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Area Forecast Discussion (AFD)

Issued by Los Angeles, CA (LOX)

FXUS66 KLOX 190340

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA 
840 PM PDT Tue Jun 18 2019

.SYNOPSIS...18/814 PM.

For the rest of the week, onshore winds will keep thick clouds 
over coastal areas. These clouds will push into the valleys 
overnight, with patchy fog and possible drizzle by morning.
Temperatures will trend cooler into Friday, and warming more by
the weekend as clouds dimish.


.SHORT TERM (TUE-FRI)...18/839 PM.

A weak offshore wind influence along with rising heights allowed
for better clearing today across the valleys, with triple digit 
heat in the Antelope Valley. However, June gloom was in full swing
once again, with low clouds lingering across many coastal areas 
through the day. ACARS soundings and Vandenberg sounding showing 
marine layer depth around 2500 feet this evening, down slightly 
from this time yesterday. Satellite imagery showing low clouds 
surging inland quickly once again this evening, already reaching 
some of the coastal valleys. 

There were a few cloud build-ups over the local mountains and
deserts this afternoon, but all thunderstorm activity remained
to the north in Kern county. While there continues to be
instability across the mountains and deserts on Wednesday
afternoon, only expecting some cloud build-ups once again
due to limited moisture and upper level ridging. 

Despite the upper level ridge of high pressure building in from
the west, onshore flow expected to be slightly stronger on 
Wednesday, with low clouds likely surging inland into the
Santa Clarita Valley and little to no clearing across coastal
areas in the afternoon hours. Little change in temperatures
on Wednesday, then a cooling trend on Thursday as the next
upper level trough moves into northern and central California. 
This system will likely deepen up the marine layer to around 
3500 feet by Thursday morning, with low clouds and fog surging
into the lower coastal slopes. This deepening of the marine layer
could bring some patchy drizzle to the region on Thursday
morning, along with less clearing for coastal/valley areas
in the afternoon hours. As a result, look for additional cooling
in all areas on Thursday. Also of note, the stronger onshore flow
combined with some upper level onshore wind support will generate
stronger onshore winds in the Antelope Valley on Thursday, with
advisory level gusts up to 45 mph possible in the afternoon
and evening hours (with isolated gusts to 55 mph possible in the
foothills). In fact, the LAX-Daggett gradient could peak over +10
mb onshore on Thursday. The strong onshore wind pattern will 
bring elevated fire weather conditions to the Antelope Valley on 
Thursday, continuing into Friday. 

The very strong onshore pressure gradients continue into Friday. 
The high pressure will recede and a little trof moves southwest 
out of Nevada and over LA county. This trof will interact with the
marine layer and the onshore flow and probably produce some 
drizzle over the coasts and valleys of LA county. The trof will 
bring lower heights which will lead to more cooling. Friday will 
be the coolest day of the next 7 with max temps 10 to 15 degrees 
below normal.

.LONG TERM (SAT-TUE)...18/205 PM.

Very weak ridging is expected over the weekend along with offshore
trends - both of which will help the marine layer clouds clear 
earlier and allow afternoon high temperatures to rise. By Sunday,
temperatures will be near normal across the interior but will 
still be 5 to 10 degrees below normal across the coasts and

Another trof will arrive Monday, this time from the northwest,
bringing back the strong onshore flow, less clearing and cooler 
coastal temperatures.



At 1731Z, the marine layer depth was around 2400 feet deep at 
KLAX. The top of the inversion was near 4300 feet with a 
temperature of 24 degrees Celsius.

Moderate confidence in the current forecast. Higher confidence in
categories, less confidence in timing. Expecting low clouds 
to be extensive overnight into Wednesday morning across
coastal/valley areas. With strong onshore flow expected on 
Wednesday, look for little to no clearing across portions of the
coast including KLAX, KSMO, KOXR, KCMA, and KSBA. 

KLAX...MVFR cigs are generally expected at KLAX through the
period. There is a 30 percent chance of brief clearing late
Wednesday afternoon/early evening. 

KBUR...MVFR cigs expected to develop overnight into Wednesday
morning, otherwise VFR conditions. There is a 20 percent chance 
of IFR cigs during this time.


.MARINE...18/812 PM.

Winds and seas will likely remain below Small Craft Advisory 
(SCA) levels through at least Thursday. There is a 30 percent 
chance for advisory level seas and winds across the outer water 
for Friday and through the weekend.





No significant hazards expected.