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Area Forecast Discussion (AFD)

Issued by Los Angeles, CA (LOX)

                            
853 
FXUS66 KLOX 231817
AFDLOX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA 
1117 AM PDT Mon Oct 23 2017

.SYNOPSIS...
Strong high pressure aloft and gusty Santa Ana winds will create 
well above normal temperatures and record breaking heat through 
Wednesday. Temperatures will begin cooling, but still above normal
at the end of the week.

&&

.SHORT TERM...(TDY-WED)

Cloud-free, hot, dry, and windy is the general forecast for the
day. Already 88 here in Oxnard and expecting many records to be
broken today and tomorrow. Forecast proceeding as expected so far.

*** From Previous Discussion ***

High pressure aloft will dominate the weather through Wednesday. 
Hgts will be around 594 DM today and Tuesday and will fall to 591 
DM on Wednesday as the ridge weakens. The high pressure and 
offshore flow will keep skies clear through the period.

The offshore flow will be the major story for the next 3 days.
Current gradients are -5.4 MB from KDAG and a healthy -7.5 MB from
KBFL. On Tuesday the east to west KDAG gradient peaks at -8.3
while the north to south KBFL gradient weakens some to -4.8 MB.
This will switch the winds to more of an easterly direction. On
wednesday both grads weaken to -6 MB from the east and -3 MB from
the north. No real winds yet but they will start in the mtns in a
few hours and then mix down to the vlys then the coasts during the dawn
to mid morning period. Winds will peak Tuesday. Fortunately there
is zero thermal support and only a little upper support so this
will be a gradient driven event which for the most part can not
reach warning levels...only strong advisory levels (50 to 55 mph
gusts). There will be a few warning level gusts across the 
ridgetops but thats about it. The winds will diminish Wednesday 
but will remain at advisory levels

The very high hgts (15 DM higher than normal) and offshore flow
will combine to bring record heat both today and Tuesday (highs 
95-105 common) and somewhat uncomfortably warm nights (lows 65-75 
common). This heat poses a concern for heat-related illnesses, 
especially for the elderly and children. Heat warnings/advisories
are in effect for much of the area. Please see the product 
LAXNPWLOX for a detailed description of all heat and wind 
warnings and advisories. Major fire concerns exist as well (see 
fire weather section below). 

Weaker offshore flow Wednesday along with lowering heights will 
bring cooling to most areas, most significant north of Point 
Conception and near the coast. However, temperatures will remain 
well above normal with widespread 80s and 90s.

.LONG TERM...(THU-SUN)

Bad news for people hoping for a cool down both the GFS and the EC
now agree that a tall and skinny 588 DM ridge will set up on
Thursday and persist into Friday only to be replaced by a smaller
588 DM ridge poking in from the SW over the weekend. The only good
news is that there will only be weak offshore flow in the morning
and weak onshore flow during the afternoon so max temps will not
be anywhere as warm as they will be early this week still max
temps will be 6 to 12 degrees above normal over much of the area.
Where there was once hope of some marine layer clouds now it looks
like clear skies will prevail as there is no eddy forecast or any
other low cloud formation mechanisms.

&&

.AVIATION...23/1800Z.

At 1737Z, there was no marine layer at KLAX.

Moderate to strong northeast wind will develop today and continue
through Tuesday in Ventura/LA counties. Gusty surface winds 
and/or LLWS could impact many TAF locations. Conditions will 
remain VFR through the TAF period.

KLAX...high confidence in 18Z TAF. There is a 20% chance of a 9 
knot east wind 12Z-17Z. 

KBUR...high confidence in 18Z TAF. Low level wind shear is
possible through the period.

&&

.MARINE...23/900 AM...

For the Outer Waters, high confidence in current forecast. Winds
and seas are expected to remain below Small Craft Advisory (SCA) 
levels through Friday for PZZ670/673. For PZZ676, there is a 40% 
chance of SCA level northeast winds Tuesday.

For the Inner Waters, high confidence in current forecast. For the
waters north of Point Sal, winds and seas will remain below SCA
levels through Friday. For the waters south of Point Conception,
SCA level winds are likely from Ventura south to Santa Monica
today through Wednesday with the strongest winds in the morning to
early afternoon hours. On Tuesday morning, there is a 40% chance 
of Gale force gusts, but the coverage of these gusts are expected 
to be localized. 

There is a chance that the northeast winds will reach Avalon and 
Two Harbors on Tuesday, but since this is a hot Santa Ana event 
the likelihood of significant winds out that far is small. 30 
percent chance of 10-20 KT winds in the harbors, 10 percent chance
of 15-25 KT.

&&

.FIRE WEATHER...23/900 AM.

A moderate to locally strong Santa Ana wind event will bring 
windy, hot and very dry conditions through Wednesday to much of 
Los Angeles and Ventura Counties. This event is especially
concerning because of the multiple day nature of it, which we have
not seen yet this season and such events have a history of large
fires. The winds will peak on Tuesday with 20 to 30 mph gusting to
50 mph common in the wind prone coastal and valley areas of Los 
Angeles and Ventura Counties, and 20 to 30 mph gusting to 60 mph 
common in the mountains. Minimum humidities of 5 to 10 percent 
will be common through Wednesday, with poor overnight recoveries. 
Widespread record breaking heat will exasperate the situation, 
with highs between 95 and 105 common and lows between 65 and 75 
common. Some windy and hilly locations may only drop into the 80s 
at night. A Red Flag Warning will remain in effect through 
Wednesday as a result. Over San Luis Obispo and Santa Barbara 
Counties, similar heat and dry air is expected, but easterly winds
peaked on Sunday and should locally gust between 20 and 30 mph in
the wind prone areas. As such, elevated fire weather conditions 
exist there. 

With these prolonged weather conditions, and the very dry 
fuels/vegetation, extreme fire behavior is likely if any fire 
ignition begins...threatening life and property. The public 
should be very, very careful with any potential ignition sources 
such as welding and brush clearing equipment, as well as campfires
and cigarettes.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Heat Advisory in effect until 8 PM PDT Tuesday for zones
      34>36-39-88. (See LAXNPWLOX).
     Excessive Heat Warning in effect until 8 PM PDT Tuesday for
      zones 40-41-44>46-87-547. (See LAXNPWLOX).
     Wind Advisory in effect until 2 PM PDT Wednesday for zones
      40-41-44>46-53-54-88-547. (See LAXNPWLOX).
     Red Flag Warning in effect until 6 PM PDT Wednesday for zones
      240-241-244>246-253-254-288-547-548. (See LAXRFWLOX).
PZ...Small Craft Advisory in effect until 3 PM PDT Tuesday for
      zones 650-655. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK...(WED-SUN)
Heat advisory level temperatures may continue for many areas into
Wednesday. Gusty northeast winds will likely impact wind prone 
areas of Los Angeles and Ventura Counties through early 
Wednesday. Hot, dry and windy conditions will likely bring 
continued critical fire weather conditions to some areas 
Wednesday.

&&

$$

PUBLIC...Rorke/jld
AVIATION...Sweet
MARINE...RAT/Kittell/Sweet
FIRE...Kittell
SYNOPSIS...B

weather.gov/losangeles