085
fxus66 klox 211211
afdlox

area forecast discussion
national weather service los angeles/oxnard ca
511 am pdt sat oct 21 2017

...aviation discussion updated...

.synopsis...

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.

&&

.short term...(tdy-mon)

overall, 00z models in very good synoptic agreement through the
period. at upper levels, ridge will build over california through
monday. near the surface, offshore gradients will strengthen
through the period.

forecast-wise, two main issues through the short term period will
be temperatures and offshore winds. with respect to temperatures,
all ingredients are in place for a significant round of heat for
southwestern california. h5 heights increase from 587 dm today to
594-595 dm by monday with an associated increase in thicknesses.
near the surface, offshore gradients will be on the increase
through monday with the nam forecasting a -5.9 mb lax-dag
gradient monday morning (while the gfs forecasts -4.0 mb). the
combination of these parameters indicate an impressive warming
trend from a few degrees above normal today to potentially
widespread record high temperatures on monday. given the potential
for record heat on monday, excessive heat watches will remain in
effect for the south coast of santa barbara county as well as the
coasts/valleys of ventura and los angeles counties.

as for winds, currently there are some very gusty northerly winds
across the santa ynez range (in southern santa barbara county) as
well as across the mountains of ventura and los angeles counties
and wind advisories will remain in effect for these areas through
10 am this morning for southern sba county and 200 pm for the
ventura/la mountains. by this afternoon, the flow will turn
northeasterly, setting the stage for an extended period of santa
ana winds. at this time, all models indicate increasing offshore
gradients and upper level wind support tonight through monday. so,
northeast winds will be on the increase across ventura and los
angeles counties. at this time, expect advisory-level winds to be
localized tonight/sunday, so will not issue or extend any
advisories at this time. however for sunday night/monday, the
likelihood of widespread advisory-level winds across ventura and
los angeles counties looks pretty good. for san luis obispo and
santa barbara counties, the northeast winds tonight through monday
will be noticeably weaker.

as for clouds, there are some clouds this morning across interior
sections of san luis obispo and santa barbara counties as well as
the northern mountain slopes of ventura and los angeles counties.
these clouds will dissipate later this morning, then clear skies
will prevail across the entire area this afternoon through monday.

.long term...(tue-fri)

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 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 ecmwf indicates
offshore gradients.

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).

&&

.aviation...21/12z...

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 cig periodically through 20z and there is a thirty percent
chance of the cig 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 cig 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
22/10z-17z.

kbur... high confidence in the current taf. vfr conditions will
prevail throughout the forecast period.

&&

.marine...21/200 am...

for the outer waters... winds will diminish today but remain at
small craft advisory (sca) level through monday.

for the inner waters north of point sal... winds will diminish
today but remain at sca level through sunday.

for the inner waters south of point conception... winds will
diminish to below sca level by mid morning. the strongest winds
will be across western sections and the western santa barbara
channel. from sunday night through tuesday, there is a sixty
percent chance of sca level northeasterly winds nearshore from
ventura southward.

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.

&&

.beaches...21/200 am...

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
elevated surf.

&&

.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.

&&

.lox watches/warnings/advisories...
ca...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 53-54. (see laxnpwlox).
     fire weather watch in effect from sunday morning through
      tuesday afternoon 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.

&&
$$

public...thompson
aviation...kj
marine...kj
beaches...kj
fire...gomberg/rat
synopsis...thompson

weather.gov/losangeles

NWS LOX Office Area Forecast Discussion



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