Scientific Forecaster Discussion
fxus66 klox 201613
Area forecast discussion
National Weather Service Los Angeles/Oxnard California
913 am PDT Mon Aug 20 2018
This week, the high system will move east for above normal
temperatures and fair skies, except for an overnight coastal
marine layer that may spread into some valleys, at times. Next
week, a low system may approach for increasing clouds.
Short term (tdy-wed)...20/912 am.
An eddy has spun up this morning pushing the marine layer depth
over 2500' south of pt Conception based on the latest lax
profiler data. This should result in some cooling at least for
inland areas and especially the Lower Mountain slopes below 3000'
where temps are already running almost 10 degrees cooler than
yesterday at this time. Valley forecast temps may be a few
degrees on the high side today with the low clouds lingering
longer than yesterday but otherwise the forecast looks good. Will
probably see similar low cloud coverage Tuesday morning and
generally little change in the other parts of the forecast as
***From previous discussion***
Dry SW flow aloft will set up between these two systems over
Hgts fall form 592dm today to 590dm Tue and Wed. Max temps will
dip a degree or two Tuesday as the hgts fall. Wednesday will not
see much change at all.
Max temps will be pretty close to normal while overnight lows will
remain 3 to 6 degrees above normal.
The weak onshore push will bring low clouds to most of the coasts
each night through morning and since the marine layer 1100 ft deep
there will be local stratus incursions into the lower vlys right
around or even a little after dawn.
The only winds of note will be across the western portion of the
Antelope Vly and even there the west winds will be well under
Long term (thu-sun)...20/320 am.
Weak ridging will build back into the state from the southeast Thursday
and this will persist through the weekend. The upper level flow
will remain from the SW so there is no threat of monsoon
transport. Hgts really do not change much and temperatures will
really not change much from day to day either. Weak onshore flow
will keep the night through morning coastal stratus pattern going
although weak sundowners may keep the sba South Coast cloud free.
A slightly stronger sundowner might occur Friday and Saturday
nights but it does not look that strong.
At 1100z at klax, the marine layer was around 1700 feet deep. The
top of the inversion was near 3600 feet with a temperature of 27
North of Point Conception...high confidence with LIFR/IFR cigs for
coastal tafs this morning through 15z. Then moderate confidence
with timing of stratus to scour out within +/- 1 hour from 12z
tafs. High confidence with VFR conds at kprb. 20% chance for IFR
between 14-16z. Moderate confidence with similar timing and
conditions this evening into Tue morning.
S of Point Conception...moderate confidence tafs with IFR/MVFR
cigs. Lower confidence with timing kbur and kvny IFR/low MVFR
cigs. 30% chance that cigs could scour out +/- 2 hours for coastal
areas. Low to moderate confidence with similar timing and
conditions this tonight into Tue morning. 50% chance that cigs
will not develop in coastal valleys.
Good confidence in desert tafs.
Klax...moderate confidence in taf. There is a 20 percent chc of
IFR cigs 12z-14z. Good confidence that any east wind component
will be under 5 kt. VFR transition should occur within one hour
Kbur...low confidence in IFR to low MVFR taf from 13z-16z with a
40 percent chc of no cigs...otherwise high confidence.
For the outer waters, overall it will remain fairly quiet with northwest
winds between 10 to 20 kt strongest in the afternoon and evening
hours. Strongest western portions. There will be a 20-30% chance
for Small Craft Advisory level gusts each late afternoon and evening for areas
between Point Conception to northwest of San Nicolas Island. The next
decent chance 50% for small craft advisories (sca) should not be
until Wednesday evening between Point Conception to northwest of San
Nicolas Island. Higher chance for widespread Small Craft Advisory level winds
beginning Thursday afternoon and continuing through late this
For the inner waters, conditions are expected to remain below
Small Craft Advisory levels through Thursday.
Patchy fog, possibly dense at times will continue to form during
the late night and morning hours, especially north of Point
Conception through at least Wednesday.
Hazard potential outlook (wed-sun).
Gusty sundowner winds and elevated fire weather conditions are
possible for late this week.