Area Forecast Discussion
Issued by NWS Los Angeles, CA

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000
FXUS66 KLOX 170430
AFDLOX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
830 PM PST Mon Jan 16 2017

.SYNOPSIS...
Offshore flow and mild weather will continue through Tuesday. A
low pressure system approaching from the northwest will bring an
increase in clouds and cooling on Wednesday. Rain and mountain
snow is expected at times Wednesday night through Monday as
several storm systems move through the region.

&&

.SHORT TERM...(TONIGHT-THU)

Mostly clear skies across the forecast area this evening as weak offshore
flow prevails. The offshore flow will get slightly stronger
overnight into Tuesday morning, bring some breezy conditions
across the passes and canyons of LA/Ventura counties. Otherwise
look for clear skies with slight warming across the region on
Tuesday.

For Tuesday night and Wednesday, flow will shift to southwesterly
and an eddy is forecast to develop over the bight. So, will expect
some redevelopment of low clouds Tuesday night/Wednesday morning
(although confidence in coverage of low clouds is still low).
Additionally, there will be increasing mid/high level clouds
during the day on Wednesday in advance of first storm forecast to
impact the area. With increasing clouds and onshore flow,
Wednesday will be a cooler day.

Current thinking on series of storms still on track. For the first
storm, the Central Coast should see the majority of its rainfall
on Wednesday night, then spreading into Ventura and LA counties
for the Thursday morning commute. With 00z NAM and GFS showing a
pocket of instability with good cold air advection aloft (500 mb
temperatures in the -23 to -26 degree celsius range), have
introduced a slight chance of thunderstorms for Thursday morning.
If this materializes, we could see some locally higher rainfall
totals as well as potential beach lightning on Thursday morning.
In evening update, will nudge up expected rainfall totals for
first storm to now mostly range between 0.50 and 1.00 inch with
locally higher totals for south facing slopes. Could see some
minor mud/debris flow issues with this first system, but not
anticipating a need for a Flash Flood Watch with storm #1 unless
thunderstorm probability increases.

*** From previous discussion ***

Snow levels will start out above 8000 feet on Wednesday, but will
drop to around 5000 feet during the day on Thursday. There will
likely be a few inches of snow accumulation at the resort level
and some type of winter weather product may be needed as the event
draws closer.

.LONG TERM...(FRI-MON)

Overall, 12Z models remain consistent and in pretty good agreement
through the period as a very unsettled pattern will persist across
southwestern California.

On Friday, the second in the series of storms will sweep across
the area. Rain should begin across the Central Coast early Friday
morning then spread southward across Ventura/Los Angeles counties
during the day, exiting Los Angeles county by late afternoon with
scattered showers possible Friday night and Saturday. This system
looks to be a bit more potent on all models (especially the GFS)
as stronger southerly flow ahead of the front will help with
orographic enhancement of the rainfall. At this time, rainfall
estimates are for between 0.50 and 1.50 inches (with local amounts
up to 2.50 inches possible in the more favored upslope areas).
Rainfall intensities with this storm could reach problematic
levels for the recent burn area. As for snow, this storm looks to
be a bit colder. Snow levels will start out around 5000 feet
Friday morning, but will drop to between 3500 and 4000 feet Friday
night and Saturday. Snowfall accumulations will likely be more
impressive with accumulating snowfall at lower elevations than the
Thursday storm.

For Sunday and Monday, the wet and unsettled weather will
continue. Both the GFS and ECMWF move a third storm across the
area on Sunday which could be even more potent than Friday`s
storm. For Monday, the model solutions do diverge as the GFS
brings another storm across the area while the ECMWF just keeps a
showery pattern over the area. Either way, there is the distinct
possibility of Sunday/Monday being the most impressive of all the
storms over the next 7 days.

&&

.AVIATION...16/2330Z...

At 2330z at KLAX... there was a weak inversion around 700 feet.
The top of the inversion was around 1500 feet with a temperature
of 13.5 degrees celsius.

High confidence in the 00z TAFs. Increasing low level offshore
flow overnight into Tuesday morning should keep TAF sites VFR
through period. Only concern will be low clouds and fog possibly
spilling into KPRB from the east, but only a 20 percent chance.
There is a 10 percent chance of mvfr cigs redeveloping at KLAX
and KLGB tonight.

KLAX...High confidence in the 00z TAF. VFR conditions expected
through period. Only a 10 percent chance of MVFR cigs redevelopingovernight.
Light northeast to east winds expected to develop overnight into
Tuesday morning, but speeds expected to remain below 6 knots.

KBUR...High confidence in VFR conditions through period.

&&

.MARINE...16/800 PM...

Outer waters and northern inner waters...Northwest winds will be
below Small Craft Advisory (SCA) levels through Wednesday
afternoon. Southerly winds expected to increase ahead of a cold
front Wednesday and will reach SCA levels Wednesday night. A slight
chance of thunderstorms and rain will accompany the front.
South winds will increase to SCA levels again late Thursday night
into Friday morning along with another frontal passage...with gale
force gusts possible over the northern waters. Moderate to strong
northwest winds will follow behind the front through Saturday.

For the Inner Waters south of Pt Conception...Light winds are
expected through Wednesday afternoon then southerly winds will
increase on Wednesday ahead of a frontal system but are likely to
remain below SCA levels. Slightly stronger southerly winds for
Thursday night into early Friday ahead of another front.
Increasing northwest winds behind the front Friday afternoon into
Saturday will likely reach SCA levels. Slight chance of
thunderstorms expected for THursday morning.

A fairly large long period swell will affect the waters through
Tuesday. Another large long period swell will arrive early Wednesday...
then a very large swell is forecast to arrive Friday night into
Saturday. This third swell will be the largest...potentially
reaching heights over 20 feet at 18 seconds over the northern
outer waters late Friday night into early Saturday.

&&

.BEACHES...07/800 PM.

A long period westerly swell will bring elevated surf to the
Central Coast, L.A and Ventura beaches through Tuesday. Another
larger swell will bring rising surf later in the week with High
Surf conditions expected Thursday through Monday for all areas.
There is a good chance of very large westerly swell developing
Friday into Saturday...potentially resulting in very large,
damaging surf for area beaches. The best chance of damaging surf
will be on the Central Coast late Friday and Saturday, where surf
between 20 to 30 feet is likely. Less certain is damaging surf
south of Point Conception, but surf heights may rise to near 15
feet on west-facing beaches. During this time...expect strong rip
currents in all areas and dangerous, rough surf due to strong
south wind waves and large westerly swell. Coastal erosion will
be likely, with a possibility of sneaker waves and coastal
flooding.

Beach goers should use the highest level of caution during this
time. Much larger waves could wash over rocks, jetties and beach
areas near the water`s edge, potentially sweeping you into the
water. West facing harbor entrances will be dangerous with large
breaking waves. Breaking waves may also occur in shallow water
near the outer edge of the surf zone.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Beach Hazards Statement in effect from late Wednesday night
      through Monday evening for zones 34-35. (See LAXCFWLOX).
     Beach Hazards Statement in effect from Thursday morning
      through Monday evening for zones 39>41-87. (See LAXCFWLOX).
     Beach Hazards Statement in effect through Tuesday evening for
      zones 40-41. (See LAXCFWLOX).
PZ...NONE.

&&

.HAZARD POTENTIAL OUTLOOK...(THU-MON)
A wet and unsettled weather pattern is likely Wednesday night
through Monday. The heaviest rain during this period will probably
fall on Friday and again later Sunday and Monday. There is a chance
of damaging warning level surf and coastal flooding issues starting
Friday and continuing through Saturday, especially along the
Central Coast.

&&

$$

PUBLIC...Gomberg/RAT
AVIATION...Gomberg
MARINE...Smith
BEACHES...Smith
SYNOPSIS...Sukup

weather.gov/losangeles


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