Area Forecast Discussion
Issued by NWS Los Angeles, CA
FXUS66 KLOX 290325
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
825 PM PDT WED SEP 28 2016
Weak high pressure will bring fair skies and warm temperatures to
the area on Thursday. A broad upper level trough of low pressure will
arrive on Friday to cool temperatures to below normal and increase
the marine layer into early next week.
Scattered thunderstorms persisted over the VTU County mtns thru
about 7 PM. There were a few showers lingering over the VTU County
mtns and parts of the VTU County interior vlys this evening. This
shower activity is expected to dissipate by mid evening. There were
plenty of mid level clouds over portions of VTU/L.A. Counties as
well which should thin out a bit overnight. Low clouds were noted
along the Central Coast and should move inland some over the coastal
plain overnight along with patchy dense fog. Otherwise, clear to
partly cloudy skies can be expected across the forecast area
An upper level low over sern CA this evening will weaken and give
way to weak upper ridging later tonight and Thu. A broad upper level
trough will start to move into swrn CA from off the ern PAC by Fri,
then push into the region thru Sat.
There will be some lingering mid level clouds mainly over VTU/L.A.
Counties on Thu, with the low clouds along the Central Coast
clearing off the coast by afternoon. Some building cu will also be
possible over the VTU/L.A. County mtns in the afternoon, but no
shower or thunderstorm activity is expected. The marine inversion
will gradually deepen Fri thru Sat, with night and morning low
clouds and fog expected to persist along the central Coast and
spread into the Santa Ynez Vly. S of Point Conception, the marine
layer clouds will be slow to reorganize, but by Fri night into Sat
morning, low clouds and fog are expected to become a bit more
widespread over the coastal waters and push into mainly the L.A.
County coast as an eddy develops. Otherwise, mostly clear skies can
be expected across the forecast area thru Sat.
Onshore flow is expected to gradually increase thru Fri, then
gradients will turn more northerly thru Sat. For Fri evening, gusty
northerly canyon winds at least close to advisory levels at times
can be expected across the SBA County s coast and mtns, with
offshore flow over SLO/SBA Counties thru Sat morning.
Temps are forecast to remain a few degrees above normal across the
region Thu and Fri, then cool to near normal to slightly below
normal for Sat. Highs in the warmest vlys and foothills Thu will be
in the upper 80s to lower 90s, then cool to the upper 70s to low 80s
***FROM PREVIOUS DISCUSSION***
The trough that moves through Friday night into Saturday will be
the first of several that will mostly impact northern California.
There are a couple of weak cold fronts that will mostly wash out
before reaching SLO county, the first one late Sunday and then
another late Monday. Models aren`t fully in agreement but none of
them show any of these troughs holding together well enough to
generate any rain, even for the Central Coast. So will maintain a
dry forecast for now. Main impacts initially will be the cooler
temps and persistent northwest flow that will continue to generate
advisory level winds at times in the usual areas. As we get into
the middle and end of the week high pressure aloft will build into
California from the west while a surface high builds over the
Great Basin. While the air mass warm up gradients will be shifting
to offshore and we may be looking at another Santa Ana event by
At 2310Z...the marine inversion at KLAX was near surface-based.
The top of the inversion was at 1300 ft with a temp of 26 deg C.
Generally hi confidence in the 00Z TAFs. There is a 60-70 percent
chance of low clouds and LIFR conditions at KSBP and KSMX from about
08Z-18Z tonight and Thu morning, altho the timing of the onset of
the low clouds may be off +/- an hour or so. Otherwise, VFR
conditions can be expected at all airfields thru Thu afternoon.
KLAX...Hi confidence in the 00Z TAF with VFR conditions expected
thru Thu evening.
KBUR...Hi confidence in the 00Z TAF with VFR conditions expected
thru Thu afternoon.
Mostly light winds are expected across the coastal waters through
Thu with SCA conds not expected. Northwest winds are expected to
increase across the outer waters and northern inner waters
late Thu through Fri, with SCA conditions likely in those areas
Fri evening through at least Sun. There is a 50 percent chance
that SCA conds will spread into the SBA Channel and the southern
inner waters by Sat afternoon continuing through Sun.
There is a 20 percent chance of Gale Warning conditions sometime
this weekend mainly across the outer waters from Point Conception
to San Nicolas Island.
Extra surging and currents are possible near the coast due to a
long period south swell of 2 to possibly 4 feet by Thursday
morning, peaking late in the day into Friday before subsiding this
Locally dense fog is possible across much of the coastal waters
tonight through Thursday morning.