FXUS66 KLOX 182136
Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
236 PM PDT Mon Mar 18 2019
Following warm and dry conditions today, a storm system will
approach the area on Tuesday...clouds will increase and max
temperatures will fall. Showers are likely on Wednesday along with
some mountain snow and a slight chance of mountain thunderstorms.
The system will move out of the area Thursday and skies will
clear through the day. It will be dry and warmer on Friday.
.SHORT TERM (TDY-THU)...18/230 PM.
Temperatures are down over most of the coastal and valley areas
today as the offshore flow abates and onshore flow takes hold.
Temperatures are still well above normal under sunny skies. Low
visibilities along the coast will be the main issue for tonight
into Tuesday, as a strong inversion and shallow marine layer
will likely create dense fog. This could impact LAX and LGB
airports with travel delays, as well as other coastal airports.
Tuesday will be cooler with temperatures around normal as
pressure gradients turn more onshore, and clouds increase with the
approaching storm. Not much change in terms of the details of
this storm, with minimal impacts expected. Low pressure aloft
currently centered 1200 miles west of Los Angeles will move over
the Central Coast Tuesday night, then move little through
Wednesday. Still looking for rain to be focused during the late
Tuesday night and Wednesday time period. The one change made to
the forecast is expansion of thunderstorms. With plenty of cold
air aloft (-26C at 500MB), there will be marginal instability
first over the coastal sections Tuesday night into Wednesday
morning, then over most of the area Wednesday afternoon and night
as the low moves directly over the region. There remains a fair
amount of uncertainty in regards to rainfall amounts due to the
expected showery nature and thunderstorm factor. In general,
amounts should range between 0.10 and 0.25 inches of Los Angeles
County, and 0.25 and 0.50 inches over the other three counties.
Local amounts up to around 1.00 inches is possible under heavier
showers or thunderstorms. Rainfall rates should generally stay
under 0.25 inches per hour, but could top out at 0.50 inches per
hour basically anywhere under a thunderstorm. The threat for
debris flows are minimal. Impacts will likely stay confined to
travel issues from wet roads. Snow levels should stay in the 5,000
to 6,000 foot range, but could lower to 4,000 feet Wednesday
morning in the most unstable airmass. Could see a dusting of snow
on some mountain roads, but accumulations should stay above 5,500
feet. We may need a Winter Weather Advisory, with Santa Barbara
and Ventura Counties the most favorable, but it is very
borderline. There will be some gusty south winds as well,
especially Tuesday into early Wednesday, but looks under any Wind
Advisories at this point. Temperatures will fall below normal to
Due to the slow movement of the system, we could still see
scattered showers anywhere on Thursday, especially over the
interior areas. Temperatures will remain below normal. As the
center of the low moves further to the east later Thursday, gusty
northwest winds will form and will flirt with a Wind Advisory over
south SBA County and the I-5 Corridor.
.LONG TERM (FRI-MON)...18/235 PM.
Besides some possible showers on the northern slopes, Friday looks
dry and a few degrees warmer than Thursday. A very weak upper
level trough will then pass through northern California Saturday
morning, but whether or not our area receives light rain or
nothing remains a tale between model brothers. The ECMWF continues
to show light amounts over much of the area, while the GFS and 90
percent of its ensemble members are completely dry. This adds up
to a chance of rain for Saturday. Sunday and Monday look warm as
an upper level ridge quickly forms behind the trough, and onshore
flow weakens. Above normal temperatures are possible under such a
At 1717Z at KLAX, there was a 1100 ft marine layer. The top of
the inversion was around 1750 ft with a temperature of 19 degrees
The offshore flow and clear skies of the past few days are
transitioning as low level flow truns onshore and marine clouds
have developed across much of the coastal waters. Most coastal
sections will have marine clouds moving overnight with IFR to LIFR
conditions likely, mainly between 03z-16z north of Point
Conception, and 09z and 16z south. Valley and desert TAF sites
should remain VFR.
KLAX...Low to moderate confidence in the 18Z TAF. There is a 30
percent chance of the marine clouds moving into the airfield plus
or minus two or more hours from the forecasted time. There is a 20
percent chance of east wind issues.
KBUR...High confidence in the 18Z TAF with VFR conds thru the pd.
For the Outer Waters, high confidence in the forecast thru Tue
morning with winds and seas below Small Craft Advisory (SCA)
levels. By Tuesday afternoon into Tue evening, there is a 50%
chance for the northern zone (PZZ670)for southerly winds
increasing to SCA level gusts. On Wed and Thu, there is a 50%
chance of SCA level W to NW winds across the entire outer waters.
For the Inner Waters north of Pt Sal, high confidence in current
forecast through Tue night with winds and seas below SCA levels.
On Wed, there is a 20%-30% chance of SCA level SW winds, and for
Thu there is a 30%-40% chance of SCA level W to NW winds.
For the Inner Waters south of Pt Conception, there is high
confidence that winds and seas will be below SCA levels through
Tue night. On Wed, there is a 30%-40% chance of SCA level W wind
gusts at times, and for Thu there is a 30%-40% chance of SCA level
W to NW wind gusts at times.
A large west swell will affect the coast mainly at west facing
beaches with high surf beginning Tuesday night. A high surf
advisory has been issued for the central coast and the beaches of
Los Angeles/Ventura counties with the biggest impact during times
of morning high tide on Wednesday at west facing beaches. (See
LAXCFWLOX for details.)
Dense fog is spreading across much of the coastal waters at this
time and patchy dense fog is likely to cause sudden reductions in
visibility. (See LAXMWSLOX for details.)
A large west swell is expected to move into the coastal sections
Tuesday night and Wednesday. Due to the west component of this
swell, high surf is also possible south of Point Conception. The
breakers are expected to rise to just above 10 feet on the central
coast and around 4-8 feet south of Point Conception. The strongest
impact will be felt on west facing beaches.
In addition, a significant high tide each morning will probably
cause a bit of beach erosion and minor tidal overflow.
CA...High Surf Advisory in effect from 11 PM Tuesday to 11 PM PDT
Wednesday for zones 34-35. (See LAXCFWLOX).
High Surf Advisory in effect from 5 AM Wednesday to 3 PM PDT
Thursday for zones 40-41-87. (See LAXCFWLOX).
.HAZARD POTENTIAL OUTLOOK (THU-MON).
Showers with a dusting of snow on mountain roads are possible on
Thursday. Gusty northwest winds will create difficult driving
conditions. High surf and dangerous rip currents are expected
over the weekend.
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