Area Forecast Discussion
Issued by NWS Los Angeles, CA
FXUS66 KLOX 251121
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
421 AM PDT Tue Oct 25 2016
A weak upper ridge will bring dry weather through early Thursday,
and there will be some warming today and Wednesday. An upper low
and its associated frontal system will bring rain to the region
late Thursday through Friday, then scattered showers could linger
into early Saturday. Another storm system may bring some rain to
the region late Saturday night through Sunday night, then dry
weather is expected Monday with seasonable temperatures.
Skies were mostly clear across the forecast area early this morning
with the exception of some patchy low clouds and local dense fog
across the south coast of SBA County and the portions of the Central
Coast. An area of mid and high level clouds was streaming into
California just to the north of the forecast area as a weak
frontal system moves into Central CA. Do not expect any rain from
this system, but the mid and high clouds on the southern end of
the front should push into areas north of Pt Conception for a
while today. Elsewhere, while it will start of mostly sunny,
there was a fair amount of low level moisture, so expect some
stratocu to develop once daytime heating commences. Heights and
thicknesses will begin to rise today as an upper ridge bulges into
the region from the south. Max temps should be up a couple of
degrees in most areas today.
The upper ridge across the area will amplify tonight and Wednesday
as a trough deepens in the Eastern Pacific. The wrf does show a
fair amount of boundary layer moisture in coastal areas tonight,
and with warming aloft, a marine inversion will likely develop.
Expect at least some low clouds/fog in coastal areas tonight and
Wed morning. Otherwise, skies should be mostly clear. Max temps
should rise several degrees on Wed, especially in the valleys
where highs will likely rise above 80 degrees in many areas.
The sharpening upper trough in the Pacific will pinch off into a
closed upper low Wed night well to the west southwest of the
forecast area. This system will begin to open up as it move
east northeastward on Thu, with increasingly strong swly flow
aloft developing across the region. Mid and high clouds will
begin to increase across northern sections late Wednesday night,
then overspread the remainder of the forecast areas on Thursday.
Across L.A. and VTU Counties, there will likely be a fair amount
of sunshine, especially in the morning, and with rather high
heights and thicknesses, max temps will likely be rather warm,
especially in the valleys, where highs should reach or exceed 80
degrees. With thicker cloud cover farther north and west, it will
be cooler on Thu. Increasingly strong and moist southerly low
level flow ahead of an approaching frontal system will bring a
chance of rain to SLO and SBA Counties Thu, mainly in the
.LONG TERM...(THU NIGHT-MON)
There continue to be a fair amount of uncertainty concerning the
details of the storm system that will affect the region Thursday
night and Friday. All models show the upper low opening up and
weakening as it moves into central California late Thursday night
and Fri morning. As it tracks to our north, its associated sfc
frontal system will sweep across the region. At this point, it
looks as though the best chance of rain across SLO and SBA
counties will be Thursday night, and during Friday morning
and early afternoon across VTU and L.A. Counties. Lingering
moisture will keep a chance of showers in most areas behind the
front later Friday and Friday night, and possibly into early
The system will be tapping into a rich subtropical moisture with
PW values near 1.5 inches. SLO and SBA Counties will be under the
favorable left front quadrant of a nearly 100 knot south
southwesterly jet, and models show some strong upward motion in
that area Thursday night. Conditions look favorable for some tstm
activity with the front Thu night. In addition, decent south to
southwest low level flow will provide good orographic enhancement
of the rainfall across the mountains of SLO and SBA Counties as
It appears as though the heaviest rain from this system will
fall across SLO and SBA Counties, possibly extending into
western VTU County. Model all show the frontal system losing
some punch as it pushes into eastern VTU County and L.A. County.
However, the WRF model shows it holding together reasonably well
all the way through L.A. County, so there is a potential for heavy
rainfall even there. Snow levels will be very high, with any snow
confined only to the very highest peaks.
It is too early to be confident with rainfall totals, but there is
the potential for 1 to 2 inches across much of SLO and SBA
Counties, with 2 to 4 inches in the foothills and mountains.
Across VTU and L.A. Counties, there is the potential for one half
inch to one inch of rain, with higher amounts in the mountains,
especially across wrn VTU Counties where totals could be in the 2
to 3 inch range. Rainfall rates could reach one half inch per
hour, especially from wrn VTU County northward. This is all
subject to change based upon later model runs, but the potential
certainly exists, even across L.A. and VTU Counties for mud and
debris flows in and below recent burn areas.
Weak ridging will bring generally dry weather Saturday into
Saturday night. A weak system may bring some light rain to the
region late Sat night through Sun night, but it does not look like
a major system. Dry weather is expected Monday with seasonable
At 945Z at KLAX...there was no marine layer nor an inversion.
Moderate confidence in TAFs. There is a 20 percent chc of IFR cigs
at any coastal TAF site until 16Z.
KLAX...Moderate confidence in TAF. There is a 20 percent chc of
IFR cigs until 16Z.
KBUR...Good confidence in TAF. There is a 10 percent chc of
LIFR cigs until 16Z.
There is high confidence that winds and seas will remain below
SCA levels through at least Wed night. South to southeast winds
will likely reach SCA levels by Thursday night for the outer
waters as the next pacific storm moves into the region.