Scientific Forecaster Discussion
Southwest California area forecast discussion
National Weather Service Los Angeles/Oxnard California
200 PM PDT Tuesday Mar 11 2014
Offshore flow will bring gusty and potentially damaging winds to
much of the area later tonight through Wednesday afternoon. There
will also be critical fire weather conditions from Wednesday morning
to early afternoon from la to slo County. Afternoon temperatures
will remain above normal through the weekend as high pressure will
dominate our weather pattern.
Short term (today-fri)...advisory and warning level Santa Ana winds
coming in tonight and Wednesday as a trough drops through the Great
Basin. Pretty good cold air advection with this one and lax-dag
gradient around -6 mb. Taking a look at cross sections of model
output through Ventura and Los Angeles counties the NAM is
definitely the strongest showing winds between 50-55kt in the 2k-3k
feet layer. Subsidence will push these winds even lower which is why
the Santa Clarita valley has been included in the warning along with
the mountains (including the Santa monicas). Opted to keep the valleys
and coast in the advisory category, though the higher peaks above
the valleys like Wiley Ridge in Ventura County could see some
isolated gusts to around 60. Gusty easterly winds also expected to
develop across interior slo County and the Cuyama Valley, though at
this time I think most locations will remain below advisory levels.
Forecasting daytime temperatures with these strong cold advection
cases is always a bit tricky but typically they end up being not
quite as warm as we expected. I think actually the MOS guidance
numbers have a decent handle on the highs for Wednesday with the coastal
areas definitely the warmest, topping out around 80, then cooler for
the valleys and even cooler for the mountains and Antelope Valley.
This is a pretty brief event as winds should drop below advisory
levels by afternoon. There's a little resurgence Thursday morning but
below advisory levels. By Thursday afternoon most areas should be seeing
their normal afternoon sea breezes. Again a bit tricky with the
highs due to the onshore trends in the afternoon, but overall
interior areas should warm several degrees while coastal areas
either stay about the same or possibly cool a degree or two. Not
much change Fri, though even less morning wind and probably a bit of
coastal cooling due to an earlier onset of the sea breeze.
Long term (sat-tue)...strong high pressure returns to California
over the weekend. This will be coupled with a light offshore
gradient as a trough moves through UT/co. This is a bit too far east
to really get the strong offshore gradients, but enough to further
warm up an already very warm air mass with the 585mb high near pt
Conception by Sunday afternoon. So we could be looking at some more
record highs this weekend, especially by Sunday with valleys into
the lower 90s and coastal areas in the middle to high 80s. Still pretty
strong high pressure on Monday, though flattening out some as a
system moves into the eastern Pacific. Gradients will also start
trending onshore so most areas will see an earlier sea breeze which
will cap highs somewhat lower than Sunday. Similar trends Tuesday.
The new European model (ecmwf) is a bit more agressive with that system moving it
into northern California Tuesday afternoon while the GFS still has weak
ridging over California, especially the southern part. So forecast temperatures
may need additional cooling but either way still above normal.
VFR conditions will continue through Wednesday. Ksbp will continue
to struggle with low level wind shear for a couple of hours.
Otherwise...low level wind shear will be the primary concern along
with gusty winds and turbulence through Wednesday. The low level
wind ahear will Transfer to kbur and kvny tonight into Wednesday.
Klax...good confidence in VFR conditions through Wednesday. There is
a 20 percent chance of low level wind shear on Wednesday.
Kbur...good confidence in VFR conditions through Wednesday. There is
a 20 percent chance that there will not be low level wind shear on
moderate to strong offshore winds will form by Wednesday over Los
Angeles and Ventura counties...as well as interior Santa Barbara and
San Luis Obispo counties. Elevated fire concerns will exist today.
As the winds increase tonight into Wednesday...cold air from the low
will bring increased humidities...especially in the
mountains...which will take time to lower through the day on
Wednesday...first near the coast early Wednesday morning...then up
through the higher elevations in the afternoon. Despite the higher
humidities...sustained winds around 40 miles per hour and gusts around 65 miles per hour
are likely during the peak on Wednesday over Los Angeles and Ventura
counties...which would create an environment favorable for extreme
fire behavior if a fire starts. These winds will push into interior
San Luis Obispo and Santa Barbara counties as well. A red flag
warning will be issued for Los Angeles and Ventura counties as well
as the interior portions.
Weaker but still gusty northeast winds will continue Wednesday night
through Thursday...with elevated fire concerns.
High Wind Warning (see laxnpwlox).
Red flag warning (see laxrfwlox).
Wind Advisory (see laxnpwlox).
Small Craft Advisory (see laxmwwlox).
Marine weather statement (see laxmwslox).