Scientific Forecaster Discussion
fxus66 klox 110007
Area forecast discussion...updated
National Weather Service Los Angeles/Oxnard California
407 PM PST sun Dec 10 2017
Updated aviation section
Gusty offshore winds, warm afternoon temperatures, and dry
conditions will persist into next week. Smoke from the fires will
impact regional air quality into next week as well.
Minimal changes in the weather through mid week. High pressure
along the West Coast will dominate the upper levels while a strong
surface high sits over the Great Basin. There is very little upper
support so while offshore gradients are decent (5-6mb offshore
lax-dag) by themselves they shouldn't be enough to generate
advisory level winds. Today was even a struggle with only a few
places managing very marginal criteria. And Monday looks weaker.
So will allow advisories to expire on schedule this afternoon and
not do any extension at this time. Expecting northeast winds most
areas of la/Ventura counties to stay in the 15-25 mph range this
week with some stronger mountain gusts at times.
Temperatures will continue to be 10-15 degrees above normal for
most areas. The exceptions being areas that have extremely thick
smoke coverage, mainly slo/sba counties. Some of those areas saw
10-20 degree temperature drops from yesterday with the increase in
thick smoke obscuring the sun, especially the central coast.
If the smoke manages to thin out even a little that could have a
pretty dramatic impact on temperatures so the forecast highs for
those counties are tricky and largely smoke dependent. But the
smoke models seem to indicate thick smoke there through Monday as
the winds aloft remain out of the southeast.
Not much change Thu, then Fri the ridge breaks down as a trough
moves through the pac northwest and into The Rockies. So expecting a
cooling trend Friday as gradients may actually turn briefly
onshore for the first time in several days, though still 5-10
degrees above normal. Earlier models had indicated more of a
southerly trajectory to the trough that could potentially bring a
more offshore flow over the weekend but today's solutions were
more progressive in moving it east and thus less cold air over the
Great Basin and weaker offshore flow. So for now looking at a
slight warming trend over the weekend but just light offshore
At 00z, there was no marine inversion at klax.
VFR conditions are expected throughout the period, except for a
chance of MVFR conditions in smoke at coastal and valley
terminals north of kntd. Periods of moderate low-level wind shear
and turbulence are possible Ventura County terminals through 08z.
Klax...VFR conditions are expected throughout the period. Any
east winds should remain less than 7 knots.
Kbur...VFR conditions are expected throughout the period. No wind
issues are expected at this time.
For the inner waters south of Point Conception, winds currently
just above Small Craft Advisory levels, and this should continue
through 6 PM this evening. The strongest winds will likely be
near shore between Ventura and Santa Monica.
Elsewhere, winds and seas are expected to remain below Small
Craft Advisory levels through Wednesday. There is a 20 percent
chance of Small Craft Advisory levels winds for the northern outer
waters Tuesday night into Wednesday and Wednesday night into
There will also be areas of smoke from the Thomas fire over
portions of the coastal waters through at least Sunday night,
especially from around Point Conception through to the Santa
Barbara Channel. Local visibilities could possibly drop below one
nautical mile at times.
Fire weather...10/100 PM.
Another critical fire weather day for many areas along with heavy
smoke impacts west of the Thomas fire. Red flag warnings were
extended for Los Angeles and Ventura counties through Monday 8 PM
and Santa Barbara County mountains until 6pm today. Large plume
development and very low humidity was the main reasoning for
extending the warning in sba co. Today.
Wind gusts up to 45 mph have occurred today in the windier canyons
and passes of Los Angeles and Ventura counties with widespread
humidities between 3-12 percent. Expect winds to slowly decrease
tonight, but remain locally gusty when diurnal Santa Ana's uptick
toward Monday morning. Speeds should be less strong on Monday
(gusts 30-40 mph) with lax-dag pressure gradients near -6mb or
about 1mb weaker than today. Unfortunately there will be a repeat
of poor overnight humidity ranging from 10-25 percent and many
areas returning to less than 10 percent during the day on Monday.
Temperatures will remain well above normal on Monday which could
lead to additional large plume growth over existing fires in a
deep mixing layer. There is a possibility of an extended red flag
in Santa Barbara County on Monday.
Low daytime humidity and poor overnight recoveries are likely to
persist across the entire fire district through Thursday. Santa
Ana wind speeds are predicted to be weaker Monday night into
Tuesday, but there could be local gusts in valleys and mountains
close to red flag warning criteria. Still too early to say red
flags will not be needed then. Long range forecasts show a slight
increase in onshore flow and humidities arriving (hopefully) on
Friday and Saturday. No rain possibilities expected over the next
10 days though.
If fire ignition occurs, very rapid spread and extreme fire
behavior is likely. Those near current wildfires need to stay
aware of and follow official evacuation orders. Everyone needs to
exercise extreme caution when handling any potential fire ignition
sources...such as campfires, cigarettes, welding and brush
California...red flag warning in effect until 8 PM PST Monday for zones
240-241-244>246-253-254-288-547-548. (See laxrfwlox).
Red flag warning in effect until 6 PM PST this evening for
zone 252. (See laxrfwlox).
Pz...Small Craft Advisory in effect until 6 PM PST this evening
for zones 650-655. (See laxmwwlox).
Hazard potential outlook...(wed-sun)
Critical fire weather conditions and locally gusty offshore winds
could continue into early next week.