Scientific Forecaster Discussion
Southwest California area forecast discussion
National Weather Service Los Angeles/Oxnard California
200 PM PDT Sat Jul 4 2015
there will be night through morning low clouds and fog in coastal
and some valley areas through early next week...with temperatures
near to slightly above normal. Low pressure will bring a deeper
marine layer Wednesday through Friday...with more extensive night
through morning low clouds and fog west of the mountains... and
slightly below normal temperatures in most areas.
Short term (tonight-tue)...the large scale pattern consists of a
high amplitude ridge centered in the Gulf of Alaska undercut by a
weak closed low west of Point Conception...with another high
centered over the 4-corners area. A dry southwest flow continues
aloft with onshore gradients at the surface.
Low clouds continue to linger near many coastal areas this
afternoon...and expect some locations to retain partly cloudy
conditions through the day. Afternoon temperatures so far have
fallen around 2-5 degrees compared to friday's highs. Onshore
gradients will help to keep low clouds near the coast...and produce
gusty southwest to westerly winds through the mountain passes into
the Antelope Valley. Visible satellite shows some cumulus
development over the San Gabriel and Ventura mountains. Expect an
early return of the marine layer low clouds and fog for the
overnight period...and with good onshore gradients expect the inland
push to be more complete...covering all of the coastal valleys
tonight into early Sunday.
The upper low will remain stationary through Sunday...then drift
very slowly to the northeast through Tuesday. Meanwhile the 4-
corners high will slowly shift south. Daytime high temperatures will
subside a few degrees in the deserts...but otherwise change little
through the short term. Overnight to morning low clouds and fog will
continue each day...covering the coast and coastal valleys.
Long term (wed-sat)...the upper low will shift slowly eastward on
Wednesday...pushing onshore over the Bay area Thursday and then
lifting to the northeast more rapidly Friday into Saturday. The main
effect over southwest California will be to further deepen the
marine layer so that it will extend over the inland valleys and the
lower coastal mountain slopes. Some drizzle may also be possible as
this occurs. A slow cooling trend will also occur through Friday.
At 1626z...the marine inversion at klax was based at 2200 feet. The
top of the inversion was 4300 feet with a temperature of 23 degrees
Overall...moderate confidence in 18z taf package. Stratus is
dissipating at expected...although immediate coastal
areas...especially south of Point Conception...will likely remain
scattered-broken through the afternoon. For tonight...expect stratus to move
inland overnight...pushing into the coastal valleys with MVFR/IFR
ceilings likely at all coastal/valley taf sites.
Klax...low confidence in 18z taf. There is a 50% chance that MVFR
ceilings will not scatter out this afternoon. For tonight...high
confidence in return of ceilings...but only moderate confidence in
flight category (cigs could remain at MVFR levels overnight).
Kbur...moderate confidence in 18z taf. High confidence in VFR conds
through this evening. Overnight...high confidence in return of IFR ceilings
but low confidence in timing (+/- 2 hours of current 08z forecast).
For the outer waters...high confidence in west to northwest winds
remaining below Small Craft Advisory levels through Sunday night
(although there may be some local gusts to 25 knots in the afternoon
and evening hours). For Monday through Wednesday...the winds will
increase a bit...and there is a good chance of Small Craft Advisory
For the inner waters...high confidence in westerly winds remaining
below Small Craft Advisory levels through Sunday. From Monday
through Wednesday...the winds will increase a bit. There is a slight
chance of Small Craft Advisory level gusts across western sections
each afternoon and evening.