Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Los Angeles/Oxnard California
1055 am PDT Thu Oct 27 2016
..updated aviation discussion...
A storm system will spread rain across the area from north to
south today through Friday. Heavy rain and thunderstorms are
possible tonight through Friday morning. A couple of weaker
systems could bring light rain to some areas again on Sunday and
Tuesday. Temperatures will remain near or below normal through the
middle of next week.
A very moisture laden system is just off the coast this morning.
The upper low itself is still about 600 miles southwest but it's
tapping into an air mass whose precipitable water is close to 2".
The last few model runs have focused the bulk of this moisture on
the central coast tonight before weakening considerably as it
moves east across the area. There will likely be a very large
orographic bias to the rainfall amounts with this system and
model qpf is likely very much underdone in those areas. There is
also the convective factor that will add some variability to the
totals. Instability parameters are pretty marginal but we're
already seeing some lightning closer to the upper low and with
these tropical systems convection is almost always a possibility.
Overall forecast remains largely intact. Models might be a few
hours slower with the arrival and I don't really see much chance
of precip across Ventura/la counties at least during the daylight
hours today. Flash flood watches for burn areas look good given
the high pwats and the potential for thunderstorms.
***From previous discussion***
Conditions look marginally favorable for some tstm activity
with the front tonight and early Fri, especially across slo and
sba counties. Rainfall rates may reach one half to two thirds of
an inch per hour during the peak of the storm, especially from the
mountains of wrn vtu County northward through slo County. With
a threat of heavy rain even making it to l.A. And ern vtu counties,
a Flash Flood Watch is in effect for the recent burn areas.
Lingering moisture will keep a chance of showers in most areas
behind the front Friday afternoon and evening, with a slight
chance of showers lingering into early Sat across the central
coast as a weak vort pushes into that area Fri night.
Heights will rise a bit across the region on Sat, and skies will be
partly cloudy. After a rather cool Friday, expect several degrees
of warming in most areas on Saturday, with Max temps in the warmer
valley locations possibly reaching 80 degrees.
Another upper low will approach northern California Saturday
night, then move across far northern California on Sunday.
Its associated frontal system may bring some rain or showers to
the region late Sat night through Sunday evening, but at this
point, it does not look as though rainfall will be too
significant. There will be several degrees of cooling across the
area on Sunday. A weak upper ridge will bring dry weather on
Monday with seasonable temps. Another upper low will move into
central California Tuesday. Models have trended stronger and
farther south with this system. They now show its frontal system
bringing rain to most areas Tuesday into Tue night, with moderate
amounts of rain possible in some areas. Once this system moves
east, dry weather is expected for Wed.
At 1700z at klax there was no marine layer. There was a surface-
based inversion with a top near 1400 ft and a temp of 21 deg c.
Moderate confidence in coastal tafs with a 30 percent chc of IFR
conds 06z-15z Friday...with 10 percent chc of LIFR during this
time. Moderate to high confidence in Vly and inland tafs with
MVFR conds expected after 12z Friday.
Rain will reach San Luis Obispo County by around 22z...ksba by
28/00z and la County by 12z Friday. Times may differ by 1-2 hours
from taf times.
Klax...moderate confidence in 18z taf with a 30 percent chc of
IFR cigs 12z-16z and a 10 percent chc of LIFR cigs 12z-15z. Light
rain with VFR cig/vis could fall as early as 06-10z.
Kbur...good confidence in 18z taf. Light rain with VFR cig/vis
could fall as early as 08-10z. 10 percent chance of IFR conds
Good confidence that conditions will remain below Small Craft Advisory levels
through Saturday. However, brief localized small craft wind gusts
are possible along and just ahead of a cold front moving through
the waters from west to east this afternoon into Friday. Moderate
to heavy rain with a slight chance of thunderstorms are expected
with a cold front moving west to east late Thursday into Friday.
A long period south swell originating from Hurricane Seymour
combined with a building long period northwest swell originating from a
low over the North Pacific may bring Small Craft Advisory for hazardous seas to the
coastal waters as early as late Saturday and more likely Sunday
into Monday across the outer waters.
California...Flash Flood Watch in effect from 3 PM PDT this afternoon
through Friday morning for zones 34-35-37. (See laxffalox).
Flash Flood Watch in effect from 9 PM PDT this evening
through Friday morning for zones 36-39-52-53. (See laxffalox).
Flash Flood Watch in effect from late tonight through Friday
morning for zones 40-45-46-54-59-547-548. (See laxffalox).