Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Los Angeles/Oxnard California
932 am PST Fri Dec 2 2016
moderate to strong Santa Ana winds will flow through portions of
Ventura and Los Angeles counties through Saturday. Portions of
Santa Barbara County will have breezy winds. Temperatures will be
below normal for at least the next week but will warm slightly
during the next few days with Sunday as the warmest day.
The main story for the next couple days will be the strong winds
expected across much of Los Angeles and Ventura counties. A 1035
mb surface high will develop over northern Nevada behind an
inside slider that moved over the forecast area yesterday. What
will drive this stronger and colder event will be the upper level
pattern set up. A cold upper level trough will drop south from
the Great Basin into northern baja this morning. The position of
the upper low will be conducive for bringing good upper lvl support
from 850 mb to 500 mb of north to northeast flow. Also, the colder
dense air from the low will bring additional subsidence over the
area. Therefore besides being a cooler Santa Ana it should be more
widespread affecting more areas. High wind warnings are in effect
for the la/vtu County mountains and Santa Clarita valley, and also
added the Ventura County valleys where gusts to 60 mph and or
sustained winds of 40 mph will be strongest across the eastern
portion. The northwest portion of the San Fernando Valley including
Northridge to Chatsworth could see local gusts to 60 mph as well
late this morning into this afternoon. Will be adding a Wind
Advisory for Catalina Island as well. Avalon Harbor could be
affected with choppy seas from the offshore winds making it
difficult for boats in The Harbor. Unlike most Santa Ana winds,
this one will actually strengthen as we go through this
afternoon...before winds diminish some late this afternoon or
early evening. Winds will then restrengthen again tonight into
Saturday morning. There will continue to be good cold air
advection tonight to help winds remain fairly strong, while the
upper level pattern weakens slightly as the low moves further southeast
over Mexico. Offshore winds will continue into Sunday morning, but
will be much weaker and less widespread. The upper level support
will not be a factor. There is still a chance that a few low end
wind advisories might be needed for the usual wind prone areas of
Gusty offshore winds will also continue across the central coast
from the san Lucia mtns through the Sunday. Winds will be much
weaker compared to la/vtu counties.
Red flag warnings are also in place during the high wind event.
Read the fire weather discussion below for more details.
As far as temps...today will be much cooler across interior areas
while coast and coastal valleys will be 2-4 degrees cooler with
highs only reaching the mid 60s, while inland valleys and the
Antelope Valley remain cool in the upper 40s to mid 50s. Much
cooler in the mountains. For Saturday, the air mass will modify a
bit warmer and that will translate to highs 3-7 degrees warmer,
yet will still only reach the mid to upper 60s with a few 70s for
warmest la/vtu valleys. Still much cooler inland. Highs will even
warmer on Sunday as high pressure aloft nudges in from the west
and weaker offshore flow expected. Highs will bump up an
additional 3-6 degrees in most areas with inland areas seeing the
best warmup. Highs will be warmest valleys will be in the lower to
mid 70s with 60s in most all other areas...except for the
mountains which to no surprise will be much cooler.
The upper ridge that is expected over the region on Sunday will be
short lived as another trough with an inside slider drops into
the Great Basin early next week. Models have backed off any chance
of precip to the northern portion of the forecast area. The trough
will bring cooler temps ranging 4-10 degrees cooler with onshore
flow across coast and valleys. More northerly winds will develop
across sba mtns, I-5 corridor and Antelope Valley will develop as
the trough passes to our east Monday night into Tue both models
show an upper level ridge building over the state around mid week
for a warming trend with prolonged weak/moderate offshore flow.
At 1550z, there was no marine inversion at klax.
Through the taf period, VFR conditions will continue for all taf
sites. Strong northeast flow through the period will create gusty
surface winds (especially across Ventura and Los Angeles
counties). Additionally, there will be areas of moderate low level wind shear and
Klax...high confidence in VFR conditions through the period.
Moderate confidence in wind forecast as there is a 40% chance of
north to northeast winds exceeding 10 knots through this
afternoon and again Saturday morning. Low level wind shear will be likely through
Kbur...high confidence in VFR conditions through the period.
Moderate confidence in wind forecast as gusty northerly winds will
erratically surface through this evening. Low level wind shear and turbulence will
be issues through the taf period.
For the outer waters, moderate to high confidence in current
forecast. High confidence in Small Craft Advisory (sca) level
winds continuing through tonight, except through Saturday
afternoon across eastern sections of the southern outer waters.
Winds will flirt with Small Craft Advisory levels through Sunday then likely
increase to Small Craft Advisory levels Sunday night through Tuesday.
For the inner waters, moderate to high confidence in current
forecast. For the waters north of Point Sal, winds and seas are
expected to remain below Small Craft Advisory levels through Tuesday. For the
waters south of Point Conception, high confidence in gale force
winds through this evening with Small Craft Advisory level winds expected tonight
and Saturday. The strongest winds will occur from Ventura to Santa
Monica (out to anacapa and Santa Cruz islands) and through the San
Pedro Channel (out to Catalina island).
Fire weather...02/900 am.
Strong upper level flow coupled with high pressure over the Great
Basin will continue to produce a strong Santa Ana wind event to
Los Angeles and Ventura counties through Saturday. Though much of
the area has received around 1 inch of rain over the last two
weeks, the vegetation (fuels) remain receptive to large fire
growth under red flag weather conditions.
Over the coastal and valley areas (including the Santa Monica
mountains), humidities will generally lower into the 10 to 15
percent range today and 8 to 12 percent range on Saturday.
Red flag conditions are expected this afternoon through Saturday
afternoon as a result. Red flag warnings are in effect for
coastal and valley areas of vtu and l.A. Counties through Sat
Over the mountains, the cold temperatures will keep relative
humidities generally above 20 percent today, but should lower
into the 10 to 20 percent range on Saturday. As a result, the
mountains will not have a red flag warning today (though there is
an elevated risk with the strong winds) but the Los Angeles County
mountains will be under a warning on Saturday. With weaker winds
and the same humidity issues, the Ventura County mountains will
remain out of the red flag warning.
Those handling potential fire ignition sources must exercise
extra caution as extreme fire behavior and rapid fire growth is
expected if any fire were to be started. This includes those
lighting fires for warmth considering the cold conditions.
California...freeze watch in effect from late tonight through Saturday
morning for zone 37. (See laxnpwlox).
Wind Advisory in effect until 2 PM PST Saturday for zones
40-41-87-547. (See laxnpwlox).
High Wind Warning in effect until 2 PM PST Saturday for zones
44>46-53-54-88. (See laxnpwlox).
Wind Advisory in effect until 6 PM PST this evening for zone
59. (See laxnpwlox).
Red flag warning in effect until 6 PM PST Saturday for zones
240-241-244>246-288-547-548. (See laxrfwlox).
Red flag warning in effect from 6 am to 6 PM PST Saturday for
zone 254. (See laxrfwlox).
Pz...Gale Warning in effect until 9 PM PST this evening for zones
650-655. (See laxmwwlox).
Small Craft Advisory in effect until 3 am PST Saturday for
zones 670-673. (See laxmwwlox).
Small Craft Advisory in effect until 2 PM PST Saturday for
zone 676. (See laxmwwlox).
Hazard potential outlook...(sun-thu)
no significant hazards expected.