Area Forecast Discussion
Issued by NWS Los Angeles, CA

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000
FXUS66 KLOX 202048
AFDLOX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
148 PM PDT Fri Oct 20 2017

.SYNOPSIS...
Widespread gusty northwest winds with many areas under wind
advisories this evening. Northerly, offshore wind and above
normal pressure will develop by Sunday bringing elevated fire
danger. Very hot temperatures are expected early next week in a
Santa Ana event. Record heat is possible for Monday and Tuesday.

&&

.SHORT TERM...(TDY-MON)

Weak cold front and upper level trough moved across the forecast
area today. Light rain showers brought some measurable rain to the
mountains and the most cloud cover, but that is just about to end
as drier air is building over the region. Temperatures were a
good 5-10 degrees cooler than yesterday and as much as 20 degrees
cooler in the mountains. The main impact through this evening is
the gusty west to northwest winds felt across the Antelope Valley,
mountains, and coastal areas. Onshore pressure gradients were
quickly building over 7 mb this afternoon and should peak shortly,
but this has resulted in gusts to 40 mph near Zuma Beach, 25-35
mph along the Ventura Coast, and 40-50 mph across the AV.
Visibilities have been reduced to feet in some areas of the AV due
to blowing dust and is a danger to travelers along highways 14 and
138 until winds decrease later this evening.

Expect wind gusts to remain in advisory levels across many coastal
areas and the AV this evening. However, winds will turn more
northerly across the mountains and Santa Barbara south coast so we
will be extending the advisories into Saturday morning and
afternoon in these areas. Also expect winds to continue to turn
and be from the northeast by daybreak across eastern Ventura and
western Los Angeles Counties in a more traditional Santa Ana
pattern. A few wind advisories may need to be reissued for valleys
and coasts for these winds tomorrow morning. Offshore gradients
only reach about 3 mb but that will be about a 10 mb swing from
onshore to offshore.

Warming and drying starts to build in earnest on Saturday.
Temperatures should push to near 80 degrees for warmer coastal
areas and well into the 80s for valleys in the Santa Ana pattern
and as high pressure builds across the west coast. The Santa Ana
winds will become a little stronger Saturday night for eastern
Ventura and western Los Angeles Counties as offshore pressure
gradients reach 5-6 mb between LAX-DAG. Will need to decide in
future shifts whether winds will be strong enough to warrant
additional advisories in these areas Saturday night into Sunday.

Similar trends are expected for Sunday and Monday. The offshore
gradients could reach 7 mb by Monday morning and by then
temperatures will be nearing record territory with highs well into
the 90s at the coasts and over the century mark for some valleys.
Even the nighttime low temperatures will be very warm in the 70s
for foothill communities. An excessive heat watch will remain in
effect for many areas on Monday. This will be an extended Santa
Ana event with significant heat for this time of the year.
Critical fire weather conditions are anticipated into next week
with details below.

.LONG TERM...(TUE-FRI)

The heat wave will likely peak on Tuesday as Santa Ana winds kick
off another warm start and continue to bring dry, hot air down to
the valleys and coasts. The excessive heat watch extends through
Tuesday and fire weather conditions will remain critical. The only
good news here is that the high pressure ridge slowly begins to
break down along the west coast on Tuesday.

Some moderation in temperatures will occur on Wednesday as
heights aloft fall about 60dm and we should start to see winds
reverse back onshore by late morning and early afternoon. Highs
will likely be 10 degrees cooler for coasts and 5 degrees cooler
or so for valleys on Wednesday. This could still be a critical
fire weather day due to reversing wind direction and continued
very dry conditions. Overall though this will be the break in the
October heat wave that we will be glad to see.

A rather cold and deep upper level trough drops across the Rocky
Mountain front range and the upper Midwest later next week. We
will continue to cool slightly on Thursday, however, another high
pressure ridge will pop up over the eastern Pacific Ocean and
start to shift toward California on Friday. Therefore the cool
down could be short-lived and temperatures may begin to trend
upward by Friday and especially into next weekend.

&&

.AVIATION...20/1825Z...

At 1730Z, there was a deep moisture layer to 4500 feet.

Moderate to high confidence in 18Z TAFs. Light to occasionally
moderate LLWS possible at at all terminals beginning between 00Z
and 06Z and lasting for some terminals through the end of the TAF
period. Except for moderate to occasionally strong LLWS expected
at KBUR, KSBA, KSBP, and KSMX.

KLAX...Moderate confidence in 18Z TAF. There is a 20 percent
chance of north winds gusting to 20 kt between 03Z and 08Z with
light to occasionally moderate LLWS likely during this time. There
is a 30 percent chance of east winds of 10 kt sometime between
09Z and 15Z.

KBUR...Moderate confidence in 18Z TAF. Occasional north wind
gusts to 15 kt is possible between 00Z and 10Z. East winds up to
10 kt are possible after 10Z.

&&

.MARINE...20/915 AM...

For the Outer Waters, high confidence in current forecast. Small
Craft Advisory (SCA) level winds this morning will increase to
Gale force levels this afternoon through tonight. The winds will
diminish on Saturday, but remain at SCA levels through Monday.

For the Inner Waters, moderate confidence in the current
forecast. For the waters north of Point Sal, winds are expected to
increase to Gale force levels this afternoon through tonight. On
Saturday, the winds will diminish, but SCA level winds are
anticipated through Sunday. For the waters south of Point
Conception, SCA level winds are expected through tonight with the
strongest winds across western sections and a 30% chance of Gale
force gusts across the western Santa Barbara Channel. From Sunday
night through Tuesday, there is a 50% chance of SCA level
northeasterly winds nearshore from Ventura southward.

A large long-period NW swell will move into our waters Friday and
persist through the weekend. Seas up to 15 feet are likely 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 contribute to continued
hazardous conditions at the beaches through this weekend.

&&

.BEACHES...20/1245 PM...

A large swell will continue to build across the coastal waters
through this evening. As a result, a High Surf Advisory continues
for the Central Coast through Sunday morning. Surf will quickly
rise to around 10 to 12 feet initially this morning. Surf is
expected to continue increase to between 14 and 20 feet through
early Saturday. 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 along some northwest facing beaches, some 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...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 with respect to
elevated surf (3 to 6 feet with local sets to 8 feet) and
dangerous rip currents. So, the Beach Hazards statement continues
through Sunday afternoon.

&&

.FIRE WEATHER...20/1015 AM.

A weakening cold front will bring isolated showers and drizzle to
portions of Southwest California this morning. The main impact
will be increasing northwest to north winds behind the front which
will bring elevated fire danger to many areas today through
tonight. The strongest winds today through tonight will be focused
across the mountains, Antelope Valley, Central Coast, and Santa
Barbara County south coast where gusts between 40 and 55 mph will
be common. Humidites are not expected to be sufficiently low
during this time to warrant any Red Flag Warnings, however a
drying trend will beginning to occur across downslope portions of
the mountains overnight.

Northerly flow on Saturday and Saturday night 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. A Fire Weather Watch is in effect for the mountains
beginning Saturday morning and will likely be converted to a Red
Flag Warning later today.

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 for all mountain and valley areas of
Los Angeles and Ventura counties Sunday through Tuesday, and may
need to be expanded into coastal areas as we draw closer to the
event.

&&

.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 PM PDT this evening for
      zones 34-35-40-59-88. (See LAXNPWLOX).
     Wind Advisory in effect until 10 AM PDT Saturday 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 Saturday 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 from 3 AM Saturday to 10 AM PDT
      Sunday for zone 252. (See LAXRFWLOX).
     Red Flag Warning in effect from 6 AM Saturday to 6 PM PDT
      Tuesday for zones 253-254-288. (See LAXRFWLOX).
PZ...Gale Warning in effect until 9 PM PDT this evening for zone
      645. (See LAXMWWLOX).
     Small Craft Advisory in effect until 4 AM PDT Saturday for
      zones 650-655. (See LAXMWWLOX).
     Small Craft Advisory in effect until 3 PM PDT this afternoon
      for zones 670-673-676. (See LAXMWWLOX).
     Gale Warning in effect until 3 AM PDT Saturday for zones
      670-673-676. (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...Boldt
AVIATION...Munroe
MARINE...RM
BEACHES...RM
FIRE...Gomberg
SYNOPSIS...jld

weather.gov/losangeles



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