Area Forecast Discussion
Issued by NWS Los Angeles, CA

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FXUS66 KLOX 251803

1103 AM PDT Tue Oct 25 2016


The weather will be dry and slightly warmer today and tomorrow
across the region. A cold front will bring locally gusty
southwesterly wind on Thursday and the possibility of moderate to
heavy rain late Thursday and early Friday. A cloudy and cool
Saturday will be followed by another chance of rain on Sunday.



Minor updates to the forecast today to adjust cloud coverage and
lower temperatures a couple of degrees. There were minimal clouds
over the 4-county area this morning with the exception of mid-
level moisture skirting across northern San Luis Obispo Co. There
was also a patch of dense fog in the SBA Channel between Santa
Barbara and Santa Rosa Island. Temperatures were starting out many
degrees cooler than yesterday at this time, so have lowered highs
from the previous forecast. All else looks fine as a broad
southwest flow aloft remains overhead and the typical afternoon
southwest wind gusts over the mountain passes into the Antelope
Valley. Only expect partial clouds over northern areas with

NAMBufr soundings for both LAX and VBG show a shallow marine layer
forming for Wednesday morning so expect more areas of fog and low
clouds to start the day near the coast. South to southwest flow
aloft will continue to be over the region Wednesday so
temperatures should climb despite the morning coastal issues.

***From Previous Discussion***

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 afternoon.


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 1609Z at KLAX...there was just a hint of a marine inversion
with marine layer depth of 700 feet.

Moderate confidence in the 18z TAFs. VFR conditions will continue
through this evening followed by IFR conditions and marine clouds
affecting many of the coastal sections later tonight into

KLAX...Moderate confidence in the 18z TAF. There is a 30 percent
chance of the marine clouds arrivig plus or minus two hours or
more in the onset of marine clouds.

KBUR...Good confidence in the 18z TAF. VFR conditions are
expected for the next 24 hours.


.MARINE...25/900 AM

There is high confidence that winds and seas will remain below
SCA levels through at least Thu. 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.





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