Area Forecast Discussion
Issued by NWS Los Angeles, CA

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FXUS66 KLOX 252104
AFDLOX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
204 PM PDT Mon Sep 25 2017

.SYNOPSIS...
Gradually strengthening offshore flow will bring a warming and
drying trend with mostly clear skies to the area through this week
and into the weekend. There will be some gusty north to northeast
winds at times over the region, especially below and through
passes and canyons. Temperatures will be a few degrees above
normal for many areas early this week, then increase to much
above normal for late this week and into the weekend.

&&

.SHORT TERM...(TDY-THU)

Offshore flow resulted in a decent bump in temperatures area-wide
today but most noticeably for the coast and coastal valleys where
temps were up about 10 degrees on average. Northeast winds picked
up as well but most areas were well below advisory levels.
Gradients and upper support are expected to increase tonight and
Tuesday morning which will lead to a slight increase in Santa Ana
winds and temperatures. Have opted to not go with wind advisories
at this point though it`s likely one or two spots near the
LA/Ventura county line will get a few hours of advisory level
gusts.

On Wednesday gradients and upper support weaken and models show a
little eddy spinning up and pulling in some low level moisture
from the south that could allow some low clouds and fog to creep
up from the south. But even if low clouds do not form coast/valley
temps should cool a few degrees and potentially more than what is
currently forecast. Some mixed signals for Thu but likely minimal
change overall. Low level temps are warmer but gradients trend
slightly onshore so those factors likely will cancel each other
out. If low clouds manage to work their way into LA County
Wednesday they will likely still be around Thu and forecast highs
will almost certainly be too warm.

.LONG TERM...(FRI-MON)

Models are definitely trending away from the ridge pattern through
the weekend and gradients generally trend more onshore each day.
So a few degrees have been trimmed off the forecast highs and more
trimming may be needed if this continues, especially Sunday into
Monday as both the GFS and ECMWF show a pretty strong upper low
moving into the Pac NW late in the weekend. Low clouds would
likely return by the weekend as well if models don`t flip back
around to a warmer pattern.

&&

.AVIATION...25/1600Z.

At 16Z, there was no marine layer at KLAX.

High confidence in VFR conditions throughout the period.
Moderate-to-high confidence in offshore winds. Periods of moderate
to strong wind shear are possible tonight at mainly terminals
south of Point Conception.

KLAX...VFR conditions are expected throughout the period. There is
a 40 percent chance of moderate wind shear between 00Z and 04Z. There
is 10 percent chance of east winds greater than 7 knots after
07Z.

KBUR...VFR conditions are expected throughout the period. There is
a 50 percent chance of moderate wind shear between 10Z and 18Z.

&&

.MARINE...25/200 PM.

Moderate-to-high confidence in the current forecast. Main concern
is winds for the Outer Waters this evening and across the Inner
Waters tonight and into Tuesday morning.

Marginal Small Craft Advisory level winds will likely develop
late this afternoon across the Northern Outer Waters and continue
through this evening, otherwise winds and seas will remain below
Small Craft Advisory levels through at least Friday. Winds will
likely increase over the weekend.

For the Inner Waters, winds and seas are expected to remain below
Small Craft Advisory levels through Friday. There is a 40 percent
chance of Small Craft Advisory north to northeast winds each
night and morning through Thursday across the nearshore waters
from Ventura south to Santa Monica.

&&

.FIRE WEATHER...25/1130 AM.

A long duration of elevated fire danger expected to continue
across portions of Southwest California through this upcoming
weekend. Weak to occasionally moderate offshore flow is expected
during this period which will continue to support a prolonged
period of very warm and dry conditions to the region.

In the short term, offshore pressure gradients are expected to
peak Today and Tuesday when LAX-Daggett gradients are expected to
range between -3 and -4 mb each morning. There is the potential
for a slight ramp up in upper level support on Tuesday and
Wednesday as computer models continue to show the potential for a
cutoff low pressure system to develop near the Colorado River
Valley. Offshore winds are expected to be the strongest across
the mountains Today and Tuesday with some weakening for Wednesday
(including the Santa Monica Mountains) when gusts between 30 and
40 mph are expected with local gusts to around 45 mph. Gusts
between 25 and 35 mph are likely for wind prone valley and
interior coastal areas. Offshore flow is expected to be weaker on
Thursday and Friday, then potentially nudge upward again by
Sunday.

This prolonged period of offshore flow will bring widespread
minimum humidities between 10 and 20 percent for areas away from
the coast through next weekend, along with poor overnight
recoveries across the mountains, foothills, and wind exposed
locations. In addition, there will be a prolonged period of very
warm temperatures with highs climbing into the 90s much of this
week in the valleys, and triple digit readings possible Friday
through next weekend. The above mentioned fire weather conditions
combined with fuels becoming critically dry will support this long
duration of elevated fire danger, with an increased risk for
large fires and erratic fire behavior. Brief critical fire weather
conditions are likely for areas with strongest winds Today,
Tuesday and possibly Wednesday. Local or brief critical fire
weather conditions may return by Sunday.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...Small Craft Advisory in effect until 9 PM PDT this evening
      for zones 670-673. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK...(THU-MON)
No significant hazards expected.

&&

$$

PUBLIC...MW
AVIATION...Hall
MARINE...Hall
FIRE...Munroe/Gomberg
SYNOPSIS...Sweet

weather.gov/losangeles



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