Scientific Forecaster Discussion
fxus66 klox 211640
Area forecast discussion
National Weather Service Los Angeles/Oxnard California
940 am PDT Sat Oct 21 2017
gusty northwest to north winds will affect much of the forecast
area through this morning. The winds will shift to the northeast
this afternoon with gusty Santa Ana winds persisting through
Tuesday. Temperatures will be on the increase through early next
week with record heat possible Monday and Tuesday. For Wednesday
through Friday, a cooling trend is expected.
Main issues this morning are the northerly winds transitioning to
northeast. Have added a Wind Advisory into the early afternoon
hours for the western San Fernando, Santa Clarita, and eastern
Ventura County valleys as high-res model data shows gusts
reaching 40 mph and the lax-dag pressure gradient is trending 7
mb offshore from 24-hrs ago. Winds remain gusty as far south as
the Santa Monica Mountains as well as the Santa Barbara mountains
and central coast areas. Most of the wind issues in the short-
term will subside later today.
Temperatures started out on the cool side this morning, but have
no where to go but up from here through mid-week. Forecast highs
are above normal and might be a little on the warm side of the
house, but tough to adjust much due to compressional heating
effects from air rolling down the mountain slopes today.
For the afternoon forecast package we will be looking at the
potential for Wind Advisory levels along the central coast tonight
and how that impacts minimum temperatures there. Local Santa Ana
winds expected toward Sunday morning in the typical corridors of
eastern Ventura and western la counties. Will expect a moderate
Santa Ana event to start up Sunday night into Monday when
significant heat impacts will also develop. If all temperature
trends remain in place we will likely be upgrading excessive heat
watches to warnings or advisories for the Monday to Tuesday time
For the extended, 00z models remain in good synoptic agreement
through thurday then start to diverge on Friday. At upper levels,
ridge peaks in strength on Tuesday then a deep trough will drop
across the interior west Wednesday and Thursday. On Friday, the
GFS starts to build a ridge in from the west while the European model (ecmwf)
develops an upper low over the 4-corners area. Near the surface,
offshore gradients will peak on Tuesday then weaken Wednesday and
Thursday, turning weakly onshore by Thursday. On Friday, the GFS
continues with weak onshore gradients while the European model (ecmwf) indicates
Forecast-wise, Tuesday will be a very hot and dry day with another
round of record high temperatures likely for many areas with gusty
Santa Ana winds across the area. So, the excessive heat watch
still looks good for Tuesday along with the high likelihood of
wind advisories for Ventura and Los Angeles counties.
On Wednesday, a noticeable cooling trend will begin as the upper
ridge weakens and weak onshore flow returns to the area. This
cooling trend will continue on Thursday for all areas. For Friday,
will go with near-persistence forecast for temperatures, given the
model discrepancies at this time. Additionally, there could be
some stratus redeveloping across the coastal plain by Friday
morning (and maybe as early as Thursday morning).
At 08z at klax... there was no notable marine inversion per amdar
soundings. At 12z however there was a cloud deck near 1900 feet.
Overall... high confidence in the current tafs. Klgb will have an
MVFR ceiling periodically through 20z and there is a thirty percent
chance of the ceiling impacting klax as well. Otherwise and elsewhere
VFR conditions will prevail. Locally strong and gusty west to
northwest winds continue to diminish across the region then gusty
northwest winds strengthen after 15z at ksbp and ksmx.
Klax... high confidence in the current taf. There is a thirty
percent chance of an MVFR ceiling periodically impacting the terminal
through 18z. Otherwise VFR conditions will prevail. There is a
twenty percent chance of east winds to 10 knots 13z-16z and again
Kbur... high confidence in the current taf. VFR conditions will
prevail throughout the forecast period.
For the outer waters... winds will diminish today but remain at
Small Craft Advisory (sca) level through Monday. Local gusts to
35 knots are possible for a while yet near Point Conception.
For the inner waters north of Point Sal... winds will diminish
today but an Small Craft Advisory for hazardous seas continue through this
afternoon. There is a 40 percent chance of Small Craft Advisory level winds out of
the northeast late tonight and Sunday morning.
For the inner waters south of Point Conception... the strongest
winds will be across western sections and the western Santa
Barbara Channel. From Sunday night through Tuesday, there is a
70 percent chance of Small Craft Advisory level northeasterly winds nearshore from
A large long-period northwest swell will move through the coastal
waters through the weekend. Seas up to 15 feet are likely across
the outer and northern waters. There will be dangerous breaking
waves on the central coast through the weekend with dangerous
conditions in and near harbors. South of Point Conception, the
westerly swell will contribute to continued hazardous conditions
along the coastline through the weekend.
A large long-period northwest swell will move through the coastal
waters through the weekend.
North of Point Conception... a high surf advisory continues through
Sunday morning. Surf will increase to between 14 and 20 feet
through midday then will begin to diminish this afternoon but
remain above 10 feet through Tuesday. Some impacts from these
large and powerful waves and strong currents are the risk of ocean
drowning and sneaker waves that can suddenly overrun previously
dry beaches and jetties. With surf approaching 20 feet along some
northwest facing beaches, low lying beach parking lots, Harbor
walkways and campgrounds could see local coastal flooding during
the peak of the highest surf.
South of Point Conception... a beach hazards statement continues
through Sunday afternoon for surf of 4 to 7 feet with local sets
to 8 feet. Dangerous rip currents are a primary impact of this
Fire weather...21/215 am...
Northerly flow today and tonight is expected to bring a warming
and drying trend along with elevated fire danger to the region.
The strongest winds during this period will remain focused across
the mountains, especially the Interstate 5 corridor and Santa Ynez
Mountains where gusts between 40 and 50 mph can be expected.
These areas will experience the strongest upper level support as
well as strong north-south offshore pressure gradients (lax-
Bakersfield and sba Bakersfield gradients expected to peak
between -6 and -6.5 mb late tonight). A red flag warning is now
in effect for the la/Ventura/Santa Barbara County mountains and
Santa Clarita valley.
From Sunday through Tuesday, there is the potential for a
prolonged duration of gusty Santa Ana winds with hot and very dry
conditions. The strongest Santa Ana winds during this period is
expected to be Monday through Tuesday when gusts between 40 and 50
mph will be possible across wind prone passes and canyons of Los
Angeles and Ventura counties. Record breaking triple digit heat
and humidities lowering into the single digits and lower teens
will be possible during this time. In addition, very warm and dry
conditions during the overnight hours in the mountains, foothills,
and wind prone areas will add to this fire weather threat during
this long duration of dangerous fire weather conditions. A Fire
Weather Watch is in effect Sunday through Tuesday for much of Los
Angeles and Ventura counties, including coastal areas. If fire
ignition occurs, there will be the potential for very rapid spread
of wildfire with long range spotting and extreme fire behavior
that could lead to a threat to life and property.
California...high surf advisory in effect until noon PDT Sunday for zones
34-35. (See laxcfwlox).
Wind Advisory in effect until 10 am PDT this morning for
zones 39-52. (See laxnpwlox).
Excessive heat watch in effect from Monday morning through
Tuesday evening for zones 39>41-44>46-88-547. (See laxnpwlox).
Beach hazards statement in effect through Sunday afternoon
for zones 40-41. (See laxcfwlox).
Wind Advisory in effect until 2 PM PDT this afternoon for
zones 45-53-54-88-547. (See laxnpwlox).
Red flag warning in effect from 6 am Sunday to 6 PM PDT
Tuesday for zones 240-241-244>246-547-548. (See laxrfwlox).
Red flag warning in effect until 10 am PDT Sunday for zone
252. (See laxrfwlox).
Red flag warning in effect until 6 PM PDT Tuesday for zones
253-254-288. (See laxrfwlox).
Pz...Small Craft Advisory for hazardous seas in effect until 3 PM
PDT this afternoon for zone 645. (See laxmwwlox).
Small Craft Advisory in effect until 3 PM PDT Monday for
zones 670-673. (See laxmwwlox).
Small Craft Advisory in effect until 9 am PDT Monday for zone
676. (See laxmwwlox).
Hazard potential outlook...(mon-fri)
near record high temperatures and elevated fire weather
conditions are expected for Monday and Tuesday, especially across
valleys and coasts.