Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Southwest California area forecast discussion 
National Weather Service Los Angeles/Oxnard California
440 am PDT Sat Aug 23 2014

..aviation discussion updated...


A trough of low pressure over California will result in a cooling
trend through Monday with night through morning low clouds and fog.
A significant warming trend is expected through the rest of next
week as high pressure develops. Low clouds and fog will be limited
to coastal areas with possibilities of dense fog next week.


Short term (today-mon)...latest acars sounding near lax indicated
the marine layer depth around 1800 feet this morning. The onshore
surface gradient between lax-dag was trending over +3 mb stronger
this morning compared to 24 hours ago. What that meant was a quicker
surge of low clouds over the coastal areas and into the valleys
before midnight. Latest fog product showed most areas west of the
la/vtu County mountains filling in nicely. Expect low clouds to scour out
early in the valleys...and by middle to late morning for the la County
coast. With the inversion relatively strong today...low clouds could
linger along the beaches of Ventura and sba County South Coast
through at least middle afternoon. High temperatures should continue to trend
cooler by a few degrees today through Monday as a broad upper level
trough will continue to linger over California through Monday.
Expect night through morning low clouds to continue through at least
Monday morning for coast and coastal valleys. The marine layer depth
will lower to around 1000 feet by Sunday night into Monday morning.

Some high clouds from tropical storm could move over the region S of
Point Conception Monday/Monday evening. Speaking of Tropical Storm
Lowell...high surf will continue to affect south facing beaches
across ls/vtu counties through Sunday afternoon. Maximum surf to 9
to 10 feet can be expected.

Long term (tue-fri)...
by Tuesday a relatively strong upper high off the coast of Oregon
and weak high pressure off the Baja California coast will merge as the upper
trough pushes east of the region. The upper ridge will strengthen
over California on Tuesday. The combination of this strong ridge over
the area and weaker onshore gradients Tuesday will allow for the marine
layer to shrink considerably leaving stratus limited to coastal
areas. High temperatures will increase significantly from Monday as well.
By Wednesday...Hurricane Marie will have some influence on our
weather as it is expected she will be around 700 nm south-southwest of Los
Angeles. Not with rain...but with weak offshore flow due to the
proximity of the hurricane. With strong high pressure remaining
aloft and weak offshore flow expected...high temperatures will continue to
rise Wednesday and Thursday and the low clouds could be held offshore for a
couple days...or at the least some dense fog could be possible for
the immediate coastal areas night through morning hours through the
extended period. By Friday the GFS and European model (ecmwf) models begin to differ
some. The GFS is showing a more progressive upper trough pushing
down the Pacific northwest while high pressure continues to linger over
California. If the GFS is correct..expect remnants from what use to
be Hurricane Marie to get drawn in by the trough as it approaches
northern California. GFS does bring a decent amount of rain to areas north of
San Francisco...with lighter amounts as far south as slo County.
While not expecting showers or thunderstorms at this point...if the
hurricane moves any closer to shore it would move into the realm of
possibilities. A large south swell is also likely with the storms



moderate confidence in 12z taf package with the reduced confidence
due to the uncertainty regarding timing and extent of the marine
intrusion. LIFR-IFR conditions at taf sites from ksba northward
along the coast this morning. IFR-MVFR conditions at taf sites from
koxr southward and also at the San Fernando Valley taf sites.
Conditions will clear along the coast 17z-20z and inland 15z-17z.
Kprb will have LIFR-IFR conditions through 17z. Similar conditions
will redevelop tonight and some locations will have only a few hours
of clearing. Otherwise and elsewhere VFR conditions will prevail.

moderate confidence in 12z taf package with the reduced confidence
due to the uncertainty regarding timing and extent of the marine
push. LIFR-IFR conditions will continue through 17z-20z then return
03z-06z and continue until 17z or later tomorrow morning. Otherwise
VFR conditions will prevail.

moderate confidence in 12z taf package with the reduced confidence
due to the uncertainty regarding timing and extent of the marine
push. MVFR conditions will clear 15z-17z then redevelop 07z-09z.
Otherwise VFR conditions will prevail.

Marine...23/300 am.
Southerly swell 4 to 7 feet from Tropical Storm Lowell will continue
to impact the coastal waters through the weekend.

Hurricane Marie will follow a similar track to Lowell which would
bring an even larger swell to the region. A long period southeast
swell (150 to 160 degrees) is expected to build across the Southern
California coastal waters on Tuesday and Tuesday night. The swell
is expected to peak on Wednesday into Thursday... with heights
generally ranging between 7 and 10 feet across the coastal waters.
The swell direction is gradually forecasted to shift to a southerly
direction during this time frame.


Beaches...23/300 am.
A high surf advisory is in effect through Sunday afternoon for south
facing beaches of Los Angeles and Ventura counties... with large
surf accompanied by dangerous rip currents. Reports have generally
shown peak surf heights in the 5 to 7 foot range across south facing
beaches... however Port Hueneme reported breakers up to 10 feet late
on Friday. This surf event originated from Tropical Storm Lowell and
is expected to remain high through Sunday morning.

Confidence is growing that Hurricane Marie will continue to
intensify and move northward in a similar path to Lowell. There is
the potential for a significant surf event for south and southeast
facing beaches with maximum sets of 10 to 13 feet possible. If this
occurred it would be one of the strongest southerly surf events in
the recent past. Confidence in the track and intensity of Hurricane
Marie will increase notably by early next week.


Lox watches/warnings/advisories...
high surf advisory (see laxcfwlox).
High rip current risk (see laxsrflox).




National Weather Service Glossary of Abbreviations