Scientific Forecaster Discussion
fxus66 klox 151925
Area forecast discussion
National Weather Service Los Angeles/Oxnard California
1225 PM PDT sun Sep 15 2019
Temperatures will be cooler across the region today and much
cooler through Friday then gradual warming begins next weekend.
Overnight and morning low clouds and fog will return to most
coastal and adjacent valley areas this week.
Short term (tdy-tue)...15/924 am.
Temperatures across the region are notably cooler this morning.
Dips of three to seven degrees are common in most inland locations
with larger drops along the coast and many locations along the
central coast with drops of fifteen or greater degrees as compared
to this time yesterday. A few mountain locations are up to a few
degrees warmer as are sites in the Antelope Valley due primarily
to compressional heating. But overall the cooling trend has begun
and lower temperatures will remain through the week.
No notable changes to the current forecast package are
anticipated as the timing of the incoming troughs appear to remain
on track with expectations. Will be looking at winds in relation
to the course and strength of the first trough particularly gusty
sundowner winds late Monday - as well as how strongly the onshore
flow develops and this may lead to adding a bit more marine cloud
coverage. All of which will result in tweaking temperatures a
At this time no precipitation will be added to the forecast as
moisture is limited at peak instability. Something to keep an eye
on but there should be little impact unless it becomes more
***From previous discussion***
The marine layer is 700 ft deep. Gradients are weakly onshore both
to the north and the east and both are trending more onshore.
Saturday's ridge has been replaced SW flow at the base of a West
Coast trof. There are patches of stratus affecting the la coast
and the central coast (by dawn some stratus will likely develop
over the vta coast). There is also a large amount of mid and high
level clouds riding into the area in the SW flow. Today will be
partly to mostly cloudy day. The clouds, onshore flow and trends
and lowering hgts will all combine to bring about a nice cooling
trend. Max temps will be down 4 to 8 degrees across la and vta
counties while slo and sba counties will see at least 8 degrees of
cooling but the central coast will drop 14 to 18 degrees.
There should be a slightly better developed marine layer cloud
pattern Monday morning as the lower hgts, increased onshore flow
and cyclonic turning should enhance low cloud formation. The
marine layer is not forecast to deepen too much so most of the
vlys should remain clear. The mid and high level clouds will be
east of the area and aside from the low clouds skies should be
mostly sunny. In the afternoon or early evening however a little
patch of instability/positive vorticity advection is forecast to roll through with the trof
and it might produce a little elevated convection, maybe some
virga and even a little shower across the tallest mtn peaks. It
looks like it will be moisture starved however and unless it finds
some moisture it will likely just produce a few mid level clouds.
The coasts will cool a few more degrees but there will be another
5 to 10 degrees of cooling across the interior and Max temps will
mostly end up about 5 degrees blo normal.
Advisory level sundowner winds will likely develop across southern
sba County in the wake of the trof Monday night.
Dry northwest flow sets up over the state on Tuesday. The mixing from the
trof and the northerly push behind the trof will limit the marine
layer clouds from forming in any great way. Offshore trends will
help the vlys and csts warm a few degrees but since hgts remain
about the same the interior will not see much change in temps.
Long term (wed-sat)...15/302 am.
Both the ec and the GFS agree that a cool upper low will move out
of waters to the west of British Columbia...open up into a trof and move into
California Wednesday and Thursday. Right now it looks like it will deepen the marine
layer and bring a little cooling Wed and then 4 to 8 degrees of
cooling Thu. Right now all indicators are showing that this will
be dry system but there is a small but non zero chc of this
producing a shower or two late Thursday morning or afternoon. More
likely is some morning drizzle. There will likely be a pretty
strong sundowner Thursday night behind the trof axis.
Ec and GFS continue in good agreement through Saturday. Broad West
Coast troffing is forecast Friday and it should be fairly routine
day albeit one with blo normal temps.
Weak ridging and offshore trends move in on Saturday and it will
make for a very pleasant day with sunny skies and an 4 to 8
degree jump in temps leading to near normal Max temps.
At 1708z, the marine layer depth was around 900 feet deep at
klax. The top of the marine inversion was near 2800 feet with a
temperature of 25 degrees celsius.
Moderate confidence in the 18z tafs. Currently, conditions are VFR
across the district. The marine clouds are hugging the coast,
however, and ready to pounce on coastal sections earlier this
evening. The marine layer will deepen tonight, almost eliminating
the threat of dense fog. Expect IFR to LIFR conditions tonight in
coastal sections with some improvement to MVFR conditions Monday
morning. Most valley tafs will see some changes by Monday, with kbur
and kvny getting brief MVFR visibilities and kprb will probably
get MVFR ceilings late tonight. The Antelope Valley taf sites will
have a return of gusty afternoon and evening winds starting this
Klax...there is a 30 percent chance of ceilings arriving plus or
minus three hours from the forecasted time.
Kbur...VFR conditions are expected through the period, except for
MVFR visibility early Monday morning. There is a 30 percent chance
of IFR ceilings early Monday.
Moderate confidence in the current forecast. Higher confidence in
winds, less confidence in swells. Small Craft Advisory (sca) level
winds will likely develop through Monday evening over most of the
coastal waters. There is a 50 percent chance of Small Craft Advisory level winds
across the near shore waters north of Point Sal and 30 percent
chance across the inner waters south of Point Mugu. Periods of
steep seas will develop at times, especially across the northern
and inner waters.
Winds will likely diminish some between Tuesday and Tuesday
night, then winds will likely develop across the entire coastal
waters between Wednesday and Thursday.
A southerly swell developing with Hurricane Kiko will move over
the coastal waters between late Monday night and Wednesday. There
is a 40 percent chance that elevated surf of 3 to 5 feet could
break near shore and in the vicinity of jetties at times during
Patchy dense fog is possible across portions of the coastal
waters this morning. Visibility may be reduced to one nautical
mile or less at times through late this morning.
Hurricane Kiko has strengthened to a major hurricane today.
Strong rip currents are possible at area beaches between Tuesday
and Wednesday. A high rip current risk is likely for this period.
There is a 50 percent chance that elevated surf between 3 and 5
feet is possible on Tuesday and Tuesday night. Before entering the
water, ask a local lifeguard about hazardous areas and the latest
Fire weather...15/914 am.
An upper level trough of low pressure will bring strengthening onshore
flow to the region today through Monday. Onshore winds are expected to
gust between 25 and 40 mph across interior sections today, then
increase to 30 to 45 mph by Monday. Temperatures across inland areas are
still expected to be in the 90s today, with further cooling on Monday.
Meanwhile, humidities between 8 and 15 percent will be common across
interior sections today. By Monday, a stronger onshore flow pattern
combined with a deepening marine layer will bring cooling and humidity
recovery to coastal and valley areas, however a pocket of drier air will
remain in the la/Ventura County mountains and Antelope Valley where
there could still be humidities between 10 and 20 percent. The gusty
onshore winds combined with lingering dry air will bring elevated to
brief critical fire weather conditions to all interior areas today,
then mostly confined to the la/Ventura County mountains and
Antelope Valley by Monday. There will be gusty northwest winds
Monday night across western portions of the Santa Barbara South Coast
and adjacent foothills, but humidity levels are expected to remain
Pz...Small Craft Advisory in effect until 3 am PDT Monday for zone
670. (See laxmwwlox).
Small Craft Advisory in effect until 3 am PDT Wednesday for
zone 673. (See laxmwwlox).
Hazard potential outlook (tue-sat).
No significant hazards expected.