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000 
FXUS66 KLOX 200322
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA 
822 PM PDT Thu Apr 19 2018

.SYNOPSIS...19/722 PM.

Gusty west winds will continue across the area through early 
Friday. A ridge of high pressure will build over the region,
bringing above-normal temperatures Friday through Monday. An eddy
will usher in overnight low clouds and fog to some coastal areas
through Monday. A low pressure system approaching the area on 
Tuesday will bring a cooling trend through next Thursday.

&&

.SHORT TERM (THU-SUN)...19/742 PM.

***UPDATE***

Pretty breezy evening across the area as post-frontal winds
developed this afternoon as expected. Current observations
indicate west to northwest wind gusts generally between 30 and 
45 mph across the Ventura/Los Angeles county mountains, Antelope 
Valley and South Coast of Santa Barbara county. For these areas, 
will keep current wind advisories in effect through 300 AM Friday 
morning as winds should continue through the evening and
overnight. However, winds have diminished below advisory-levels 
across the Central Coast as well as the coastal areas of Ventura 
and Los Angeles counties. So, will let those wind advisories 
expire at 900 PM this evening. 

As for clouds, afternoon/early evening stratocumulus across inland
areas is dissipating as sun has gone down. Therefore, main cloud
concern overnight will be the potential for stratus. Latest
sounding data indicates weak marine inversion based around 1800
feet north of Point Conception and around 900 feet south of Point
Conception. Stratus is already developing around the Vandenberg
and Lompoc area this evening. So, stratus should continue to
develop overnight across the Central Coast and the Santa Ynez
Valley. South of Point Conception, northerly flow should keep
coastal Ventura county and southern Santa Barbara county 
stratus-free overngiht. However for Los Angeles county, a weak
eddy circulation is forecast which should help develop some
stratus late tonight (although confidence in that forecast is
rather low this evening). 

Overall, current forecast has good handle on the immediate short
term. Will make some minor adjustments to the forecast grids, but
nothing dramatic. 

***From Previous Discussion***

The upper low has departed and a ridge will move in tonight and
Friday and remain in place at least through early Sunday for a
warming trend, mainly inland. For today gusty west to northwest
winds that developed behind the departed cold front will continue
into the overnight hours before weakening. Coastal areas, the I5
corridor, and the Antelope Valley will bear the brunt of these
winds with not as much reaching the coastal valleys. Overall a
weaker post-frontal wind event than what we saw Monday but still
at least low end advisory for the above mentioned areas. 

Later tonight an eddy circulation is expected to develop that will
help pull in some low clouds into srn LA County. Forecast
soundings indicate just enough of an inversion below 1000' to 
support it but probably not a real solid coverage. Some low clouds
also expected to develop along parts of the Central Coast and in 
the southern Salinas Valley where there could also be some dense
fog.

With the ridge building in Friday and Saturday expecting temps
inland to jump several degrees, back up into the 80s. Coastal
areas will still have enough of an onshore flow and likely some
marine layer clouds during the morning hours at least to keep
temps quite a bit cooler there. 

A little cooling trend expected for Sunday in most areas as the
ridge shifts east and a weak trough moves into the Pac NW. Pretty
decent onshore trend by afternoon so a stronger and earlier sea 
breeze expected.

.LONG TERM (MON-THU)...19/116 PM.

Models still in a bit of flux next week with the expected
development of a cutoff low at some point several hundred miles
west of the coast. Today's GFS solution shifted to yesterday's
ECMWF, keeping the low west of 130w through at least Thursday then
slowly moving it towards the coast next weekend. Meanwhile, the
ECMWF actually did the opposite and looks a little closer to
yesterday's GFS. So not a lot of confidence especially around mid
week. Early in the week not expecting a lot of change from Sunday.
Slightly cooler perhaps with the onshore trends but heights stay
fairly high at least through Tuesday so most inland areas should
remain at least a few degrees above normal. After that it just
depends on the speed and magnitude of the upper low and where it
ends up moving inland. Can't rule out some shower chances when
that happens but right now the models are holding any of that off
until at least Friday. Likely still a lot of back and forth in the
solutions before there is any real confidence beyond early next
week.

&&

.AVIATION...19/2239Z.

At 2215Z, there was a very weak inversion at KLAX, based around 
1200 feet. The top of the inversion was 2000 feet with a 
temperature of 9 degrees Celsius.

Overall, moderate confidence in 00Z TAF package. High confidence
in VFR conditions for all sites through 10Z. From 10Z-18Z, low
confidence in coastal TAF sites as well as KPRB due to low
confidence stratus forecast. 

KLAX...Overall, moderate confidence in 00Z TAF. High confidence in
VFR conditions through 10Z. From 10Z-18Z, low confidence in
stratus forecast in terms of formation (50% chance VFR conditions
will prevail) as well as potential timing (+/- 3 hours of current
12Z forecast) and flight category (if stratus develops, potential
for MVFR to LIFR conditions).

KBUR...high confidence in 00Z TAF. There is a 20% chance of LLWS
10Z-20Z.

&&

.MARINE...19/753 PM.

High confidence in Small Craft Advisory (SCA) level winds across 
all coastal waters thru late tonight before subsiding. There is a
20-30% chance of Gale force winds at times across the southern 
outer waters this evening as well. Steep short-period seas are 
expected across the waters thru tonight. 

SCA level winds are expected across the outer water Fri afternoon
into Fri night. There is a 30-40% chance of SCA level winds 
across the northern inner waters Fri afternoon and evening, and a
20% chance of SCA level winds across the SBA Channel.

There is a 20-30% chance of SCA level winds across the outer
waters Sat through Sun. SCA level winds are likely across the
outer waters and northern inner waters Mon.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Wind Advisory in effect until 9 PM PDT this evening for zones
      34>36-51. (See LAXNPWLOX).
     Wind Advisory in effect until 3 AM PDT Friday for zones
      39>41-52>54-59-87. (See LAXNPWLOX).
PZ...Small Craft Advisory in effect until 3 AM PDT Friday for
      zones 645-650-655-670-673-676. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK (SUN-THU).

No significant hazards expected.

&&

$$

PUBLIC...MW/RAT
AVIATION...RAT

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