Scientific Forecaster Discussion
Southwest California area forecast discussion
National Weather Service Los Angeles/Oxnard California
400 PM PDT sun Apr 26 2015
..updated aviation discussion...
Gusty northerly winds will shift to the northeast late tonight into
Monday...bringing a warming and drying trend to the region through
Tuesday. The last half of the week will have a cooling trend with
increasing marine layer clouds as a low approaches.
Short term (tonight-wed)...
upper level ridge of high pressure building across the eastern
Pacific combined with weakening onshore flow has brought a warming
and drying trend to Southern California today. Temperatures will
climb to around 80 degrees today in warmest valley locations.
Another surge of northerly winds are expected to pick up this
evening. Wind advisories posted for these northerly winds include the
Santa Ynez Mountains and sba South Coast...with Montecito hills
likely having the strongest winds with gusts up to 55 miles per hour. Have also
included a Wind Advisory for this evening for the I-5 corridor in the
la/Ventura County mountains along with the Santa Clarita valley where
gusts between 40 and 50 miles per hour can be expected.
The northerly winds will shift to northeast after midnight across the
mountains...with the Santa Ana winds then descending into the valleys
and coastal areas late tonight into Monday morning. The projected
offshore pressure gradient between lax-Daggett is not all that
impressive...forecasted to be around -3.5 to -4 mb by Monday
morning. However...models continue to ramp up the upper level wind
support...with 850 mb winds now projected to be as high as 50 to 55
knots across typical wind corridors in la County. With this in
mind...wind advisories have been posted for much of Los Angeles and
Ventura counties. The focus of the strongest winds will be the Los
Angeles County mountains late tonight through middle morning Monday...
with isolated gusts as high as 60 miles per hour. Coastal and valley areas will
generally see wind gusts between 30 and 50 miles per hour. Significant warming
and drying will take place on Monday with the gusty Santa Ana winds.
Warmest coastal/valley locations expected to climb to around 90
degrees on Monday. The combination of gusty Santa Ana winds...low
humidities...warm temperatures...and drying fuels will bring elevated
fire potential for Los Angeles and Ventura counties on Monday. Please
see fire discussion below for more details.
Upper level offshore wind support will weaken significantly by Monday
night...resulting in just some light offshore breezes continuing into
Tuesday morning. Continued very warm and dry conditions on Tuesday. In
fact...some interior sections will actually be warmer on Tuesday as
compared to Monday...especially the mountains and Antelope Valley.
Most areas should then cool a couple of degrees on Wednesday.
Long term (thu-sun)...
weak upper level trough will prevail during extended period...which
will help to reinforce stronger onshore flow along with a marine layer
influence. Initially...the low clouds and fog should be confined to
mostly coastal areas on Thursday and Friday morning...then spread
inland into the valleys over the weekend. Temperatures are expected
to gradually cool during the extended period.
At 2226z...the marine inversion at klax was based at 2300 feet. The
top of the inversion was 3400 feet with a temperature of 15 degrees
Overall...high confidence in 00z taf package. With strengthening
north to northeast flow...all sites are anticipated to remain VFR
through the taf period. This evening through early Monday
morning..gusty north winds will impact the Santa Ynez range with light
low level wind shear/turbulence at ksba as well as light to MDT low level wind shear/turbulence in the
Ventura/la mountains. Early Monday morning...the flow will turn
northeast with gusty northeast winds expected at koxr as well as
kwjf/kpmd. For kbur/kvny...light to MDT low level wind shear/turbulence will be likely
Klax...high confidence in 00z taf. VFR conds are anticipated through
the taf period. There is a chance of some light low level wind shear 12z-22z due to
Kbur...high confidence in 00z taf. VFR conds are anticipated through
the taf period. Light to MDT low level wind shear/turbulence likely 08z-22z.
It is likely northwest winds will increase and gale force gusts will
exist from Piedras Blancas to San Clemente Island through late
tonight. Small Craft Advisory conditions will likely exist 0-10 nm slo County as well
as in Santa Barbara basin to San Pedro basin this afternoon through
late tonight. Steep combined seas will build to 9 to 13 feet in the
outer waters and 6 to 9 feet in the near shore basins this afternoon
and subside Monday morning. Otherwise northwest winds are expected
to increase Tuesday and there is a chance Small Craft Advisory conditions will exist
from the vicinity of San Miguel Island to Piedras Blancas Tuesday
afternoon through Wednesday evening. A low pressure system moving
east over the South Pacific and was southeast of New Zealand this
morning will continue to generate storm force winds through Monday
morning. The highest seas will propagate toward South America as the
wind fetch area is oriented west-east but a south swell originating
from this storm are expected to arrive Saturday.
Fire weather...26/1015 am
northerly winds will be on the increase once again this evening for
the sba South Coast and Santa Ynez range...as well as the Interstate
5 corridor extending from the la County mountains southward into the
Santa Clarita valley. Humidity values will generally remain above 30
percent during the evening hours. Winds will shift to the northeast
and increase in speed overnight into Monday morning. The strongest
surge of winds in the la/Ventura County mountains is expected to
occur between 2 am and 10 am on Monday...when gusts between 50 and
60 miles per hour will likely occur. For the valleys and coastal areas...the
strongest winds will likely occur between 4 am and noon...when gusts
between 30 and 50 miles per hour are expected. Humidity values are expected to
lower into the teens by middle to late morning on Monday...with some
single digit reading by afternoon. Temperatures will climb into the
80s across much of the district...with warmest coastal/valley
locations around 90 degrees. The combination of gusty Santa Ana
winds...low humidities...and warm temperatures...and drying fuels
will bring elevated fire danger to Los Angeles and Ventura counties
on Monday. There will also likely be a brief period of critical fire
weather conditions from middle morning Monday through early
afternoon...but durations are not sufficiently long to warrant a red
Wind Advisory (see laxnpwlox).
Gale Warning (see laxmwwlox).
Small Craft Advisory (see laxmwwlox).