita and San Fernando valleys of l.A.
County for 1 am to 6 PM Sunday.
Northeast winds gusting to 20 to 35 mph are affecting the wind
prone areas of all four counties this evening. Meanwhile
humidities are generally ranging between 15 to 20 percent.
Elevated to locally brief critical conditions are expected
to continue this evening.
Late tonight through Sunday, the northeast winds will weaken some
over Santa Barbara and San Luis Obispo County, while strengthening
over Los Angeles and Ventura counties with gusts in the 30 to 50
mph range, with isolated higher gusts in the most wind-prone
areas. Widespread minimum humidities will fall into the 8 to 15
percent range, and temperatures will rise to the 80's to mid 90's
in many areas, near or above record highs for this time of year.
This will result in widespread critical red flag conditions for
much of Los Angeles and Ventura counties during the warning
period. Sunday night through Monday will remain warm and dry, but
wind gusts will weaken significantly to 15 to 35 mph and will be
confined to only the most wind prone areas. Elevated conditions
will continue, but red flag conditions are not expected.
California...high surf advisory in effect until 10 am PST Sunday for zones
34-35. (See laxcfwlox).
Beach hazards statement in effect through Sunday afternoon
for zones 39-40. (See laxcfwlox).
Wind Advisory in effect from 2 am to 3 PM PST Sunday for zone
40. (See laxnpwlox).
Wind Advisory in effect until 3 PM PST Sunday for zones
44>46-53-54-88-547. (See laxnpwlox).
Red flag warning in effect until 6 PM PST Sunday for zones
240-244>246-253-254-288-547. (See laxrfwlox).
Pz...Small Craft Advisory in effect from 3 am to 3 PM PST Sunday
for zones 650-655. (See laxmwwlox).
Hazard potential outlook (tue-sat).
A cooler and showery weather pattern is expected Wednesday
through Friday next week. Brief heavy downpours are possible,
especially Wednesday to Thursday morning. High surf is likely at
all beaches late Tuesday through early Thursday.