Scientific Forecaster Discussion
Southwest California area forecast discussion...updated
National Weather Service Los Angeles/Oxnard California
1005 PM PST Thursday Mar 5 2015
Updated aviation section
A large high will persist into early next week with fair skies and
above normal temperatures through early next week. Cooling trend with
increasing clouds expected to begin by the middle of next week as a
low pressure system approaches the coast.
Short term (tonight-sun)...upper level ridge of high pressure
building over northern and central California tonight into Friday
while upper low spins across Baja California. This developing pattern will set
up a slightly stronger upper level wind support for Southern
California. In addition...the surface offshore gradients are also
expected to be slightly stronger on Friday as compared to the last
couple of days. Taking a look at the current pressure
gradients...already seeing evidence of this offshore trend as
lax-Daggett currently at -3.3 mb compared to -2.4 mb 24 hours ago.
The 00z NAM projects the lax-Daggett gradient to be in the -5.0 to
-5.5 mb range by Friday morning. With this in mind...have posted a
low-end Wind Advisory for the mountains taking effect
immediately...as well as the Santa Clarita valley and Ventura
valleys valid 6 am Friday. Already seeing some winds gusting over 40
miles per hour this evening across the Santa Monica Mountains. Wind gusts are
expected to reach 45 miles per hour across the mountains...and 35 to 40 miles per hour in
favored valley locations. The offshore winds are also expected to
make a slightly stronger push into the coastal areas of Ventura
County and around Malibu on Friday morning but should mostly remain
below advisory levels.
The stronger offshore flow and increasing boundary layer temperatures
should result in a good 3 to 6 degrees of warming for much of the
region on Friday. As a result...warmest coastal and valley areas are
expected to climb into the lower to middle 80s on Friday...which is
10-15 degrees above normal for this time of year. Offshore flow will
continue to bring these very warm temperatures into the weekend.
*** From previous discussion ***
Long term (mon-thu)...the little inside trough that brings a brief
onshore flow return Sunday will shift east Monday with the ridge
re-strengthening late Monday and Tuesday. So after a bit of a "cool
down" late in the weekend temperatures should again trend warmer Monday/Tue,
possibly close to 90 in some of the warmer valleys which would be a
good 20 degrees above normal. Then turning cooler Wednesday/Thursday as the
ridge breaks down and a weak trough moves into northern California. We'll
see a big increase in high clouds with this as early as late Tuesday
but it's not looking real good for rain this far south. Somewhat
better chances north of pt Conception but even there any amounts
would be insignificant. The ridge returns quickly after that for a
warming trend going into next weekend.
At 0550z...there was no marine layer at klax.
VFR conditions expected through period...except a ten percent chance
of vlifr/LIFR conditions at kprb between 11z-15z. Otherwise...
offshore flow will bring a chance of moderate low-level wind shear
and turbulence across portions of Ventura and Los Angeles counties
Klax...VFR conditions are expected throughout the period. Any east
winds will likely remain below 5 knots.
Kbur...VFR conditions are expected throughout the period. There is a
30 percent chance of moderate low-level wind shear and turbulence
between 15z and 20z on Friday.
Weak to locally moderate northerly flow across the region through
Friday with weak northeast flow near the immediate coastline. Flow
will be locally moderate at times along the portions of the Ventura
and Los Angeles County coastline affected by Santa Ana winds.
Northwest winds will increase over the outer waters on Saturday and
Sunday and there is a twenty percent chance they may reach Small
Craft Advisory thresholds.
Wind Advisory (see laxnpwlox).
High rip current risk (see laxsrflox).