Southwest California area forecast discussion
National Weather Service Los Angeles/Oxnard California
944 PM PDT Tuesday Jun 18 2013
Synopsis...
A northerly pressure difference across the state will create gusty
winds across portion of southwest California through Wednesday. The
temperatures should be about normal into next week as the southern
portion of a large low system will linger over the region. The
center of the low will slowly move northeast over the weekend for
an increase in the night to morning marine layer early next week.
&&
Update...
Ksba-ksmx surface gradients hover near -6 mb this evening.
Verification of the High Wind Warning has already occurred with
Gaviota sensors recording gusts up to 61 miles per hour and sustained winds
greater than 40 miles per hour. The Las Flores Canyon sensor also have
recorded sustained winds greater than 40 miles per hour. A Wind Advisory was
also added for the Ventura County mountains...and the Santa
Clarita and San Fernando Valley. NAM-WRF and local 4-km WRF
solutions continue to expand the northerly wind push hinted at
earlier in 12z and 18z local 4-km WRF solutions. With NAM-WRF and
local 4-km solution performing well with the wind the package was
trended this direction.
&&
Previous discussion...
Short term...advisory threshold winds will likely return again
Wednesday evening but slightly weaker than tonight as the thermal
trough over the bight begins to surge north and air modifies along
the central coast. Guidance was consistent with previous runs and
a warming trend is likely at the coast and cooling trend inland
Wednesday as the trough gradually shifts over interior California.
A warming trend is likely over the entire area Thursday though
temperatures will remain a few degrees below normal. Slight
temperatures changes are expected Friday...the trend will reverse
and cool at the coast and warm inland by a couple of degrees.
Long term...a surface ridge of high pressure is expected to
weaken over the eastern Pacific Monday through Tuesday. Until then
a moderate to strong onshore pressure gradient will continue near
shore and cause an unorganized low level cloud field within the
marine layer. The bulk of the cloudiness may occur over the Los
Angeles basin during the night and morning periods and over
portion along the central coast. As the ridge weakens the onshore
gradient will become weak to moderate and low level cloudiness may
become organized. Little changes are expected in temperatures with
slightly below seasonal normals at the coast and slightly above
normal inland are likely through the period.
&&
Fire weather...
Increasing northwest to north flow will develop across the Santa
Barbara County mountains and South Coast...as well as the Interstate
5 corridor and Antelope Valley. Gusty sundowner winds will affect
the Santa Barbara County mountains and South Coast...strongest
during the late afternoon and nighttime hours. Wind gusts between 35
and 45 miles per hour will be common with isolated gusts to 50 miles per hour. Humidities
are generally expected to remain above 20 percent with tonight's
sundowner wind event. Gusty northwest winds will also impact the
Antelope Valley as well as the mountains of Los Angeles and Ventura
counties...especially near the Interstate 5 corridor. These areas
will generally see gusts in the 35 to 45 miles per hour range with isolated
gusts over 50 miles per hour near Whitaker Peak.
On Wednesday and early Thursday...a drier air mass is forecasted to
surge into inland portions of the forecast area. During this time...there
will likely be a prolonged period of humidities in the teens and
single digits across the mountains. These very low humidities coupled with
the continued gusty north winds and very dry fuels will likely bring
a period of critical fire weather conditions in the mountains. As a
result...a red flag warning is in effect for the mountains of Los
Angeles...Ventura...and Santa Barbara counties...including the foothills
of the Santa Ynez range. This warning is valid Wednesday morning
through Thursday morning. Brief critical fire weather conditions are
also expected across the Santa Barbara South Coast and western
portions of the Antelope Valley...but durations do not appear to be
sufficiently long for red flag warnings at this time.
&&
Aviation...19/0500z.
VFR conditions will persist at most terminals except for IFR to
MVFR conditions likely at central coast and Los Angeles County
coastal terminals between 10z and 16z. VFR conditions should
redevelop between 15z and 16z.
Klax...VFR conditions will persist through at least 10z...then
there is a 70 percent chance of IFR to MVFR conditions through
16z. There is a 30 percent chance of
Kbur...VFR conditions are expected throughout the period.
&&
Lox watches/warnings/advisories...
red flag warning (see laxrfwlox).
High Wind Warning (see laxnpwlox).
Gale Warning (see laxmwwlox).
Wind Advisory (see laxnpwlox).
Small Craft Advisory (see laxmwwlox).
High rip current risk (see laxsrflox).
&&
$$
Public...Hall
aviation...Hall
fire weather...gomberg
synopsis...seto
Www.Weather.Gov/losangeles
