Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Los Angeles/Oxnard California
1100 PM PDT Sat Aug 27 2016
New aviation discussion
High pressure building aloft will bring a warming trend through
early next week, along with decreasing marine layer cloud
coverage. Triple digit heat is expected in some valley areas on
Monday and Tuesday. Cooler conditions and an increase in night
through morning low clouds and fog are expected for the second
half of next week as a broad trough of low pressure develops.
Upper level low pressure system to the east near the Colorado
River valley helped to maintain a fairly deep marine layer
pattern and mild temperatures today. As the low pressure system
continues to move eastward, an upper level ridge of high pressure
will begin to build over southwest California during the next few
days. The marine layer depth is expected to range between 1500
and 2000 feet tonight, with low clouds and fog still expected
to reach some of the valleys by sunrise. The marine layer depth
is expected to shrink through the day on Sunday.
Other short term concern is localized sundowner winds occurring
this evening across the foothills from Gaviota to San Marcos Pass.
The current Santa Barbara-Santa Maria gradient is only -2.7 mb
but we are seeing gusts up to 44 mph at Refugio and up to 32 mph
at San Marcos Pass. Will be updating forecast to increase winds
for these areas tonight. The sundowner winds are expected to
become slightly more widespread Sunday night through Tuesday
night, as the Santa Barbara-Santa Maria gradient is expected to
increase to around -4 mb each evening. Wind advisories may need to
be issued for these upcoming evenings, but the focus of the
strongest winds will remain across western portions from Gaviota
to Goleta. There will be elevated fire danger across the sba South
Coast and all interior sections Sunday through Tuesday...please
see fire discussion below for details.
Significant warming trend still on track for tomorrow, with most
inland areas climbing well into the 90s. Temperatures then
expected to peak on Monday, when several locations in the
valleys, lower mountains, and deserts are expected to climb
above 100 degrees.
*** From previous discussion ***
An upper level trof over sern California this afternoon will move E thru
tonight. At the same time, an upper level ridge will build along
the central California coast. The ridge will build further into swrn California
thru sun, then persist over the area with 500 mb heights around
591 dm thru Mon. The upper ridge will weaken some Mon night and
Tue as an upper level trof moves into northern California.
The marine layer pattern with night and morning low clouds and fog
for coastal areas is forecast to continue tonight thru Tue. However,
the marine inversion should lower enough tonight to prevent the low
clouds from moving well inland over vtu/l.A. Counties. The inversion
should then lower further to below 1000 ft Sun night and continue
thru Tue morning with low clouds confined to the coastal plain,
except the sba County S CST should remain clear due to northerly
canyon winds. In addition, patchy dense fog can be expected with the
low clouds Sun night and Mon morning, and again Mon night into Tue
morning. Some mid level moisture should move in during the period as
well, with a few afternoon cu buildups possible in the mtns.
Otherwise, mostly clear skies will continue across the region thru
Tue. Weaker onshore gradients will persist during the afternoon and
evening hours, with local gusty S to W winds at times in the
foothills, mtns and deserts. Some generally weak offshore flow is
expected night and morning hours Sun night thru Tue morning, with
gusty sundowner winds expected along the sba S CST and mtns.
Temps are forecast to have a warming trend with highs several
degrees above normal away from the coast on sun, and 4 to 10 deg
above normal for many areas Mon and Tue. The warmest vlys and
foothills on Mon and Tue will reach the upper 90s to 103.
There is generally good agreement between the GFS and ec in the
medium range. A broad upper level trof can be expected along and off
the California coast Wed thru Sat, with a dry SW flow aloft over swrn California.
The upper trof will promote a bit stronger onshore flow, cooler
temperatures and a deeper marine inversion by late next week.
The marine layer pattern will become more organized during the
period, with widespread night and morning low clouds and fog
expected for the CST and vlys including the Santa Clarita Vly by the
end of next week. Otherwise, mostly clear skies will prevail across
the region. Breezy afternoon and evening S to W winds will prevail
thru the period, especially over the foothills, mtns and deserts.
Temps will have a cooling trend later next week, with highs falling
to 5 to 10 deg below normal by Sat. The warmest vlys and foothills
should reach the upper 80s to mid 90s on Wed, then be only in the
80s by Sat.
At 0520z the marine layer at lax was 1000 feet deep with an
inversion top of 3800 feet with a temp of 24 degrees c.
Low confidence in cstl tafs. IFR cigs could develop anytime after
08z but will likely hold off until near dawn. There is a 30 percent
chc of no cigs at each coastal Airport. Low confidence in clearing
times if clouds do arrive and fcst could be off by as much as 90
Moderate confidence in Vly tafs with only a 30 percent chc of LIFR
cigs from 12z-16z.
Very good confidence in inland tafs.
Klax...low confidence in taf with equal chc of cig arrival any time
between 09z and 13z. There is a 30 percent chc of no cigs at all. If
cigs do arrive...clearing will occur within 90 minutes of fcst.
Kbur...moderate confidence in taf with a 30 percent chc of LIFR cigs
Low-end Small Craft Advisory conditions under northwest winds
will persist into early Sunday morning across the outer waters
from Point Sal to San Nicolas Island. Stronger small craft
conditions are likely by late Sunday afternoon and overnight into
early Monday, possibly extending northward to cover all outer
waters from Piedras Blancas to San Nicolas Island. Portions of
the near-shore waters may see Small Craft Advisory winds and seas as well Sunday
afternoon & evening.
Gale force gusts will be possible Monday and Tuesday
evening/night across the outer waters. Small craft conditions may
extend into the inner coastal waters at times especially from
Point Piedras Blancas to Point Sal and the western portion of the
Santa Barbara Channel.
Small craft conditions due to continuing gusty northwest winds
and steep seas may continue at times across the outer coastal
waters through late next week.
Elevated fire danger Sunday through Tuesday for interior sections
of southwest California for the mountains, interior valleys, and
deserts, there will be significant warming on Sunday, with the
peak of the heat occurring Monday into Tuesday when many areas
will reach triple digit temperatures. Minimum humidities will
generally range between 10 and 20 percent during this time, with
isolated single digit readings possible in the mountains and
Antelope Valley on Monday and Tuesday. The warming temperatures
will cause steepening lapse rates that will enable deep vertical
mixing layers, especially on Monday and Tuesday when mixing layer
heights could range between 12,000 and 15,000 feet. For existing
fires or new ignitions over interior areas, plume dominated fire
behavior will be possible.
The other area of elevated fire danger will be the sba South
Coast and Santa Ynez Mountains where gusty sundowner winds are
expected each night from Sunday through Tuesday. The sba-smx
gradient is expected to peak around -4 mb each night, which will
favor the strongest winds across western portions of the South
Coast and Santa Ynez Mountains (mainly from Gaviota to goleta).
These areas could see wind gusts of 30 to 40 mph. Each night,
there is also the potential for some localized north to northeast
wind gusts that could impact the eastern portions of the sba
County mountains and foothills (including the upper elevations of
the rey fire) and the Montecito hill area...with the highest
probability being late Monday night into Tuesday morning when the
Santa Barbara- Bakersfield gradient peaks at -3.5 mb. The gusty
sundowner winds will also bring warming and drying to the
foothills and wind exposed locations. Peak warming and drying is
expected Monday evening when temperatures could rise into the 90s
and humidities could fall to between 15 and 25 percent.
Pz...Small Craft Advisory in effect until 3 am PDT Sunday for
zones 673-676. (See laxmwwlox).