Area Forecast Discussion
Issued by NWS Los Angeles, CA

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FXUS66 KLOX 171021

321 AM PDT Thu Aug 17 2017

After a little break this morning...night through morning low
clouds and fog will continue through the period. Weaker onshore
breezes and a shallower marine layer will bring a few degrees of
warming through Saturday, even though temperatures will remain a
bit below normal in most areas. Another weak trough will develop
Sunday which will deepen the marine layer and cool temperatures.



The marine layer has collapsed and is trying to reform (and not very
successfully) The latest AMDAR sounding from KLAX show a weak
1400 ft marine layer capped by a very weak inversion. Gradients
continue to trend offshore. Currently there are some low clouds
along the Central Coast but skies south of Pt Conception are
clear. Some clouds are forming south of LA county and by dawn
about a third of the LA county coast will have stratus with just
a few patches of stratus along the Malibu strip and the Ventura
county coast. Hgts rise in the wake of the departing upper trof
and this along with the increased sunshine and offshore trends
will bring a decent warming trend to the area. Still temps will be
below normal everywhere except for the Antelope Vly and interior
of SLO county.

The marine layer will be better organized tonight but it will be
fairly shallow so only expecting coastal low clouds with the vlys
remaining clear. The vlys and inland areas will see another degree
or two of warming Friday as hgts peak but the better marine layer
will knock a couple degrees from the coastal highs.

Saturday will be very similar to Friday as there are little to no
changes in the meteorological parameters.


Both the EC and the GFS agree that a trof will arrive on Sunday.
On Monday a cut off low will develop at the base of the trof to
the west of the area. This low will the spin in about the same
place through Tuesday and then move overhead Wednesday. Look for
the cyclonic flow of the trof/upper low to lift the marine layer
deep into the vlys.

The temperature forecast is a little tricky as all guidance is
keep temps that seem a little too warm for such a deep marine
layer pattern. This might be explained by the gradients which are
only weakly onshore due to the sfc reflection of the upper low to
the west of the area. The weak gradients combined with hgts that
are not that low (588 DM) and the warm August sunshine may explain
the warmer max temps. Will hole with the guidance for now but if
the marine layer is more stubborn than fcst max temps could well
be 3 to 6 degrees cooler than fcst.



At 09Z, the marine layer depth was around 1400 ft deep at KLAX.
The top of the marine inversion was around 2300 ft with a
temperature near 19 degrees Celsius.

Low confidence in coastal terminal forecast...moderate confidence
all remaining sites. At coastal terminals, there is a chance of
IFR to MVFR conditions through 18Z, and again after 04Z tonight.
The earliest arrival is likely for Central Coast terminals
tonight, later at coastal terminals South of Point Conception.

KLAX...There is a 40 percent chance of MVFR conditions through
18Z, and again after 06Z tonight. Otherwise, VFR conditions will
likely persist throughout the period.

KBUR...VFR conditions are expected throughout the period, except
for a 20 percent chance of LIFR to MVFR conditions between 13Z and


.MARINE...17/300 AM.

Moderate to high confidence in the forecast. Winds should remain
below Small Craft Advisory levels through early next week. There
is a 40 percent chance of Small Craft Advisory conditions
developing on Friday afternoon and evening across the Southern
Outer Waters. There is 20 percent chance of Small Craft Advisory
conditions across the Santa Barbara and San Pedro Channels each
afternoon and evening through the weekend.




No significant hazards expected.



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