Southwest California area forecast discussion
National Weather Service Los Angeles/Oxnard California
830 PM PDT Tuesday may 21 2013
Synopsis...
Gusty west to northwest winds will occur in the mountains...deserts...and
portions of the coast into Thursday. An area of low pressure will persist
across the region...and will gain strength over the weekend to deepen the
marine layer and bring drizzle. The afternoon temperatures will stay below
normal through next Tuesday...then a warming trend starts with temperatures
reaching above normal by midweek.
&&
Short term (tonight-fri)...strengthening onshore flow brought a cooling
trend to most areas today...with the exception of the mountains and
Antelope Valley. Lax-Daggett gradient peaked at around +7 mb which helped
to generate gusty onshore winds in the mountains and Antelope Valley.
The strongest winds this evening have been focused across the foothills
of the Antelope Valley...with Lake Palmdale observing a gust of 47 miles per hour
this past hour. Meanwhile...widespread gale force winds are impacting
the outer coastal waters this evening. The tightening northwest gradient
is also reflected across sba County...where the current sba-smx gradient
is -4.2 mb. As a result...locally gusty sundowner winds are impacting the
western portions of the sba County South Coast this evening...with local
gusts over 35 miles per hour.
As the upper trough deepens across the region on Wednesday and
Thursday...the cooling trend will continue and push further inland.
Gusty onshore winds will continue across the mountains and Antelope
Valley...approaching advisory levels each afternoon and evening. As
the northwest gradient tightens on Wednesday across the coastal
waters and sba County...the gale force winds will become more widespread
extending into western portions of the sba channel. Also...winds
are expected to exceed advisory levels across the central coast and
sba South Coast/mountains on Wednesday afternoon and evening. In
fact...sba-smx gradient is expected to jump to around -5.5 mb on
Wednesday evening. This in combination with good thermal advection
and some upper level wind support will likely generate wind gusts up
to 50 miles per hour across favored passes and canyons of southern sba County.
While this is not a particularly warm sundowner event...could still
see some favored downslope locations exceed 80 degrees on Wednesday.
Please see fire discussion below for more details on elevated fire danger.
*** From previous discussion ***
If the models are to be believed, the trough briefly lifts on Friday,
resulting in a very slight warming trend Friday, maybe a few degrees
at most, and earlier marine layer clearing.
Long term (sat-tue)...trough deepens again over the Holiday weekend.
Decreasing northwest flow should allow the low clouds to spread up
the coast through slo County and we may see areas of drizzle again
each morning through Monday. Limited coastal clearing and clouds may
linger into early afternoon for some of the valleys. Daytime temperatures
expected to run 2-4 degrees below normal. The trough is expected to
shift east Tuesday for a warming trend going into the middle of next
week.
&&
Fire weather...
as winds ramp up Wednesday afternoon and evening across the sba
South Coast and mountains...I-5 corridor of the la/vtu County mountains...
and Antelope Valley...there will be elevated fire danger across all
of these areas. Humditiy levels could briefly fall below 15 percent
across the sba South Coast on Wednesday afternoon. Similar low humidities
will likely impact the I-5 corridor and Antelope Valley during the
late afternoon and evening hours. As a result...all of these areas could
experience brief critical fire weather conditions...especially considering
the very dry fuels for this time of year. However...it does not appear
that durations of critical fire weather conditions will be met to issue
red flag warnings for this event.
&&
Aviation...21/2355z.
Satellite imagery showing low clouds surging quickly into the la
County coastal areas late this afternoon...including klax. Clearing
being observed to the northwest of la County. Lower confidence in
low clouds returning to coastal areas north of Point Conception...with
higher probability of ceilings across la County coast/valleys tonight.
Appears that eddy will be strong enough to bring low clouds back
into koxr early Wednesday morning. Eddy circulation expected to maintain
ceilings in MVFR category for the most part...with the exception of a 30 percent
chance of IFR conditions in the valleys (including kbur and kvny).
Gusty winds across the passes and canyons of sba County this evening
and somewhat stronger tomorrow evening...bringing a good chance of low level wind shear
both evenings. Also...gusty west to northwest winds will be affecting
ksmx...ksbp...kpmd...and kwjf through period.
Klax...low clouds surging in quickly as of 00z with MVFR ceilings already
observed. Current thinking is that low clouds will likely linger for
the night...but there is a 30 percent chance that low clouds could scour
out for a few hours later this evening before returning. Ceilings generally
expected to remain in MVFR category.
Kbur...fairly high confidence that low clouds will return overnight into
Wednesday morning. Leaning towards MVFR category...but a 30 percent chance
of IFR conditions.
&&
Lox watches/warnings/advisories...
Gale Warning (see laxmwwlox).
Small Craft Advisory (see laxmwwlox).
High rip current risk (see laxsrflox).
&&
$$
Public...gomberg/mw
aviation...gomberg
fire...gomberg
synopsis...kj
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