Scientific Forecaster Discussion
Southwest California area forecast discussion...updated
National Weather Service Los Angeles/Oxnard California
425 am PDT Friday Oct 24 2014
Updated aviation section
Another warm and dry day is expected today. On Saturday...the
remnants of a weak front will sweep across the area...bringing much
cooler conditions and the chance of some light rain over the central
coast. Cool conditions will continue on Sunday...then offshore flow
will develop the first half of next week...bringing warmer
temperatures to the area.
Short term (today-sun)...overall...00z models are in very good
synoptic agreement through the period. At upper levels...ridge will
begin to weaken today...then a trough will move across the West
Coast Saturday/Sunday. Near the surface...onshore flow will
gradually strengthen through the period.
Forecast-wise...not much change from previous thinking. Main
forecast "concern" will be the rain chances for the central coast on
Saturday. All models still indicate the dying remnants of a cold
front will sweep across the central coast late Saturday morning and
afternoon. Based on moisture/quantitative precipitation forecast forecasts...a slight chance of showers
is still warranted and will be left in the forecast. Any showers
that do develop on Saturday will be very light...and not of any
Otherwise...secondary issue will be the marine layer stratus. For
this morning...stratus/dense fog has returned to the central
coast...and some very patchy stratus is trying to develop along the
Los Angeles County coast. For tonight/Saturday morning...with
approaching trough and increase in onshore flow...marine layer
stratus should be more widespread...impacting the coastal plain
south of Point Conception (and potentially extending into the
valleys). For Saturday night/Sunday...northerly flow behind the
front will limit the stratus west of the mountains to Ventura and
Los Angeles counties. However...the northerly flow should result in
widespread cloud cover across interior slo/sba counties as well as
the northern mountain slopes (with even the possibility of some
light showers on the north slopes Sunday morning).
As for temperatures...today will be slightly cooler...then more
dramatic cooling Saturday/Sunday.
As for winds...major issue will be the northerly winds late Saturday
night and Sunday across the Santa Ynez range and I-5 corridor. At
this time...moderately confident that winds will reach advisory
levels and the situation will need to be monitored closely.
Long term (mon-thu)...for the extended...models continue to exhibit
good synoptic agreement through Wednesday...then begin to diverge a
bit on Thursday. At upper levels...models agree ridge will build
over the area Monday through Wednesday (with the European model (ecmwf) stronger with
the ridge)...but by Thursday the European model (ecmwf) maintains the ridge while the
GFS is more pronounced with an approaching trough. Near the surface
weak offshore flow will prevail Monday through Wednesday...then some
onshore flow may return on Thursday (if the GFS is correct).
Forecast-wise...Monday through Wednesday will be very nice with
warming temperatures and little...if any...marine layer stratus as
ridge builds overhead and weak offshore flow develops. Do not
anticipate any significant offshore winds through the period...just
some locally gusty northeasterly winds in the more wind-prone area.
On Thursday...the GFS would indicate a noticeable cooling trend for
the entire area as a front approaches the areas. On the other hand
the European model (ecmwf) maintains the ridge and keep the front further offshore.
At this time...will lean the forecast to the European model (ecmwf)...keeping the
previous thinking of just some very slight cooling Thursday
A bit further out for Halloween...the GFS actually indicates the
potential for some decent rain while the European model (ecmwf) is dry. Still too
early to "bite" on the GFS solution...but it will have to be watched
Aviation...24/1130z...the base of the inversion at klax at 1115z
was near the surface. The inversion top was at 2200 feet with a
temperature of 24 degrees c.
Expect VFR conds this morning...except for LIFR to vlifr conds
across portions of the central coast through middle morning. There is
a chance of brief IFR conds across coastal sections of l.A, County
through middle morning. Expect more widespread stratus tonight/Sat
morning...with IFR to LIFR conds in most coastal areas. Valleys should
Klax...moderate confidence in the 12z taf. There is a 20 to 30
percent chance of IFR conds between 12z and 16z. There is a 20
percent chance that IFR ceilings will not arrive until 11z Sat morning.
Kbur...high confidence in the 12z taf with VFR conditions expected
through the period.
northwest winds are expected to increase late Sat night and sun. Small Craft Advisory conds
are nearly certain across the outer waters by Sunday...and there is
a decent chance of gale force winds Sun afternoon into Sun night
from Point Piedras Blancas to Point Sal from 10 to 60 nm off
the coast...and from Point Sal to near San Nicolas Island.
Hazardous sea conds are also possible across much of the outer
waters by late Saturday night and persist through Monday.
marine weather statement (see laxmwslox).