Scientific Forecaster Discussion
Southwest California area forecast discussion...updated
National Weather Service Los Angeles/Oxnard California
800 PM PDT sun Mar 9 2014
A weak upper trough will pass to the north Monday brining continued
middle to high clouds and slightly cooler temperatures to the region.
High pressure will build from the west while an upper low approaches
from the northeast by Wednesday. This should bring Santa Ana winds
to the region by Tuesday and continue through middle week and will
raise temperatures above normal across coast and coastal valleys.
Short term (tonight-wed)...evening update...
As expected...a few record high temperatures occurred this afternoon. La
Airport (lax) climbed to 85 degrees breaking the old record of 82
degrees set this day 2 years ago 2012. Long Beach was able to tie
the previous record for this day from 2004 at 87 degrees. And
lastly...Santa Maria broke the old daily record of 83 degrees set in
2004 with a high of 86 today. The combination of a day 2 Santa Ana
wind event...(not as strong as yesterday)and a upper ridge axis
overhead allowed for the continued warmer than normal conditions.
There were reports that at least 22 runners from the la Marathon had
to be treated for heat illness. Most Los Angeles beach areas warmed
up to the middle and upper 80s. In fact it was quite warm across all
beaches from Los Angeles County to San Luis Obispo County...where
there were plenty of +80 degree temperatures recorded this afternoon.
It was so warm in the San Fernando Valley today...that a west wind
that usually develops in the far western sfv on hot days pushed east
through Van Nuys and into Burbank today. Very rare for an early
With the change to daylight savings time...there was an hour delay
receiving latest 00z NAM-WRF run. However...it is in now...and there
is little change from the earlier 18z run which indicated a very
strong and potentially damaging Santa Ana wind event beginning
Tuesday evening through Wednesday evening...with the peak occurring early Wednesday
morning through middle afternoon. Otherwise...forecast looks to be
on track so no updates expected this evening.
***From previous discussion***
Expect a mixture of middle and high clouds continue to move across
southwest California on the southern edge of an atmospheric river stretching
from Hawaii to northern California. This storm system will shear apart
tomorrow with no rain making it this far south. We will have light
offshore flow in the morning before winds turn onshore and cool most
valleys and coasts compared to today. Additional cloud cover from
the dissipating frontal system will also keep temperatures more in
check on Monday.
A low pressure system will move into the central rockies by Tuesday
morning and then dives southward to Arizona by Wednesday morning. A
1035mb or stronger surface high pressure builds in behind the low
across the Great Basin. All aspects of a strong Santa Ana wind event
are shown on the high resolution NAM model...cold advection...
surface pressure gradients...and alignment of upper level winds.
However...the GFS/Gem show much less wind potential by keeping the
low pressure system more to the north. The European model (ecmwf) model is somewhere
in-between. We have trended the forecast toward the stronger NAM
model but confidence is not high as the other models are in
disagreement. Either way it will be windy and dry with elevated fire
weather concerns when this event comes together. Offshore winds
start across eastern Ventura and western Los Angeles counties
early Tuesday morning...peaking Wednesday morning and remaining
breezy into Thursday morning. Peak wind gusts could easily reach
50-60 miles per hour in the mountains and be closer to widespread 70 miles per hour gusts
if the NAM model verifies. Humidities will be very low and
temperatures will be 5-15 degrees above normal across coastal areas
during the Santa Ana event.
Long term (thu-sun)...
weak northwest flow aloft will be over southwest California Thursday-Friday and the
last part of the Santa Ana will wrap up Thursday morning. Weak
onshore flow returns briefly on Friday for the coolest day of the
extended period. The main story in the long term is a continuation
of dry conditions and good model consistency of building high
pressure across the entire state for next weekend. Heights build to
587dm by Sunday. Would expect another very warm weekend with a few
record temperatures in the 80s to near 90 possible once again.
on Tuesday...gusty northeast winds are expected to redevelop across
Southern California with humidities falling to between 10 and 15
percent in the afternoon. Later Tuesday night through Wednesday
night...there is the potential for a stronger Santa Ana wind
event...however there remains considerable discrepancies between
computer model runs. The high resolution NAM model is the strongest
model solution at this point with a projected lax-Daggett gradient
of -7.5mb by 12z Wednesday. In addition...the NAM model has
impressive upper level wind and thermal support. Preliminary wind
gust estimates during the peak of this wind event are expected to
range between 50 and 60 miles per hour across the mountains of Los Angeles and
Ventura counties...with gusts in the 40 to 50 miles per hour range across
coastal and valley areas. However...it is important to stress that
even stronger winds are possible with this system if all the
necessary parameters come together. Meanwhile humidities will lower
to between 10 and 15 percent across much of the region on
Wednesday...with isolated single digit readings possible. The
combination of gusty offshore winds and low humidities will bring
elevated fire danger to Southern California Tuesday through
Wednesday night. A Fire Weather Watch may need to be issued for this
event as critical fire weather conditions would be met if the
computer models continue to trend towards the stronger NAM solution
for Tuesday night into Wednesday night. Offshore winds are expected
to diminish on Thursday...but there is the potential for a very warm
Santa Ana wind event next weekend.
High confidence in the 00z tafs. Expect VFR conditions through the
period...except 40% chance for MVFR visibilities for the central coast
sites between 12z-17z Monday.
Klax and kbur...high confidence in the 00z taf. There will be plenty
of middle to high level clouds through the next 24 hour period.
high rip current risk (see laxsrflox).