Southwest California area forecast discussion
National Weather Service Los Angeles/Oxnard California
250 PM PDT Tuesday Jun 18 2013
..updated fire weather discussion...
Synopsis...
Gusty northerly winds are expected at times for the mountains and
the foothills of the Santa Barbara South Coast through Wednesday
night...especially during the evening hours. Temperatures will
remain near normal through middle week...followed by a slight warm up
into next weekend as the upper low currently off the Washington
coast shifts eastward. Areas of night through morning low clouds and
fog will continue for parts of the coastal plain into the weekend.
&&
Short term (tonight-fri)...have issued a Wind Advisory for the Los
Angeles County mountains and Antelope Valley. And it is in effect
from this afternoon through midday Wednesday. Otherwise the Wind
Advisory for the Santa Barbara County South Coast and mountains will
remain in effect from this afternoon through early Wednesday
morning.
Guidance initialized a trough of low pressure with the axis centered
along 130w this morning reasonably well. The trough advanced
eastward and slightly amplified Monday through this morning. The
modified air mass within the trough had advanced along the central
coast and the vbg sounding had indicated a weaker capping marine
inversion than Monday morning. Little change to the marine layer had
occured over the bight as the thermal trough remained unchanged.
With modified air along the central coast and no change over the
bight...temperatures were 5 to 10 degrees cooler along the central
coast and 5 degrees warmer along the South Coast from yesterday at
this time. And the smx/sba pressure gradient differed from yesterday
by minus 1.4 at this time. Expect winds to reach advisory threshold
through all favored canyons along the entire Santa Ynez range this
evening and persist through Wednesday morning. 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 (sat-tue)...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...18/1800z.
Little change is expected in the weather pattern for the next couple
of days with some restriction to marine cloud coverage and a marine
layer depth of 1000 to 1500 feet. The marine cloud coverage will
stick primarily to the la and Ventura County coastal sections. Gusty
winds near ksba will cause low level wind shear...winds in the
mountains will cause turbulence and winds in the Antelope Valley
will cause blowing dust.
Klax...VFR conditions are expected through the evening with MVFR to
IFR conditions returning after midnight and continuing through much
of Wednesday morning. Good confidence in the 18z tafs.
Kbur...good confidence in VFR conditions through Wednesday morning.
&&
Lox watches/warnings/advisories...
red flag warning (see laxrfwlox).
Wind Advisory (see laxnpwlox).
Gale Warning (see laxmwwlox).
Small Craft Advisory (see laxmwwlox).
High rip current risk (see laxsrflox).
&&
$$
Public...30
aviation...Sweet
fire weather...gomberg
synopsis...kj
Www.Weather.Gov/losangeles
