Area Forecast Discussion
Issued by NWS Los Angeles, CA

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FXUS66 KLOX 201752

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
1052 AM PDT Fri Apr 20 2018

Updated Aviation Section

.SYNOPSIS...20/928 AM.

High pressure and offshore flow will bring above normal temperatures
from Friday into Monday. An eddy will usher in overnight coastal
low clouds and fog from Saturday into Monday. Then a low should
arrive by Tuesday for increasing onshore flow and a cooling trend
through Friday.


.SHORT TERM (TDY-SUN)...20/912 AM.

The upper low has exited the area and a weak ridge of high
pressure will take its place through Saturday. Already seeing
decent warming aloft and some of that will translate to the
surface as well so some warming today and more so Saturday,
especially inland. Coastal areas will still have a marine layer
and light onshore flow to deal with so quite a bit cooler there.
With the ridge building today the marine layer depth should lower
overnight and there could be some areas of dense fog, especially
north of Pt Conception.

***From previous discussion***

Overall, Saturday and Sunday will be fairly similar. A weak to
moderate eddy will spin up low clouds and fog to coastal areas
south of Point Conception by morning each day. A weak Sundowner
may delay the onset of low clouds for the SBA South Coast Sunday
night. Away from the coast temperatures will be warmer with highs
in the mid 70s to mid 80s common.

.LONG TERM (MON-THU)...20/333 AM.

Below normal confidence continues for later next week. This is
mainly due to the erratic and hard to predict nature of cut-off
low pressure systems.

Ridging aloft will gradually weaken, giving way to gradually
increasing onshore flow through the middle of next week ahead of
slow moving cut-off low pressure system approaching from the west.
Slowly lowering heights and an earlier sea breeze making it
further inland should combined to provide a gradual cooling trend
for much of next week. The southwesterly flow and lowering heights
should help develop low clouds across the remainder of southwest
California and low clouds possibly making into valley areas by the
middle of next week. Mid and high clouds are possible at times
with high level moisture riding up and over the ridge. The
increasing onshore flow will likely support breezy onshore winds
for the interior starting early next week.



At 17Z, the marine layer at KLAX was 1800 feet deep. The top of
the inversion was 3000 feet at 12 degrees Celsius.

High confidence in VFR conditions everywhere through 01Z with
seasonal onshore flow. 40% chance of IFR ceilings at KSMX 01-06Z,
likely clearing by 08Z. Ceiling possibilities after 06Z...80%
KSBP KPRB. Low confidence on ceiling heights, with anything
between 005-015 possible.

KLAX...High confidence in VFR through 06Z with seasonal onshore
flow. 80% chance of ceiling tonight with arrival window of 06-10Z.
If ceilings form, 60% chance of low-MVFR, 30% chance of IFR, 10%
chance of LIFR. SE winds will form again after 08Z, likely under
08 KT.

KBUR...High confidence in VFR through 09Z with seasonal southerly
winds. 20% chance of IFR conditions 10-16Z.


.MARINE...20/908 AM.

Low confidence on fog forecast, but dense fog is possible now
through the weekend. High confidence in widespread short period
seas into tonight, with decreasing heights.

High confidence in Small Craft Advisory (SCA) winds from the
Central Coast the San Nicolas Island through tonight, with weaker
and more borderline SCA over the weekend. Over the inner waters
from the Santa Barbara Channel to the San Pedro Channel, SE winds
will form each morning through at least morning, up to 15 kt
through the passages and channels. Typical onshore winds expected
in the afternoon, with near SCA west winds on the far western
Santa Barbara Channel.


PZ...Small Craft Advisory in effect from 3 PM this afternoon to 3
      AM PDT Saturday for zone 645. (See LAXMWWLOX).
     Small Craft Advisory in effect until 3 AM PDT Sunday for
      zones 670-673. (See LAXMWWLOX).
     Small Craft Advisory in effect until 3 AM PDT Saturday for
      zone 676. (See LAXMWWLOX).



No significant hazards expected.



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