Scientific Forecaster Discussion
fxus66 klox 240440
Area forecast discussion...updated
National Weather Service Los Angeles/Oxnard California
940 PM PDT Wed may 23 2018
Onshore flow will continue night through morning low clouds and
fog into next week. A low pressure system over the eastern Pacific
Ocean will bring patchy overnight drizzle through Friday. The low
pressure system should exit by next week to raise temperatures to
Short term (tnt-sat)...23/937 PM.
The latest satellite imagery indicates weak ridging aloft over
Southern California this evening, while a trough of low pressure
near 34n and 133w slowly moves toward the West Coast. Weak
ridging aloft inhibited the clearing of the marine layer stratus
earlier today as the marine inversion tightened some. More "may
gray" like weather looks to be the staple of the weather pattern
through the end of the week.
The upper-level trough, located about 700 miles west of Point
Conception will increase onshore pressure gradients over the next
couple of days. A muddled cloud pattern is evident on fog product
imagery this evening should fill in overnight and into Thursday.
Low clouds and fog will struggle to clear again on Thursday
afternoon, especially across the Los Angeles basin, as strong
onshore flow develops across the area.
Developing south to southwest flow aloft ahead of the trough
tonight will push a weak vort Max toward the area on Thursday
morning. With the deep marine layer already in place, some concern
exists that patchy drizzle could develop mainly south of Point
Conception. A better drizzle scenario looks to play out Friday
and Saturday, possibly turning to light showers between Friday
night and Saturday. An update will be issued to increase pops the
next several nights and add patchy drizzle for Thursday morning.
*** From previous discussion ***
The inversion will either remain the same or deepen with the next
low approaching so expecting similar gloomy conditions Thu-Sat
with some drizzle at times, mainly south of pt Conception and
especially upslope areas of eastern of la County. The exceptions
being the far interior and mountains above 5000'. Also, gusty
sundowner winds are expected to develop by Friday afternoon across
srn sb County and continue through Saturday, possibly reaching
advisory levels at times, so low clouds will likely be cleared out
from there. Otherwise, lots of clouds, drizzle at times, below
normal temps, and gusty winds in the av and srn sb County.
Long term (sun-wed)...23/131 PM.
The upper low is expected to slowly move east by Sunday, resulting
in at least weak ridging and warming aloft that will lower the
marine layer depth through early next week. At the same time
onshore flow will be weakening so most areas should see a
noticeable warming trend, though most significant inland with
valley highs back up into the 80s. There will still be a solid
marine layer for coast and most valleys but it will clear much
earlier for the valleys while possibly lingering near the coast
into the afternoon. Sundowner winds expected to diminish Sunday
with no significant wind issues through the middle of next week.
At 00z, the marine layer depth was around 3300 feet deep at klax.
The top of the inversion was around 4800 feet with a temperature
near 16 degrees celsius. The marine layer is expected to deepen
between 4000 and 4500 feet asl.
Moderate-to-high confidence in the current forecast. Highest
confidence in MVFR conditions at coastal and valley terminals
developing through 09z. Lower confidence in clearing on Thursday.
There is a chance of IFR conditions at coastal and valley
terminals between 09z and 16z. MVFR conditions to VFR conditions
with ceilings at or below 5000 feet will likely linger across most
terminals on Thursday.
Klax...MVFR conditions will spread back into klax between 03z and
07z. There is a 30 percent chance of IFR conditions between 10z
and 16z. Klax will likely struggle to clear on Thursday. Highest
confidence in VFR conditions with scattered clouds after 22z or
23z, but there is a 20 percent chance of MVFR conditions
lingering throughout the afternoon and evening Thursday, with an
equal chance of ceilings at or below 5000 feet lingering.
Kbur...MVFR conditions will spread into kbur between 06z and 11z.
There is a 40 percent chance of IFR conditions between 11z and
15z. With strong onshore pressure gradients, MVFR conditions to
VFR conditions with ceiling at or below 5000 feet will likely
linger throughout the afternoon and evening Thursday.
For the outer waters, high confidence in the current forecast.
Winds and seas will remain below Small Craft Advisory levels
through at least Friday. There is a 60 percent chance of Small
Craft Advisory level northwest winds across the southern portion
of the outer waters from Point Conception to San Nicolas Island
from Friday night through Sunday. Confidence is somewhat lower
for advisory level gusts for the northern portion of the outer
waters from Saturday afternoon through Sunday.
For the inner waters, generally high confidence in the current
forecast. For the waters north of Point Sal, winds and seas will
remain below Small Craft Advisory levels through Monday, except for a 40 percent
chance of Small Craft Advisory level winds Saturday night.
For the waters south of Point Conception, winds and seas will
remain below Small Craft Advisory levels through Friday. For Friday night through
Sunday, there is a 60 percent chance of Small Craft Advisory level winds at times,
especially across western sections of pzz650.
A long period southerly swell will continue to move through the
coastal waters through Thursday. Locally rough conditions may
occur at local Harbor entrances, especially those with southerly
California...beach hazards statement in effect through Thursday evening
for zones 40-41-87. (See laxcfwlox).
Hazard potential outlook (sat-wed).
Advisory level sundowner winds are possible for western portions
of the sb South Coast this weekend.