Area Forecast Discussion
Issued by NWS Los Angeles, CA
FXUS66 KLOX 272055
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
155 PM PDT Thu Oct 27 2016
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.
Lots of moisture headed our way but still some uncertainties as to
how much of that will reach the ground. Pretty confidence that
areas north of Pt Conception, particularly near the coast will get
a good dose of rain with some rain rates that could approach an
inch per hour. Strong orographic enhancement there along with
pwats around 1.7" and better pva will be the big players there.
Also some possible thunderstorms will enhance rates as well.
Further south and east the confidence drops off as the last couple
days models have been trending lighter as the moisture and
dynamics slide to the north rather than progressing uniformly
through the entire forecast area. Orographics should still help
generate decent rain amounts in upslope areas and there still
should be enough instability to cause some thunderstorms to
develop, but outside of those factors most locations south and
east of SBA will likely receive less than a half inch of rain with
this system, with the bulk of it late tonight through early
No snow with this system as snow levels will be at or above 12k
feet due to its subtropical origins.
Precip will taper off in most areas by Friday afternoon with just
some lingering light showers, mainly mountains and Central Coast.
Being that this isn`t the typical northwest cold front moving
through with strong west to northwest flow behind it clouds will
likely linger longer and even Saturday could be fairly cloudy at
times. The GFS actually shows a narrow slug of moisture around
700 mb over Ventura and LA counties and a few light showers or
sprinkles can`t be ruled out. The NAM is further south with this
but still has enough moisture around to keep skies partly to
On Sunday a weak cold front will move through the area. This one
doesn`t have a lot going for it. Virtually all the energy with it
is well north of SLO county, but there could be just enough
moisture lingering from the previous system to spawn some light
showers, mainly north of Pt Conception. Temperatures will be
cooler Sunday as the weak system has a more traditional northwest
origin rather than subtropical.
The Sunday system should be out of the area by Monday morning with
clearing skies. However, a third system and cold front will move
through fairly rapidly Tuesday that should bring rain to all
areas. Pretty big differences between the GFS and ECMWF with this
one as the GFS actually has much colder air, more moisture, and
better dynamics with it. Still, the quick speed of it and limited
southerly flow will limit amounts to a half inch or less in most
Warmer and drier Wed/Thu as high pressure returns.
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 SCA 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 NW swell originating from a
low over the North Pacific may bring SCA for hazardous seas to the
Coastal Waters as early as late Saturday and more likely Sunday
into Monday across the outer waters.
CA...Flash Flood Watch in effect 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).