Scientific Forecaster Discussion
fxus66 klox 172046
Area forecast discussion
National Weather Service Los Angeles/Oxnard California
146 PM PDT Tue Oct 17 2017
light offshore flow will bring above normal temperatures through
today. Patchy fog and low clouds return to the coast Thursday and
Friday as temperatures cool to near normal late in the week.
Temperatures increase again this weekend and into the following
week as another offshore wind event develops over the region.
An area of elevated moisture and instability has been teasing our
outer water boundary 60-100 miles west of pt Conception all day
but as of yet no strikes within our forecast area. The moisture is
all above 650mb which is roughly 12kft and very dry below that. So
the chances for lightning are higher than receiving measurable
rain but even those are low and marginal for putting in slight
chance given the lack of easterly progress with the ridge likely
playing a role there. But will keep pops as they are for sba/slo
counties and add the Ventura/la mountains overnight as that wave
passes through the area. Can't rule out a stray storm outside
those areas, and including the coastal waters, but chances are too
low to include at this time. Again, main threat with these is the
dry lightning and possibly some brief gusty winds. Most of the
moisture and instability aloft moves east of our area after 12z so
for now no thunderstorm chances on Wed.
Gradients continue to trend onshore today and highs across most
coast/valley areas were cooler. This trend expected to continue
through the end of the week as the ridge breakdown continues and a
trough passes north of the area on Friday. Highs expected to be
back to normal by Thursday and slightly below normal Friday.
Marine lyr expected to make a partial return Thu and Fri. The
front is expected to wash out before reaching slo County so no
rain expected except possibly some North Slope showers Friday.
Issued a Wind Advisory for this afternoon for srn sb County as
northerly gradients are increasing there. Not much upper support
and winds drop off fairly quick later in the evening but should be
a good enough burst for some brief advisory level winds across the
sb South Coast zone, mainly west of Goleta. Low end wind
advisories may be needed each of the next few evenings as well,
peaking in strength Friday evening.
Northerly flow increases behind the trough passage Friday then
shifts to northeast Sunday through Tuesday. Earlier model
solutions had suggested a more southerly trajectory to the trough
but the last couple days the models have favored a more
progressive solution with less upper level support for the
offshore gradients. So this next offshore event is looking a lot
like the last one, but even warmer with a stronger ridge
developing. Temps will start warming Saturday and continue to warm
through early next week. By Tuesday, which could be the start of
the world series in Los Angeles, highs downtown are expected to
reach or exceed 100 degrees while valleys are a few degrees warmer
than that. If the current forecast holds we'll likely need heat
advisories or possibly warnings for much of la/Ventura counties
At 1800z, there was a surface based inversion at klax. The top of
the inversion was located at 1500 feet with a temperature of 28c.
Mid to high level clouds across the region today with a slight
chance of tstms this afternoon and evening across slo and sba
counties and northwest vtu County. Any tstm could produce wind gusts
over 40 kt. Except for possible brief MVFR conds in any tstms,
mainly VFR conditions are expected thru the period...except for
a small chance of marine layer cigs over coastal la County late
Klax...moderate to high confidence in the 18z taf with VFR
conditions expected thru the period...except for a 20% chance of
MVFR conds after 12z Wed.
Kbur...high confidence in the 18z taf with VFR conditions
expected thru the period...except for a 10% chance of MVFR/IFR
conds after 12z Wed.
High confidence in Small Craft Advisory level northwest winds across the outer waters
through late tonight. Small Craft Advisory winds are likely over the nearshore
waters north of Point Sal, and the western sba channel later this
afternoon through late evening, diminishing after midnight. There
is a 30% chance winds will rise to Small Craft Advisory levels over western
portions of pzz655 later today as well. Seas are expected to be
choppy throughout the waters. Winds should drop below Small Craft Advisory levels
by dawn Wednesday in most areas - but will likely increase again
by Wednesday afternoon to moderate to strong speeds through the
period. An upper disturbance will bring a slight chance of tstms
to portions of the waters from western pzz650 and northwestward.
There will be a chance of gales across the outer waters late
Thursday through Saturday, with Small Craft Advisory conditions likely nearshore.
A large storm off western Canada will generate 40 foot seas in
that area. This will produce a large long-period northwest swell, moving
into our waters by Friday. Seas up to 15 feet are likely, with 20
foot seas possible across the outer and northern waters. There
will likely be dangerous breaking waves on the central coast
through the weekend with dangerous conditions in/near harbors.
Fire weather...17/945 am.
Elevated fire danger will continue across much of southwest
California through this evening as weak offshore flow continues
to bring very warm and dry conditions...with widespread single digit
humidities today away from the immediate coast. Some lightning
strikes have been detected well off the coast of Point Conception
this morning associated with a weak upper level disturbance and
increasing subtropical mid level moisture. As this system passes
over our area this afternoon and tonight, there is a slight chance
of thunderstorms across San Luis Obispo, Santa Barbara, and
western Ventura counties. Due to the very dry lower levels of the
atmosphere, any storms that develop will be capable of producing
isolated dry lightning strikes and gusty erratic downdraft winds.
Gusty sundowner winds are expected to impact southern Santa Barbara
County much of this week, during the late afternoon and nighttime
hours. Later this afternoon and evening, wind gusts between 35 and
45 mph with humidities falling into the teens will bring elevated to
brief critical fire weather conditions across the Santa Ynez range and
Santa Barbara South Coast. In the wake of a passing upper level
trough, there is the potential for stronger sundowner winds Friday
night into Saturday evening.
From Sunday through next Tuesday, there is the potential for a prolonged
duration of gusty Santa Ana winds with hot and very dry conditions. While
there is still some uncertainty with the strength of this upcoming
Santa Ana event (which will depend on the upper level wind support),
there will be the potential for at least moderate Santa Ana winds,
triple digit heat, and humidities falling into the single digits and
lower teens which could bring a return of critical fire weather
conditions to portions of southwest California.
California...beach hazards statement in effect from Friday morning through
Friday evening for zones 34-35. (See laxcfwlox).
Wind Advisory in effect until 10 PM PDT this evening for
zones 39-52. (See laxnpwlox).
Beach hazards statement in effect through Wednesday evening
for zones 40-41. (See laxcfwlox).
Pz...Small Craft Advisory in effect until 3 am PDT Wednesday for
zones 645-650. (See laxmwwlox).
Small Craft Advisory in effect until 6 am PDT Wednesday for
zones 670-673-676. (See laxmwwlox).
Hazard potential outlook...(fri-tue)
hot temperatures and elevated fire weather conditions are
expected Sunday into early next week as another Santa Ana wind
event develops. Large surf is possible at central coast beaches
between Friday and Sunday. Strong rip currents are possible.