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Area Forecast Discussion (AFD)

Issued by Los Angeles, CA (LOX)

                            
000
FXUS66 KLOX 171837
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA 
1037 AM PST Mon Dec 17 2018

.SYNOPSIS...17/1035 AM.

Isolated showers will taper off this evening. High pressure will 
build over the next few days, accompanied by northerly winds 
tomorrow and above normal temperatures from Wednesday to Friday.

&&

.SHORT TERM (TDY-WED)...17/920 AM.

Cold front moving through the area this morning more or less just
as expected in terms of rainfall amounts. Areas north of Pt
Conception got upwards of half an inch to an inch while amounts to
the south are much lighter. It's holding together well enough to
drop just barely measurable amounts in Ventura County and it will
probably be similar for LA County. Might be worth increasing pops
just to indicate some hydrometeors falling from the sky but many
areas probably won't even quite reach .01. Skies will be clearing
out this afternoon from the northwest, except likely some
lingering low clouds and fog across interior SLO/SBA and the
Grapevine area later tonight into Tuesday morning.

***From previous discussion***

A pattern switch will occur Tuesday as an east pac will start to 
build in, hgts will rise, and the sfc flow will turn offshore both
from the East and North. There will be 2-4 degrees of warming 
across the coasts and vlys which will bring max temps to near normal
values.

Both the GFS and the EC agree that the ridge will peak Wed and 
Thu with hgts near 585 DM.

There will be offshore flow through the period. The strongest
offshore flow will be from the North. The offshore flow will peak
Wednesday with between -4 and -6 MB grads from both the N and E. 
Right now, however, there does not look like there will be enough 
upper or thermal support to create anything close to advisory 
level gusts.

Max temps will be the biggest news story during this period. Max
temps will soar 4 to 8 degrees on Wed. Temps will rise another 
2 to 4 degrees on Thursday and will make it the warmest day of 
the next 7 with max temps 8 to 12 degrees above normal. There will
be quite a few 80 degree readings on Thursday.

.LONG TERM (THU-SUN)...17/400 AM.

The ridge will be pushed aside on Friday as a trof moves into the
PAC NW. There will be decent onshore trends and grads will be near
neutral. There is a chc some marine layer stratus could develop
over some of the coastal sections. The lower hgts and lack of
offshore flow will drop max temps 6 to 12 degrees but since
Thursday was so warm max temps will still be a little above
normal.

Dry NW flow with lower hgts will set up on Saturday. There will be
more onshore flow. It will be partly to mostly cloudy as well as a
remnants of a dead cold front roll overhead. Max temps will
continue to fall and will end up several degrees below normal.

A weak ridge is will likely form on Sunday and will bring clearer
skies and 3 to 6 degrees of warming.

Way out in FantasyLand...On Christmas the EC shows a weak system
with rain while the GFS keeps all precipitation north of I-80.

&&

.AVIATION...17/1837Z.

At 1800Z at KLAX...there was a 3000 foot moist layer topped by an
inversion with a top at 4300 feet and temperature of 8 degrees C.
These values are approximate as AMDAR data is not available.

Low confidence in the 18Z tafs. A weak frontal system was moving
through the forecast area with light rain showers and frequently
large changes in ceiling and visibility. Conditions will gradually
improve later this afternoon as the frontal system exits the area.
VFR conditions will return tonight, except for KPRB where dense
fog is expected.

KLAX...Low confidence in 18z TAF. There is a 30 percent chance of
IFR conditions tonight. High confidence that there will be no 
east wind component greater than 6 kt.

KBUR...Low confidence in 18z TAF. There is a 30 percent chance of
IFR conditions tonight.

&&

.MARINE...17/958 AM.

Moderate to high confidence in the current forecast. A very large
WNW swell will move through the coastal waters through Tuesday. 
This swell is expected to affect west to northwest facing harbors,
including Morro Bay, where dangerous breaking waves will be 
possible in the harbor entrance. Ventura Harbor could also be 
affected today through at least Tuesday as some of the energy from
the swell filters into the Southern California Bight. In 
addition, breaking waves will be possible in shallower water areas
outside the typical surf zone. Moderate-to-high seas will then 
persist Wednesday through Thursday.

Otherwise, winds should remain below Small Craft Advisory (SCA) 
levels through Thursday except for a 50%-60% chance of SCA level 
gusts Tuesday and Tuesday night for the Northern waters near-
shore and the outer waters, especially PZZ673-676.

&&

.BEACHES...17/1000 AM.

Through Tuesday, a very large long period west- northwest swell 
(290 degrees) will impact the Central Coast, likely bringing very 
large and potentially damaging surf during that time. As a 
result, a High Surf Warning will be in effect for the Central 
Coast due to the high confidence in the event. Surf heights of 18 
to 25 feet are expected across the Central Coast, with local sets 
up to 30 feet possible. 

A Coastal Flood Advisory will also be in effect on the Central
Coast, to coincide with the timing of the High Surf Warning. 
Water could spill into normally dry beaches, beach parking lots 
and harbor walkways. Potential impacts will include beach 
erosion, very strong, frequent rip currents and sneaker waves,
with possible damage to piers and coastal structures. In addition
there is a risk of large breaking waves across the Morro Bay 
Harbor entrance, which could capsize small boats.

Some of this large swell energy is expected to wrap into areas 
south of Point Conception, impacting west- facing beaches of LA, 
Ventura, and southern SBA Counties. High Surf Advisories have been
issued for this area where west- facing beaches will generally 
see 6 to 12 foot breakers, with the highest amounts likely for the
Ventura County Coast. There is the potential for local sets to 15
feet across Ventura Harbor as well, with a 20 percent chance of 
needing to be upgraded to high surf warning thresholds. Surf of 5 
to 8 feet is expected for the Santa Barbara South Coast, highest 
on beaches that have some west exposure, such as Rincon Point. 

High surf could continue through Wednesday morning for all areas.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...High Surf Warning in effect until 9 AM PST Tuesday for zones
      34-35. (See LAXCFWLOX).
     Coastal Flood Advisory in effect until 9 AM PST Tuesday for
      zones 34-35. (See LAXCFWLOX).
     High Surf Advisory in effect until 10 PM PST Tuesday for
      zones 39>41-87. (See LAXCFWLOX).
PZ...Small Craft Advisory for hazardous seas in effect until 2 AM
      PST Thursday for zones 645-670-673-676. (See LAXMWWLOX).
     Small Craft Advisory for hazardous seas in effect until 9 PM
      PST Tuesday for zone 650. (See LAXMWWLOX).
     Small Craft Advisory for hazardous seas in effect until noon
      PST Tuesday for zone 655. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK (WED-SUN).

An extended period of high surf and dangerous rip currents will
continue at all beaches through Thursday. Gusty northerly winds 
are possible into Wednesday morning across southern Santa Barbara
County and through the Interstate 5 Corridor.

&&

$$

PUBLIC...MW/Rorke
AVIATION...Sweet
MARINE...Sweet
BEACHES...Sweet
SYNOPSIS...TF

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