Scientific Forecaster Discussion
Southwest California area forecast discussion...updated
National Weather Service Los Angeles/Oxnard California
830 PM PST Sat Jan 24 2015
..updated marine discussion...
gusty northeast winds and high pressure aloft with bring clear skies
and well above normal temperatures through the weekend. Temperatures
will return to near normal next week...with low pressure systems
bringing a chance of showers early in the week...then again late in
Short term (tonight-tue)...evening update.
Still quite windy across a good part of Los Angeles and Ventura
counties this evening. Lax-bfl gradients (ne to SW direction) were
just under -6mb while the lax-bfl gradient (n to S direction) were
increasing to just over -6mb. This will help to keep winds more wide
spread from the I-5 corridor into a good part of the San Fernando
Valley as well as the usual wind prone Santa Ana locations. Model
guidance is a bit weaker with the northerly gradient this evening.
Strongest wind gusts were occurring across the la County mountains
and the Santa Monica Mountains with gusts in the upper 50s. Winds
will continue be fairly strong...but will lose some of the upper
support as the positioning of the upper low off the coast of Baja California
and upper high just off the northern California coast will begin to
shift clockwise around each other setting up more of a Rex block
synoptic pattern later tonight into Sunday. At the lower
levels...the pressure gradients will remain fairly strong offshore
with continued cold air advection overnight night into Sunday
morning. Therefore...at this time the high wind warnings for the
la/vtu County mountains including the Santa Monica range as well as
the Santa Clarita valley will be downgraded to wind advisories later
this evening. There will continue to be some locations that will
experience local gusts in the lower 60s overnight...but overall
expect strongest wind gusts to be in the 50s for the
mountains...while the coast and valleys will experience gusts
between 35 and 50 miles per hour through Sunday morning.
As far as today's temperatures went...a record high temperature was recorded at
Santa Maria of 82 degrees which tied the old record set back in
1935. Overall high temperatures reached the upper 70s to lower 80s across
most coast and coastal valleys...while interior valleys...Lower
Mountain elevations and the Antelope Valley were in the 60s.
Overall...only minor tweaks made from the previous shift. The latest
NAM-WRF 00z model came in and only potential change could be the
timing of the rain that is expected to move in by Monday
afternoon...south to north. Most areas will be affected Monday night
into Tuesday. Highest rainfall amounts look to be across the interior
regions as it wraps in from the south. Latest 00z NAM-WRF also
showed slightly higher rainfall amounts across interior locations.
Ranging from less than a tenth of an inch along the coast...to
around two thirds of an inch in the la/vtu County foothills and
***from previous discussion***
Strong Santa Ana wind event today across Los Angeles and Ventura
counties caused numerous downed trees and power outages. The
strongest winds occurred in the Los Angeles County mountains and
Santa monicas with the following wind gusts (malibu hills 82
miles per hour...Camp Nine at 79 miles per hour...Mill Creek at 74 mph). Much of the
Los Angeles County valleys and eastern Ventura County valleys were
also hit hard today with a peak wind gust up to 60 miles per hour at
Burbank...56 miles per hour at Tonner Canyon...and 66 miles per hour at cheeseboro.
Model cross sections showed a very impressive deep layer of strong
offshore winds and subsidence earlier today...along with good cold
air advection. The lax-Daggett gradient peaked at an impressive -7.5
mb this morning...and is currently running at -6.6 mb. Due to the
strong upper level wind support and subsidence between 850 and 500
mb...the Santa Ana event was more widespread than usual...and strong
winds in areas that normally do not see much in the way of offshore
winds. This would include areas like the foothills of the San
Gabriel valley...and much of the San Fernando Valley (including
High wind warnings remain in effect through this evening for the
mountains of Los Angeles and Ventura counties (including the Santa
monicas) as well as the Santa Clarita valley...where damaging wind
gusts over 60 miles per hour will continue to be likely. Once the wind warnings
expire...wind advisories will likely be posted through Sunday
afternoon for the mountains and Santa Clarita valley. Wind
advisories also expected to continue across much of the coastal and
valley areas...with gusts generally ranging between 35 and 50 miles per hour.
Upper level wind support and subsidence will gradually weaken
overnight into Sunday and the flow will become more easterly with
time. However...there is still a good surge of offshore winds from
the surface to 850 mb level late tonight into Sunday morning. In
fact...lax-Daggett gradient expected to peak around -7 mb on Sunday
Maximum temperatures climbed into the lower 80s today in warmer
locations...and will likely nudge up another degree or two on Sunday.
Maximum temperatures records for Sunday could be in jeopardy in a few locations
such as slo cal poly...sba Airport and Santa Maria Airport...but
most records elsewhere for the 25th are well into the 80s and will
probably be out of reach. The moderate to strong Santa Ana winds
will bring an extended period of elevated fire danger to southwest
California. Please see fire discussion below for more details.
The upper low off the Baja California coast will send increasing middle and upper
level moisture into Southern California on Monday. This system is
not expected to be a major rain producer...but there will be a
chance of rain showers from Monday afternoon through Tuesday. There
is still the question of how much rain will fall with this first
system...but high resolution NAM model does show the potential for
between .10 and .50 inches.
Long term (tue night-sat)...by Tuesday night...all extended models
show moisture with the first system moving out of the area. Partly
cloudy and cool on Wednesday...then long range models indicate
another system from the southwest potentially moving into our area
sometime between Thursday and Friday. If any rain falls with this
system...it is expected to be fairly light. Confidence in the
forecast during the entire long term period is below average.
There is no marine layer at klax this afternoon.
VFR conditions expected across all airfields through period. Gusty
northeast winds will continue to diminish gradually through the
evening hours...then expected to increase somewhat by early Sunday
morning. There is still the potential for low level wind shear tonight at klax...
Klax...VFR conditions through period low level wind shear likely above 020 between
Kbur...VFR conditions through period low level wind shear likely above 020 between
the large swell diminished enough this evening to drop the small
craft for hazardous seas zones 645/670/763. Extended the Small Craft
Advisory for hazardous seas until 3 am sun for zone 673 as 10 feet seas
continued this evening at the south Santa Rosa Island buoy. Small
Craft Advisory conditions for northeast winds from Ventura to Santa
Monica and out to the northern Channel Islands as well as the San
Pedro Channel to Avalon Harbor will continue through Sun morning. Winds
did diminish this evening well below advisory levels...but will
increase overnight with gusts up to 30 knots possible late tonight and
Sun morning...especially near shore. A low pressure system over the
western Pacific was generating seas approximately 35 feet within a
300-310 degree fetch direction. This swell is expected to arrive
beginning Thursday of next week.
Fire weather...24/300 PM...
Extended period of elevated fire danger for Southern California
this weekend due to moderate to strong Santa Ana winds...warm
temperatures...and low humidities. Minimum humidities have generally
ranged between 10 and 20 percent across much of Los Angeles and
Ventura counties today...rising to between 15 and 30 percent on
Sunday. While the strength of Santa Ana winds and low humidities
will likely exceed critical levels in some areas today...a red flag
warning will likely not be issued for this event due to the current
state of the fuels. Live fuel moisture levels have increased
significantly across much of Los Angeles and Ventura
counties...while green-up of the fine fuels has been considerable.
High Wind Warning (see laxnpwlox).
Wind Advisory (see laxnpwlox).
Small Craft Advisory (see laxmwwlox).
High surf advisory (see laxcfwlox).
High rip current risk (see laxsrflox).