Area Forecast Discussion
Issued by NWS Los Angeles, CA

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FXUS66 KLOX 300547

1047 PM PDT THU SEP 29 2016

A cooling trend will begin Friday, then temperatures will be near
or below normal Saturday through Monday. A warming trend will begin
on Tuesday. Overnight through morning low clouds and fog will
increase through weekend.


It was another very warm day across the region, with temperatures
generally about the same as on Wed or a couple of degrees warmer
in most areas. There were some buildups in the mountains, and
radar showed a few light echoes during mid to late afternoon,
probably indicative of a few light showers. Once the sun began
to set, any buildups and potential showers quickly dissipated.
Skies were clear across almost all of the region this evening,
although an area of stratus was beginning to push into the Central
Coast. With a shallow marine inversion still in place, expect some
dense fog there as well. Dense fog may become widespread enough to
require advisories for later tonight. The WRF model shows little
in the way of boundary layer moisture s of Pt Conception
overnight/Fri morning, so will continue to forecast of clear
skies. However, there is a slight chance that some stratus will
form across coastal sections of L.A. and VTU Counties late tonight
or early Friday. N-S gradients have been increasing across SBA
County this evening, and there could be a few hours of gusty winds
through and below passes and canyons later this evening.

An upper trough approaching the West Coast will cause heights and
thicknesses to begin to lower on Friday. At the same time, onshore
gradients will increase, and there will be cooling at 850 mb and
950 mb. This should lead to at least a few degrees of cooling in
most areas on Fri, although max temps will still be several
degrees above normal in most areas. High temps will likely
approach or slightly exceed 90 degrees in the warmest locations in
the valleys on Fri, some 4 to 8 degrees above normal for the last
day of September.

***From previous discussion***

A little eddy spinning up Friday night should help increase low
cloud coverage at least for coastal LA County Saturday morning.

Increasing northwest wind behind the trough passage this weekend
will result in gusty sundowner winds as early as Friday night but
then increasing in strength Sat and Sun evenings, possibly to near
advisory levels. Gusty winds also expected in the I5 corridor and
Antelope Valley by late Sunday as well. The northwest winds will
likely limit the northward advancement of the marine lyr.

Daytime temperatures will continue to cool through the weekend as
the trough ushers in cooler air aloft. Highs for coastal areas
only in the 60s and 70s while coastal valleys top out in the low
to mid 80s.


A second trough will move through central California Sunday night
into early Monday. The GFS shows a pretty strong northwest
pattern setting up behind it Monday with very gusty winds in the
usual west/northwest wind prone areas and colder air aloft. The
ECMWF is further north with much less support aloft for strong
winds and not nearly as cool. Have leaned towards the windier and
colder GFS solution for now. Should be quite a windy day Monday in
most areas with lots of wind advisories and possibly some isolated
warning level winds in the mtns and AV.

Winds expected to settle down Tuesday as we transition to a north
and then eventually a northeast pattern Wed/Thu. A ridge building
in from the west will result in rapid warming across the area,
especially by Thu with light offshore flow. At this time models
are favoring a much weaker offshore wind event next week than what
we saw earlier this week and not nearly as hot, but still 5-10
degrees above normal most areas.



At 0540Z, the marine inversion at KLAX was based near 500 feet.
The top of the inversion was 1500 feet with a temperature of 26
degrees Celsius.

Overall, moderate to high confidence in 06Z TAF package.
Overnight, expect only the Central Coast to experience any CIG or
VSBY restrictions with widespread LIFR/VLIFR conditions. Moderate
confidence in areas south of Point Conception remaining VFR
overnight and Friday (20% chance of IFR?LIFR conditions
developing at coastal TAF sites).

KLAX...moderate confidence in 06Z TAF. There is a 20% chance of
IFR/LIFR conditions developing 09Z-17Z.

KBUR...high confidence in 06Z TAF. VFR conditions will prevail
through the period.

.MARINE...29/900 PM...

Areas of dense fog north and west of San Miguel Island will
redevelop tonight. Northwest winds will increase tonight and
Fri, and small craft advisory conditions will exist from Piedras
Blancas to San Nicolas Island Friday afternoon through Monday
with gale force gusts possible each afternoon Saturday through
Monday. Gusty west to northwest winds will likely push into the
southern inner waters and the SBA Channel each afternoon Saturday
through Monday, possibly reaching SCA levels.





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