Scientific Forecaster Discussion
Southwest California area forecast discussion...updated
National Weather Service Los Angeles/Oxnard California
1045 PM PDT Friday Jul 3 2015
Updated aviation section
Synopsis... overnight and morning low clouds and fog are expected
through the weekend...possibly lingering at the coast...but clearing
in the valleys. Temperatures will be cooler. By midweek an upper low
pressure system will bring a deeper marine layer and more
cooling...before a weak ridge returns at the end of the week to warm
back up a few degrees.
Short term (today-mon)...evening update
Latest satellite imagery indicated mostly clear skies except for
some patchy low clouds lingering along coastal areas. Also...a line
of middle level clouds have been moving across the Antelope Valley and
the la County mountains this afternoon and evening. High temperatures were down
a few degrees near the coast...and 4 to 8 degrees in most inland
areas...except only a couple degrees for the Antelope Valley. The
combination of stronger onshore flow and drier SW flow aloft helped
to dry out the atmosphere. Therefore the humidity was nearly as
oppresive as it was over the previous week.
Synoptically...a large upper low over the eastern Pacific will
continue to push closer to California. This will allow for cooler SW
flow to become more dominant over the region while the upper high
gets pushed farther east allowing the monsoon flow to remain well
east of the area this weekend and into next week. There will be some
instability across the la/vtu County mountains this weekend...but with
limited middle level moisture to work with...expect a few flat cumulus
afternoon buildups. A strong onshore gradient expected tomorrow over
+9 mb will bring some gusty winds across the la mountains and the
Antelope Valley. There will be local gusts to 50 miles per hour around Lake
Palmdale and adjacent foothills...but not expecting widespread Wind
Advisory level winds.
The weather pattern will become more typical June like with night
through morning low clouds across the coast and some coastal valleys
through much of next week as a broad upper level trough will linger
over much of California. The latest amdar sounding near lax
indicated the marine layer was around 1100 feet deep with a strong
inversion in place. Coastal areas will likely have a tough time
clearing in the afternoons...but valleys should clear late each
morning. Expect very cool conditions across the coastal areas...and
near normal temperatures for inland areas with valley highs ranging in the
middle 80s to lower 90s...and lower to middle 90s for the Antelope Valley
***From previous discussion***
Long term (tue-fri)...minimal changes Tuesday from Monday. Models
have been consistent last few days showing that upper low getting
picked up by the westerlies and pushed into northern and central
California by around middle week. This will likely bring about a deeper
marine layer and cooler temperatures all areas Wed/Thu. By Friday the trough is
gone and weak ridging returns for a warming trend going into the
weekend. No threat of monsoon thunderstorms for the next 10 days at
least as the flow aloft is from a dry southwest direction.
At 0415z...the marine inversion at klax was 900 feet deep. The top of
the inversion was at 2500 feet with a temperature of 25 degree c.
Expect widespread LIFR to IFR conds across the coastal plain
tonight...with IFR to LIFR conds spreading into the valleys late
tonight. Skies will clear by middle morning in the valleys...and by
noon across the coastal plain...except clouds will likely linger
into the afternoon at the beaches.
Klax...moderate confidence in the 06z taf. There is a 30 percent
chance that ceilings will linger through the entire day on Sat.
Kbur...moderate to high confidence in the 06z taf. There is a 20
percent chance that conds will remain VFR through Sat evening.
There may be some local Small Craft Advisory level wind gusts across the outer waters
during the afternoon and evening hours through Sunday. There is a 20
to 30 percent chance that Small Craft Advisory level winds will become widespread
enough to require advisories during the afternoon and evening hours
each of the next three days...mainly across the southern two thirds
of the outer waters.
high rip current risk (see laxsrflox).