Area Forecast Discussion
Issued by NWS Los Angeles, CA

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000
FXUS66 KLOX 221817
AFDLOX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
1117 AM PDT Sun Oct 22 2017

.SYNOPSIS...
Gusty offshore winds will strengthen and become more widespread
through Tuesday as many locations have record heat on Monday and
Tuesday. Winds ease on Wednesday and temperatures begin to cool
and possibly drop to near normal by Friday.

&&

.UPDATE...

Forecast is largely on track. Current low end wind advisories look
ok as we should see the typical diurnal bump in winds across the
LA/VTA valleys and Santa Monica Mountains later this morning.
Despite lighter winds early this morning, areas with winds only
experienced low temperatures in the low to mid 70s last night,
several degrees higher than forecasted. As a result, low
temperatures may be bumped up the next couple of nights to follow
trends of increasing offshore flow and heating of the lower
atmosphere. High temperatures will be up everywhere today with
most areas 10 to 15 degrees warmer than yesterday, resulting in
widespread 80s and 90s to the west of the mountains.

The first order of business today will be focusing the upcoming
hot conditions by adjusting high and low temperatures as needed
and making adjustments to current heat products, mainly to add
heat advisories where justified. Will also be looking to issuing
wind advisories for typical areas near the Los Angeles and Ventura
County including the mountains beginning late tonight and
continuing through at least Monday afternoon as winds are
expected to be 5 to 15 mph stronger than experienced so far this
morning. High winds (in excess of 58 mph) are possible across the
mountains of Los Angeles and Ventura Counties near the county
border Monday night into Tuesday and perhaps most likely across
western portions of the Santa Monica Mountains. At this time it
does not look like a high wind watch will be needed, but will be
looking more closely at this as new information becomes available.

&&

.SHORT TERM...(TDY-TUE)

Over the next three days an upper high will build into and
persist over the state. Hgts will start out at 591 DM and then
increase to a rather impressive 597 DM for Monday and then retreat
slightly to 594 DM Tuesday. Offshore easterly gradients will
become more and more offshore (-5 today, -6 Monday and -7.5 on
Tuesday) Northerly offshore grads will peak today (-7 mb) and then
decrease slowly through Tuesday (-5 MB) Clouds will be non
existent leaving only winds and temps to talk about.

Current wind advisories are limping along at the moment but will
likely rev up just after sunrise as the offshore diurnal pattern
peaks. The Central Coast wind advisory looks iffy even though the
NAM has very robust offshore winds forecast. The NAM just seems
to have a habit of over forecasting the Central Coast winds. Would
not be surprised if winds came in at 15 to 25 mph. The wind
advisory for the area surrounding the LA/VTA county line is also
not doing much right now but it will likely pick up at sunrise.
The winds will turn more easterly tomorrow and Tuesday as the
North push weakens and the East push strengthens. The typical
Santa Clarita to Pt Mugu wind axis will set up both days with
advisory level winds about 20 miles either side of the axis.
Stronger gradients and just a touch of upper support may well
bring warning level gusts to the Santa Clarita - Pt Mugu area. The
western portion of the Santa Monica mtns stands the best chc of
warning level gusts Tuesday morning an early afternoon.

The strong offshore flow combined with a very warm airmass will
bring record-breaking heat to much of the forecast area Mon and
Tue. For downtown L.A., the record high for Mon is 98 degrees set
in 1965, and the forecast high is 101, while the record hi for
Tue is 99 set in 1909 and the forecast hi is 102. There will not
be record heat today but max temps will be significantly above
normal for many coastal and vly areas. Overnight lows in the windy
vly and foothill areas will likely be in the 70s to near 80. Excessive
Heat Warnings are posted for the VTU/L.A. County coast and vlys
on Sun and Mon. There is also an Excessive Heat Watch for the SBA
County coast during the period.

Please see the latest Non-precipitation Weather Message (LAXNPWLOX)
for the latest details on the Wind Advisories and Excessive Heat
Warnings and advisories.

.LONG TERM...(WED-SAT)

Both the EC and the GFS agree that the high pressure ridge will
slowly break down Wednesday in response to a fast moving short
wave that scoots into British Columbia. There will still be
offshore flow and some easterly morning winds but both will be
much weaker than Tuesday. Temperatures will drop 3 to 6 degrees
(and more at the beaches) but will still be 12 to 18 degrees above
normal. Depending on how much overnight cooling occurs there may
still be a need for heat advisories.

The long range mdls are struggling to resolve a dynamic high
amplitude flow pattern over the CONUS Thu-Sat. The EC keeps the
area under a cyclonic flow pattern while the GFS builds a high
amplitude ridge over the west coast. The GFS soln is a new one and
for now prefer the more consistent solution of the EC. Will keep
the cooler forecast going with a small return of marine layer
clouds. Max temps should be near or at normal for Fri and Sat.

&&

.AVIATION...22/1800Z.

At 1630Z, there was no marine inversion at KLAX.

Developing offshore flow will keep all sites VFR through the TAF
period. There will be occasional LLWS at most any TAF site.

KLAX...High confidence in 18Z TAF.

KBUR...High confidence in 18Z TAF.

&&

.MARINE...22/900 AM.

Made a few changes to the marine products this morning. The
northeast winds on the central coast that had surged up to around
35 knots earlier were showing a downward trend in the last few
hours. Speeds in zone 645 have been lowered a bit, but a SCA
remains in effect through late tonight. Similarly, zones 670-676
will have an SCA in effect through late tonight for gusty north
winds. Additionally, portions of 676 will also be subject to
northeast winds that will increase across the inner waters south
of Point Conception late tonight and Monday morning. Therefore,
the SCA across 676 will likely be extended into Monday morning.

The strongest winds for Monday and Tuesday will be found directly
below passes and canyons in the southern inner waters from
Ventura to Santa Monica Monday and Tuesday mornings.

The eastern portion of Santa Catalina may also see some local
gusty winds to 25 or 30 knots along with choppy seas Tuesday
morning. This situation will be evaluated more thoroughly as we
approach the critical period.

&&

.FIRE WEATHER...22/930 AM...

From today through Tuesday night, a prolonged duration of gusty Santa Ana
winds with hot and very dry conditions is expected. Northeast winds are
expected to gust between 30 and 45 mph across wind favored passes and canyons
of Los Angeles and Ventura counties today. The Santa Ana winds are expected
to increase in areal coverage and intensity Monday into Tuesday, with peak
gusts between 45 and 60 mph on Tuesday across wind favored portions of Los Angeles
and Ventura counties. The hottest and driest conditions are also expected on
Monday and Tuesday, when triple digit heat and humidities lowering into single
digits and lower teens will be common across coastal and valley areas. Northeast
to east winds gusting between 30 and 40 mph will also bring elevated fire
weather concerns to portions of the Central Coast and higher terrain in San
Luis Obispo County through Monday. Of particular concern will be Monday when
the gusty offshore winds combine with humidities lowering into the
teens(locally single digits) and temperatures rising to between 90 and 100
degrees along the Central Coast.

Very warm and dry conditions during the overnight hours in the mountains,
foothills, and wind prone areas will add to this long duration fire weather
threat. A Red Flag Warning is in effect today through Tuesday for much of Los
Angeles and Ventura counties, and may need to be extended into Tuesday night or
Wednesday as latest model guidance shows lingering offshore winds and low humidities
into that period. The duration, strength, and widespread nature of this
Santa Ana wind event combined with the extreme heat and very dry fuels will
bring the most dangerous fire weather conditions that Southwest California has seen
in the past few years. 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 today for zones
      34-35. (See LAXCFWLOX).
     Wind Advisory in effect until 5 AM PDT Monday for zones
      34-35-51. (See LAXNPWLOX).
     Excessive Heat Watch in effect from Monday morning through
      Tuesday evening for zone 39. (See LAXNPWLOX).
     Beach Hazards Statement in effect until 5 PM PDT this
      afternoon for zones 40-41. (See LAXCFWLOX).
     Excessive Heat Warning in effect from 10 AM Monday to 8 PM
      PDT Tuesday for zones 40-41-44>46-87-88-547. (See LAXNPWLOX).
     Wind Advisory in effect until 2 PM PDT this afternoon for
      zones 44-45-88-547. (See LAXNPWLOX).
     Red Flag Warning in effect until 6 PM PDT Tuesday for zones
      240-241-244>246-253-254-288-547-548. (See LAXRFWLOX).
PZ...Small Craft Advisory in effect until 3 AM PDT Monday for
      zones 645-670-673-676. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK...(TUE-SAT)
Near record high temperatures with excessive heat and critical
fire weather conditions will continue on Tuesday, especially
across valleys and coasts. Gusty northeast winds could impact
mountain areas Tuesday.

&&

$$

PUBLIC...Munroe/Rorke
AVIATION...Sweet
MARINE...Sweet
FIRE...Gomberg
SYNOPSIS...Kj

weather.gov/losangeles



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