Scientific Forecaster Discussion
fxus66 klox 192101
Area forecast discussion
National Weather Service Los Angeles/Oxnard California
201 PM PDT Thu Sep 19 2019
An upper level trough passed through the area on Thursday. Gusty
north to northeast winds will accompany the warmer and drier air
in some areas. This warming pattern will continue through Monday
- when the next upper level low approaches.
Short term (tdy-sun)...19/141 PM.
A trough that has moved into the Great Basin today isn't having
much impact locally except increasing northerly winds across the
western portion of sb/slo counties. Another round of generally low
grade sundowners expected this evening, mainly west of Goleta and
San Marcos Pass. Will likely see advisory level gusts for a few
hours in the Gaviota/Refugio areas but elsewhere speeds should top
out in the 15-25mph range. Will hold off issuing an advisory given
the limited areal coverage and impacts. Some northerly winds
expected in these areas the next couple nights as well but tonight
should be the strongest.
Otherwise, main story next few days is the increasing offshore
flow as surface high pressure strengthens over the Great Basin.
The biggest offshore trend will be Friday morning as we go from
moderate onshore flow to light offshore flow, but gradients
continue to trend offshore through Sunday morning before
reversing as the next trough hits the pac northwest. Winds aloft aren't
impressive but typical of these early season Santa Ana events and
there will be some northeast winds surfacing in the mountains and
some of the valleys, especially la/Ventura counties and the hills
and mountains along the central coast. We likely won't see
advisory level winds with this event but it will be breezy in some
areas and warmer and drier each day with the highest temps
expected Sunday with highs near 100 in the warmer valleys and mid
80s to lower 90s for coastal areas more than a few miles inland
from the beaches.
Not much in the way of marine layer clouds next few days as
offshore flow takes over. However models insist on keeping some
very low level moisture across coastal la County next couple
mornings and in the Santa Maria/Lompoc areas. Pretty low
confidence in this part of the forecast as inversion remains
weak. Otherwise plenty of sunshine this weekend with highs
generally 4-8 degrees above normal.
Long term (mon-thu)...19/200 PM.
The Sunday trough that will begin the reversal from offshore to
onshore flow is also the feature that models have been struggling
with for next week. Today's solutions offer some hope that they
might be converging as a majority of the GFS ensembles (except the
deterministic) are in line with the European model (ecmwf) which slides the trough
towards the 4 corners and forms a closed upper low over Arizona that
briefly detaches from the westerlies Tuesday and Wednesday. This
pattern is not favorable for precip for US but is favorable for
re-strengthening of the offshore flow Tuesday. So after a one day
onshore reversal Monday and cooler temps confidence in growing on
a return to offshore flow Tue/Wed with better upper support than
we will have with the offshore event weekend. Didn't want to go
all in on this solution just yet given the models difficulties
lately but the model trends are promising in terms of confidence
Offshore flow expected to weaken Thu as the low moves east and a
new trough arrives along the pac NW, starting a cooling trend that
is expected to continue through next weekend and could eventually
bring some precip to the area.
At 1715z at lax, there was a deep moist layer up to 3500 ft with
no significant inversion.
North of Point Sal...high confidence in 18z tafs with VFR conditions
and only a 10% chance for patchy IFR fog from 10-16z.
S of Point Sal...moderate confidence in 18z tafs. Scattered clouds
through 21z for coastal terminals. Central coast sites after 08z
IFR/LIFR cigs and dense fog possible, about a 60% chance. La coast
a 60-70% chance of MVFR cigs after 10z. Remaining VFR across
valley taf sites.
Klax...moderate confidence in 18z taf. Patchy MVFR cigs until 19z,
then a 70% chance of MVFR cigs returning 10-17z. Easterly winds
not to exceed 7 knots Friday morning.
Kbur...high confidence in 18z taf. Scattered clouds through 21z,
otherwise VFR conditions continuing through Friday morning.
Moderate to high confidence in the current forecast.
For the outer waters, Small Craft Advisory (sca) level winds are
likely to persist through early Friday morning. Winds will
subside some on Friday, with a 40% chance of Small Craft Advisory gusts
redeveloping Friday afternoon into the evening. There is a 60%
chance for Small Craft Advisory gusts returning for late Sunday afternoon through
Across the inner waters north of pt sal, Small Craft Advisory wind gusts are
expected to continue into this evening. Weaker winds are expected
Friday and through the weekend.
Across the Santa Barbara Channel, Small Craft Advisory level winds are expected
across western portions of The Channel through late tonight.
There is a 20% chance for Small Craft Advisory conditions across the western Santa
Barbara Channel Friday afternoon. Otherwise, the remainder of the
inner waters should remain below Small Craft Advisory conditions through Monday.
Pz...Small Craft Advisory in effect until 9 PM PDT this evening
for zone 645. (See laxmwwlox).
Small Craft Advisory in effect until 3 am PDT Friday for
zones 650-670-673-676. (See laxmwwlox).
Hazard potential outlook (sun-thu).
On Tuesday and Wednesday, there is a chance of a Santa Ana wind
event as well as elevated fire weather conditions.