Scientific Forecaster Discussion
fxus66 klox 280236
Area forecast discussion
National Weather Service Los Angeles/Oxnard California
736 PM PDT Sat may 27 2017
an upper level ridge of high pressure and a lowering marine layer
will support a warming trend through early next week. The high will
be replaced by a weak upper level trough of low pressure by the
middle of next week providing a cooling trend with more widespread
night and morning low clouds for the coast and valleys.
Latest satellite imagery was indicating mostly clear skies across
the forecast area, with the exception of some stratus pushing
along the Santa Barbara central coast. Some higher level clouds
were sweeping across the sba South Coast into Ventura County. High
clouds should only last for a few hours this evening. Latest
acars sounding near lax was showing the marine layer depth around
1500-1700 ft early this evening. Onshore gradients were around 2mb
weaker compared to yesterday at this time. With a weak eddy
expected to develop late this evening, low clouds should be slow
to develop across la County coastal areas, while the central coast
should see widespread low clouds after midnight. Would like to
see better organized stratus across the coastal waters, but with
somewhat of an eddy, low clouds should affect la coastal areas and
possibly into Ventura coastal areas before dawn Sunday morning.
As for today, high temperatures were able to rebound nicely due to
weak offshore flow across interior areas and with high pressure
building aloft. Portions of the Antelope Valley warmed nearly 20
degrees today as well as a few Lower Mountain locations. Highs
reached the upper 80s to around 90 across the Antelope Valley,
which is a few degrees warmer than normal for this time of year.
La to sba County valleys ranged 3-9 degrees warmer compared to
yesterday, with San Luis Obispo interior valleys warming up over
10 degrees. Paso Robles was 14 degrees warmer at 83 degrees.
Coastal areas near the beach were about the same as yesterday, or
a degree cooler today. The only changes made to the forecast this
evening was taking out low clouds for the San Fernando Valley as
newest high res models keep low clouds limited to coastal areas as
well as the San Gabriel valley. Otherwise, no other changes were
made to the forecast this evening. Confidence is not terribly high
that this will happen as the marine layer should end up around
1000- 1400 ft deep. There could be some low clouds filtering in
the southeast portion of the sfv, but should not be widespread if it
***From previous discussion***
The marine layer is expected to shrink to around 1500 feet later
tonight into Sunday, as a weak offshore flow component develops
over the interior sections of the forecast area. This will result
in a further reduction of low cloud coverage for Sunday morning,
and lead to additional warming across the region. In fact, valley
areas are expected to climb well into the 80s on Sunday while the
Antelope Valley soars into the lower to mid 90s. Similar warm
temperatures expected on Monday. A weak upper level trough will
move into the area on Tuesday bringing an influx of higher level
clouds and a few degrees of cooling.
The GFS and European model (ecmwf) models in fairly good agreement on deepening
upper level trough for Wednesday across forecast area. This system
will likely bring a deepening of the marine layer while model
cross sections showing increased mid and high level clouds. Have
introduced a slight chance of showers for Wednesday afternoon
across north facing slopes and Antelope Valley. All portions of
the forecast area should see noticeable cooling on Wednesday. Weak
upper level ridge of high pressure will bring a slow warming
trend Thursday into Friday with little change into Saturday.
At 2330z, the marine inversion at klax was based at 1700 feet.
The top of the inversion was 5000 feet with a temperature of 17
High confidence for VFR everywhere through 06z...except for an
occasional MVFR ceiling at ksba through 02z. Marine layer and ceiling
should lower tonight into Sunday. For coastal areas north of Point
Conception, IFR or brief LIFR cigs should develop between 6-9z.
40% chance that LIFR/IFR cig will develop at kprb after 10z. Scour
out times should occur within +/- 1 hour from 00z taf.
S of Point Conception, moderate to high confidence that IFR to low
MVFR cigs will develop across la/vtu coastal sites after 08z and
around 11z for koxr. 30% chance that cigs will not develop at koxr
or kcma. 30% chance for cigs to develop at ksba after 12z after
this brief cloud deck moves through this early evening.
Klax...moderate confidence with 00z taf. Lower confidence with
timing but better confidence for low MVFR cigs. 30% that cigs
could start out as IFR for a couple hours. Ceilings should return
sometime between 07z and 10z.
Kbur...high confidence in 00z taf through 10z, 40% chance that
LIFR/IFR cigs could develop after 12z through 16z.
80 percent chance of low-end Small Craft Advisory (sca)
conditions from the central coast to San Nicolas Island (outer
waters) late this afternoon...becoming certain by Sunday...after
which Small Craft Advisory conditions should persist at least through Wednesday.
Some of the winds will spill into the western half of the Santa
Barbara Channel each evening, but at this point does not look
expansive enough to warrant a Small Craft Advisory for the whole channel. These
winds will create a short period chop over all waters including
the Santa Barbara Channel and Santa Monica basin (inner waters).
The winds peak Monday and Tuesday and there is a chance that gale
conditions form beyon 30 nm of the central coast.
Pz...Small Craft Advisory in effect from 3 PM to 9 PM PDT Sunday
for zone 645. (See laxmwwlox).
Small Craft Advisory in effect until 6 am PDT Monday for
zones 670-673-676. (See laxmwwlox).
Hazard potential outlook...(tue-sat)
no significant hazards expected.