Area Forecast Discussion
Issued by NWS Los Angeles, CA

Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

FXUS66 KLOX 160415

Area Forecast Discussion...UPDATED
National Weather Service Los Angeles/Oxnard CA
815 PM PST Mon Jan 15 2018

A low pressure system north of the area will increase the onshore
flow for more clouds and cooler temperatures into Tuesday. A
storm system will spread the possibility of precipitation from
the northwest Thursday evening, and into all areas on Friday. The
weekend will dry out with clearing skies and a warming trend as
offshore flow develops beneath high pressure aloft.



Satellite imagery showing considerable high clouds continuing to
stream into Southwest California tonight as upper level flow
pattern has turned zonal. An upper level trough and associated
cold front will affect Northern California tonight. This front
will move south and east washing out just north of our forecast
area. There is just a slight chance of a brief shower over the
foothills of NW SLO county on Tuesday morning.

Otherwise just looking for quite a bit of mid and high level
clouds to continue to move into the forecast area through
Wednesday. A near neutral pressure gradient this evening combined
with a shallow marine inversion will bring the potential for some
low clouds and fog across coastal areas tonight into Tuesday
morning, with some of the fog being locally dense. As of 8 pm,
already seeing some low clouds and fog returning to the Central
Coast. Cooling trend to continue tomorrow, with slight warming
expected on Wednesday as a weak upper level ridge of high pressure
builds over the area.

Another upper level trough and associated cold front will approach
the Central Coast on Thursday, with a slight chance of rain by
afternoon for the SLO County Central Coast. The threat of light
rain will overspread the forecast area (including Montecito) on
Thursday night.


The trough of low pressure, rotating around the Aleutian Low
pressure system, is scraping the subtropics today. The storm
system will inject some subtropical moisture and eject out toward
the West Coast through Thursday. A frontal boundary will move
across the region between Thursday and Saturday. PoPs have been
bumped up across the region, mainly between Thursday and Friday.
While moisture parameters are only about 1-2 standard deviations
above the mean, a colder air mass will arrive with this system.
Gusty winds will also likely develop with this storm system.
Rainfall amounts look to range between a tenth and a quarter of an
inch with local amounts up to one-half inch possible. With 700 mb
temperatures dropping to around -10 degrees Celsius, snow levels
will likely fall to between 3500 and 4000 feet. Stay tuned, as
this system could cause snowfall at the top of the Grapevine and
possibly into the foothills of the Antelope Valley.

High pressure aloft should develop for the remainder of next
weekend and warming and drying trend be in play.



At 2330Z at KLAX, there was marine layer with a depth of nearly
600 ft. The top of the inversion was at 1000 feet with a
temperature of 18 degrees C.

The combination of weak onshore flow and a shallow marine layer
depth will bring a threat of IFR conditions to many of the
coastal TAF locations tonight but low confidence in occurrence
and timing due to presence of fairly thick higher level clouds.
There is a 20 percent chance of dense fog with LIFR conditions
at KLAX, KLGB, KSMO, KOXR, KCMA, KSMX, and KSBP later tonight
into early Tuesday morning.

KLAX...Low confidence in the 00Z TAF with arrival and timing of
IFR cigs/vsbys later tonight into Tuesday morning as there is a
chance of no low cigs. However, there is also a 20 percent chance
of LIFR conditions late tonight into early Tuesday morning.

KBUR...Very high confidence in CAVU TAF.


.MARINE...15/800 PM.

For the Outer Waters, high confidence in current forecast. Winds
will most likely remain below Small Craft Advisory (SCA) levels
through Wed night, but could get close to SCA levels in some areas
during the afternoon and evening hours Tue and Wed. A large long
period westerly swell will continue to affect the waters through
Wed. SCA conditions for Hazardous Seas are expected through Wed
night. After a very brief lull, another even larger NW swell will
build again Thu afternoon, increasing through at least Fri, with
wave heights 18 to 20 ft possible. Additionally, winds could reach
SCA levels Wed night through Thu, and will likely reach SCA
levels Fri.

For the northern Inner Waters, high confidence in current forecast.
SCA conditions for Hazardous Seas will continue through Wed
night. After slightly subsiding, seas will build to SCA levels
again Thu, with SCA level winds as well Fri.

For the waters south of Point Conception, winds will remain below
SCA levels through Thu. Seas may build to near or above 10 feet
across the western portions of the nearshore waters late tonight
through Tue night. Even larger seas are expected late in the week
and SCA levels winds are expected Fri.


CA...High Surf Advisory in effect until 6 AM PST Thursday for
      zones 34-35-40-41-87. (See LAXCFWLOX).
PZ...Small Craft Advisory for hazardous seas in effect until 3 AM
      PST Thursday for zones 645-670-673-676. (See LAXMWWLOX).


Possible winter weather issues for the I-5 near the Grapevine
Friday night. Otherwise, no significant hazards expected.



SYNOPSIS...STu/Hall is the U.S. government's official web portal to all federal, state and local government web resources and services.