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Area Forecast Discussion (AFD)

Issued by Los Angeles, CA (LOX)

FXUS66 KLOX 230729

Area Forecast Discussion...UPDATED
National Weather Service Los Angeles/Oxnard CA 
1229 AM PDT Mon Apr 23 2018

.SYNOPSIS...22/901 PM.

There will be overnight and morning coastal low clouds and fog 
for several days this coming week otherwise conditions will be 
warm and dry. Temperatures will cool a bit Friday and Saturday as
a weak weather system moves across the region.


.SHORT TERM (MON-THU)...22/900 PM.

Weak upper-level ridging remains over the area this evening and
will continue to linger into Monday. Despite 500 mb heights
climbing slightly, onshore flow is progged to and is strengthening
tonight as southwest flow aloft establishes. 950 mb temperatures
should cool slightly and allowing for a cooling trend to continue
into Monday. Ridging aloft will gradually break down through
Monday night. A disturbance near 40N and 150W is slated to break
off of a trough in the Gulf of Alaska Monday, then this trough 
will slowly move towards the California Coast through late this 

Onshore flow should gradually increase through this week,
continuing a cooling trend and a more persistent marine layer and
better organized marine layer stratus. A shallow marine layer
depth this evening could bring patchy dense fog to the coast 
tonight, but the marine layer depth should deepen overnight 
allowing for less dense fog on Monday morning. Some intrusion is
possible into the lower valley areas late tonight and early
Monday morning.


.LONG TERM (FRI-MON)...22/125 PM.

Large upper level low pressure system will be spinning off the
northern California coast by Thursday. Latest 12z GFS model
trending further northward (similar to ECMWF model) with moving
this low pressure system inland Friday night into Saturday. 
As a result, keeping Pops below 15 percent in the Friday
night/Saturday time frame seems reasonable for now across our 
area, as most of the moisture and energy with this system is
projected to remain well north. Also of note, the latest GFS
ensembles also trending much drier with this system for our
area. The main impact of this system will be gusty west to
northwest winds across the region along with a cooling trend.



At 06Z at KLAX, the marine layer was 700 feet deep. The top of 
the inversion was near 2400 feet with a temperature near 23 C,

Low confidence in coastal TAF (high confidence in the inland TAFs)
At the coast stratus will form haphazardly. There is a 30 percent
chc of 1/4SM FG from 10Z-16Z at all coastal sites. Cigs and Vis
may bounce between LIFR and IFR levels. There is a 20 percent chc
of no clearing at all.

KLAX...low confidence in TAF. There is a 30 percent chc of 1/4SM
FG from 10Z-16Z. Cigs and Vis may bounce between LIFR and IFR 
levels. There is a 20 percent chc of no afternoon clearing.

KBUR...Good confidence in the TAF, except for a 20 percent chance
of MVFR visibility between 12Z and 16Z.


.MARINE...22/742 PM.

Generally high confidence in the current forecast. Gusty NW winds
to Small Craft Advisory (SCA) level are expected over outer water
zone PZZ670 through late tonight. Otherwise, winds and seas are 
expected to remain largely below Small Craft Advisory (SCA) levels
tonight through Thursday across the Coastal Waters. There is a 
50%-60% chance of SCA winds developing on Fri for much of the 
coastal waters.

A shallow marine inversion may generate some patchy dense fog 
later tonight into Monday morning across the Coastal Waters.


PZ...Small Craft Advisory in effect until 3 AM PDT early this
      morning for zone 670. (See LAXMWWLOX).



No significant hazards expected.