Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Los Angeles/Oxnard California
210 PM PDT Tue Oct 25 2016
The weather will be dry and slightly warmer today and tomorrow
across the region. A cold front will bring locally gusty
southwesterly wind on Thursday and the possibility of moderate to
heavy rain late Thursday and early Friday. A cloudy and cool
Saturday will be followed by another chance of rain on Sunday.
Forecast concerns include potentially dense coastal fog tonight
and Wednesday morning, then a rather short-lived but potent storm
system Thursday night into Friday morning.
We had a tranquil day today across southwest California with
clear skies and generally light winds. A shallow marine inversion
will be in place for coastal stratus and potentially dense fog
overnight into the morning hours. A weak ridge builds tomorrow so
once the fog Burns off temperatures should warm a couple of
degrees over tuesday's highs. Mid and high-level moisture will
begin to brush the northern central coast area late Wednesday
afternoon in advance of an eastern Pacific storm system.
A low-latitude low pressure trough was taking shape over the
Pacific near 140w longitude and inline with computer models. On
Thursday afternoon this system will be about 250 nm west of Point
Conception with light rain reaching the central coast and moist
upslope on south-facing Santa Barbara foothills late in the day.
In other areas, clouds will be on the increase through the
afternoon but otherwise temperatures will remain rather mild.
A cold front will push across the region Thursday night then
exits Los Angeles County early Friday morning. The upper level low
pressure system lifts well north of our region during this time
frame, but the 90kt southerly jet slides across southwest
California overnight. Very deep precipitable water values are
expected with this system approaching 1.6 inches along the coast
which is near historical records for this time of year. Model data
suggests 3-hour rain amounts around 1 inch and there will be
MUCAPE values over 400 j/kg with strong forcing along the cold
front Thursday night. This leads US to believe there will be
period of moderate rain showers with embedded heavy downpours
associated with thunderstorms. The confidence factor for rain
rates over 0.5 inch per hour is growing and that could trigger our
first mud and debris flows of the season near recent burn scars.
Too early at this point to issue any watches, but this may be
needed as this event unfolds in the next day or so. The other
concern will be a strong low-level jet near the cold front which
indicates 50kt winds near ridge top level Thursday night. High-end
wind advisories may be needed for mountains and any thunderstorm
activity could generate damaging winds. Snow levels will remain
very high with this system, so no accumulations expected in our
mountains. Widespread rainfall totals of 0.5-1 inch are expected
across most areas with 0.25-0.5 inch in the desert, however,
foothills and mountains will likely see 1-2 inches, and the
favored coastal hills in San Luis Obispo County could see 2-4
inches before this one is done.
Friday will start out wet with the tail end of this storm system
shifting to our east, but we will mainly be dealing with
lingering scattered showers and clouds during the day. Cooler
temperatures are expected Friday due to wet ground and the air
A Gulf of Alaska low pressure trough reinforces southwest flow
aloft over California over the weekend. Another cold front will
remain north of our region Saturday, but some cloud cover is
likely across the central coast and overall temperatures do not
warm that much. This front slides across southwest California late
satuday night and Sunday with the focus for any rain staying
mostly north of Point Conception. For now have low chance
probabilities of rain for western sba and slo counties then. A
mixture of clouds will be found across the rest of the area with
another coolish day.
For early next week it looks like a weak ridge will build overhead
on Halloween for a dry day and moderating temperatures. There is
quite a bit of uncertainty in the medium range models beyond
Monday, but another weak trough could bring more rain to the
central coast to start the month of November on the right path.
At 1609z at klax...there was just a hint of a marine inversion
with marine layer depth of 700 feet.
Moderate confidence in the 18z tafs. VFR conditions will continue
through this evening followed by IFR conditions and marine clouds
affecting many of the coastal sections later tonight into
Klax...moderate confidence in the 18z taf. There is a 30 percent
chance of the marine clouds arrivig plus or minus two hours or
more in the onset of marine clouds.
Kbur...good confidence in the 18z taf. VFR conditions are
expected for the next 24 hours.
There is high confidence that winds and seas will remain below
Small Craft Advisory levels through at least Thu. South to southeast winds will
likely reach Small Craft Advisory levels by Thursday night for the outer waters as
the next Pacific storm moves into the region.