Scientific Forecaster Discussion
Southwest California area forecast discussion
National Weather Service Los Angeles/Oxnard California
215 PM PDT sun Mar 9 2014
slightly cooler weather and an increase in clouds is expected early
next week as a trough approaches from the north. Gusty offshore
winds should return to much of the area by early Tuesday and peak on
Wednesday...along with a warming trend through the second half of
Short term (tonight-wed)...
main concern is a potentially strong Santa Ana Tuesday night into
Another warm day as onshore winds have been slow to materialize and
remain out of the south-southeast at 21z. Lax had at least tied a
record high at 82 degrees and most of the warmest temperatures were
at the beaches. 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.
High confidence in the 18z tafs. Mainly VFR conditions are expected
through the period...except for the central coast sites where MVFR
ceilings are expected between 12z-18z Monday. East winds along the
Ventura/l.A. Coast will shift to onshore by 20z-22z this afternoon.
Klax...high confidence in the 18z taf. There is a 10% chance that east
winds could increase to 10 knots before shifting to onshore by 20z.
There is a 20% chance the timing of shift to onshore flow will
differ by +/- 1 hour from taf time.
Kbur....high confidence in the 18z taf.
high rip current risk (see laxsrflox).