Area Forecast Discussion
Issued by NWS Los Angeles, CA

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FXUS66 KLOX 191005

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
305 AM PDT Fri Apr 19 2019

.SYNOPSIS...19/254 AM.

Increasing onshore flow will knock a few degrees off of today`s
highs, but it will remain quite warm across the inland areas.
There will be a slight chance of a thunderstorm over the
mountains this afternoon. Much cooler temperatures are expected
Saturday as a robust marine layer develops.


.SHORT TERM (TDY-SUN)...19/238 AM.

The marine layer is 800 feet deep which is up from 400 feet from
last evening. This has precluded the formation of any large areas
of dense fog. There is still patchy dense fog mostly near the
foothills. Marine layer stratus will cover the coasts and some of
the lower vlys this morning. Onshore flow, onshore trends and weak
cyclonic lift will keep the stratus going through the morning and
maybe the early afternoon otherwise high level clouds will keep
things partly cloudy. There will be a great amount of cooling
along the beaches, good cooling across the rest of the coastal
areas but only a little cooling from the vlys inland. Coastal
temps will be near normal and inland temps will end up about 5
degrees above normal. There will be just enough lower-mid level
moisture interacting with weak diffluence and mtn heating to
justify a slight chc of TSTM this afternoon and early evening for
most of the area bordering Kern county (but not the Antelope Vly)
The main threat from these TSTMs would be dry lightning as well
as gusty winds.

The trof will move into the state tonight and exit the area later
Saturday. An eddy will spin up and will add to the lift of the
trof. The onshore trends will continue as well and with everything
mixed together there is a perfect recipe for a deep marine layer.
Marine layer stratus will cover all of the csts and vlys as well
as the coastal slopes. The KDAG gradient is forecast to reach 9+
MB but the afternoon.This will make it a slow to no clearing day.
MAx temps will plummet into the 60s and will end up 5 to 10
degrees below normal. The strong w to e gradient will bring
advisory level winds to the Antelope Valley.

Northwest flow will increase behind the trough Saturday and set up
a little Sundowner for srn SB County Saturday night. This may keep
the marine layer away from that area overnight but low clouds
should return elsewhere. With less of an eddy circulation Sunday
and weaker onshore flow low clouds should clear earlier with
maybe a couple degrees of warming.

.LONG TERM (MON-THU)...19/252 AM.

Both the GFS and the EC agree that there will be ridging over through
Thursday although the ridge will begin to break down on Thursday.
Yesterday`s forecast had a bigger Great Basin high than today`s
runs do and ads such there is much less (read hardly any) offshore
flow forecast for the period. Tuesday and Wednesday will still be
the warmest days will be with quite a few highs again back into
the 80s, but now any 90 degree reading looks unlikely. Better
onshore flow will cool the coasts back to near normal while the
inland areas will cool but will remain 5 to 8 degrees above



At 0540Z at KLAX, the marine layer was 300 feet deep. The top of
the inversion was 1400 feet with a temperature of 25 degrees

Moderate confidence in coastal TAFs with LIFR conds developing
between 07Z and 10Z and lasting until 15Z-17Z. Good confidence in
inland TAFs.

KLAX...moderate confidence in 00Z TAF. There is a 50% chance of
VLIFR/LIFR conditions 10Z-17Z and MVFR conditions 17Z-20Z.

KBUR...High confidence in CAVU TAF.


.MARINE...19/304 AM.

High confidence in winds staying below Small Craft Advisory (SCA)
through this afternoon, although local gusts to 20 KT are likely
in the San Pedro Channel in the afternoon hours. Moderate
confidence in dense fog with visibility under one mile becoming
more expansive this morning and possibly into this afternoon,
especially along the Los Angeles and Orange County coast lines.

West to northwest winds and short period seas will be increasing
tonight through Sunday night. There is a 40% chance that the
northern outer waters zone (PZZ670) will need a (SCA) this
evening, with much higher confidence for all outer waters likely
needing a (SCA) for gusty winds and choppy seas Saturday morning. There
is a 30 percent chance for Gale Force winds between Point
Conception and San Nicolas Island Saturday afternoon and Sunday
with Sunday looking more likely than Saturday. Otherwise,
there is an 80% chance for widespread SCA conditions across all
outer water zones with a 70% chance for (SCA) for the Santa
Barbara Inner waters (PZZ650) and lower chance (40%) for the inner
waters from Point Mugu to San Mateo Point (PZZ655)this weekend.





No significant hazards expected.



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