Scientific Forecaster Discussion
Southwest California area forecast discussion...updated
National Weather Service Los Angeles/Oxnard California
1020 PM PDT sun Jul 5 2015
..updated aviation discussion...
Upper level low pressure off the coast will maintain strong onshore
flow through the middle of the week...with extensive night through
morning low clouds and patchy fog. Below normal temperatures are
expected for the entire region by middle week...as the upper low moves
through between Wednesday and Friday. Slight warming is likely by
next weekend...but temperatures will remain slightly below normal.
Short term (today-wed)...evening update
Except for a few exceptions along the coast...high temperatures trended
down 4 to 8 degrees in most areas away from the coast today. Latest
Sat imagery indicated low clouds already pushing inland across Los
Angeles and Ventura County coastal areas and into the western
portion of the Ventura County valleys. There were also some spots
with low clouds north of Point Conception including Morro Bay...Los Osos
as well as most of the Santa Barbara central coast. The Santa
Barbara South Coast remains clear this evening. Low clouds will
spread inland overnight across all coast and valleys up to the
coastal slopes of the la/vtu County mountains overnight. The latest amdar
sounding near lax indicated the marine layer was around 1900 feet
deep...and the marine layer will likely deepen further to around
3000 feet by Monday morning.
Synoptically...the upper low situated over the eastern Pacific will
begin to draw a bit closer to California. This will help heights and
thickness levels lower a tad. However...some 950 mb boundary layer
temperatures will be a few degrees warmer well inland. This is in response
to a weaker onshore flow. Overall high temperatures will be fairly similar
to today's highs with a few exceptions. Paso Robles could see a few
degrees of warming however tomorrow...but still in the middle to upper
80s. The upper low will continue to linger just off the coast on
Tuesday before sagging slightly southeast over the socal bight and
sba/vtu counties on Wednesday.
With the low moving closer to the forecast area...low clouds will
deepen further and it looks like there will be enough lift to cause
some drizzle to be squeezed out of the stable marine layer for
la/vtu/sba counties west of the mountains both Tuesday and Wednesday mornings.
Will brief the middle shift to possibly add drizzle into the forecast.
Overall...expect cooler than normal conditions over the next 5 days
as the upper low moves over the region on Thursday. Was looking at some
convective parameters as the upper low moves overhead on Thursday
afternoon. 500 mb temperatures are forecast to be around -14 degrees c.
Although convective parameters are not too impressive at this
point...would not be surprised if an isolated thunderstorm developed
near the core of the low. Another upper trough develops once the
upper low fills in and pushes east.
***From previous discussion***
Long term (thu-sun)...models in pretty good agreement in the Long
Run...with the European being a bit slower in moving the low and
less wet throughout. Tending to the GFS solution as it has been
the better performer so far this Summer. The upper low should track
into slo County on Thursday. The marine layer will remain
deep...with night through morning clouds to the coastal slopes and some
drizzle possible. There may only be partial clearing west of the
mountains on Thursday. No probability of precipitation in the forecast...but would not be
surprised if there is some trace precipitation in some areas on
Thursday...particularly across slo and sba counties and in the
foothills of l.A. County. Maximum temperatures should be down a couple of
degrees...with temperatures generally well below normal for July. The upper
low will center over our area Thursday night and Friday and a trough
will remain west of the region through Sunday even after the low
moves on to the east on Saturday. Expect the marine layer to remain
fairly deep...and any warming to be limited. Heights will rise
across the region on Sat and sun as a strong upper high over the
south-central US expands westward. This should bring some decrease
in the marine layer depth...a reduction in night through morning
stratus in the valleys...and some warming to most areas on Sat and
At 0352z the marine inversion at klax was based at 2200 feet. The
top of the inversion was at 4500 feet with a temperature of 23
Expect widespread IFR conds tonight and Monday morning...except local
MVFR conds in coastal sections...especially S of pt Conception. Slow
clearing expected on Monday...with clouds possibly lingering through
the day at the beaches S of pt Conception.
Klax...moderate confidence in the 06z taf. There is a 20 percent
chance of IFR conds between 09z and 15z. There is a 20 to 30 percent
chance that ceilings will scatter out between 20z Monday and 02z Tuesday.
Kbur...moderate confidence in the 06z taf. There is a 20 to 30
percent chance ceilings will remain in the MVFR category overnight.
For the outer waters...high confidence in west to northwest winds
remaining below Small Craft Advisory levels through Monday morning.
However winds become northwest dominant and do increase across the outer
waters Monday afternoon through early Wednesday morning. High
confidence that Small Craft Advisory conditions will develop Monday
late afternoon through early Wednesday morning.
For the inner waters...high confidence in westerly winds remaining
below Small Craft Advisory levels through Monday. Winds will
increase some starting Monday night. There will be Small Craft
Advisory level gusts across western sections each afternoon and
evening through Thursday...and there is a chance the gusts could be
widespread enough for an advisory.