Area Forecast Discussion
Issued by NWS Los Angeles, CA
FXUS66 KLOX 301120
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
420 AM PDT SAT APR 30 2016
A low pressure system moving through the Great Basin will produce
gusty winds and a slight chance of showers and thunderstorms for
parts of the area through the weekend. Warmer weather is expected
early next week as weak high pressure builds over the region, but
another low pressure system could bring showers and cooler
conditions to the area late next week.
The latest infrared imagery shows a trough of low pressure
spinning counter-clockwise over the Owens Valley this morning.
This trough will continue to dig into the Lower Colorado River
Basin this afternoon. At the surface, a Catalina eddy remains
intact over the Southern California Bight. Fog product imagery
indicates a deep marine layer in place with stratus filling in
over the South Coast Basin and the Bight. The latest KLAX AMDAR
soundings from 07Z show a marine layer depth up to around 2800
feet, but with satellite inspection, it has deepened to around
3000 feet since 07Z.
A vorticity maximum associated with the trough is currently
located over the San Joaquin Valley. This vort max will drop south
into Los Angeles County later this morning. Instability with the
feature will develop patchy morning drizzle this morning and
possibly some isolated showers across Los Angeles County and the
Ventura County Mountains. An unstable air mass will remain over
Southern California region through this evening, and with daytime
heating, the atmosphere will destabilize. Isolated to scattered
showers and isolated thunderstorms are forecast for this afternoon
and evening across mainly the interior portion of Los Angeles
County. Persons planning outdoor activities, especially in the
foothill areas, mountains, and desert in Los Angeles County today
should make contingency plans due to the possibility of
thunderstorms. Motorists should also plan for wet roadways,
especially those traveling into the mountains and desert. There is
also a potential for snow above the 7000 foot elevation.
A marginal wind advisory also remains in effect through this
evening for the Los Angeles and Ventura County Mountains and the
Antelope Valley. Model solutions are trending lighter with the
winds for this afternoon and evening, and there is a chance that
the advisory could be cancelled early. Dynamic features are still
in place to support a wind advisory with stronger winds aloft, but
low-level wind support is starting to wane. High confidence exists
in marginally gusty winds through this morning. Confidence is
lower for the afternoon and evening hours.
The broader trough will remain over much of the West into early
Monday and keep a cooler air mass in place. A deep marine layer
will also remain for areas south of Point Conception. Enough
instability remains to keep at least isolated showers and
thunderstorms for Sunday afternoon and evening over the Los
Angeles and Ventura County Mountains and the Antelope Valley.
The broad trough should start to exit the region on Monday and
allow for weak ridging aloft to build in from Monday evening through
Tuesday. 500 mb heights are bit lower than previous model runs. A
warming trend remains in the forecast, but temperatures look
closer to seasonal to slight above normal for Tuesday.
Southwest flow aloft should start to establish throughout the day
on Tuesday and increase in strength Wednesday. Model solutions, in
agreement over the last 24 hours, are starting to vary on the
movement and timing of the trough. ECMWF model solutions have been
most consistent with GFS solutions starting to vary. 06Z GFS
solutions are closer to the 00Z ECWMF solutions, and thus,
preference is given to the ECMWF model. With model trends and
consistency of the ECMWF solutions, PoPs remain unchanged for most
part and keep a slight chance to chance of showers in the
forecast from Thursday through Saturday. There is a chance that
the arrival could be as early as Wednesday afternoon or evening
and the exit of the trough could delay until Saturday night or
maybe Sunday. A cool and showery weather pattern should be
expected for the latter half of next week.
Marine layer at LAX at 2300Z is 3500 feet deep and the inversion
top is at 5500 feet with a temp of 11.4 degrees C.
Another cold upper level low pressure system will dig
southeastward across interior California tonight into Saturday.
This system will reinforce the upper level northwest winds
across the forecast area. Closer to the surface...strong onshore
flow and an eddy circulation will maintain a deep marine layer
pattern into Saturday, with low clouds and fog spreading into
most coastal/valley areas. Gusty winds vcnty KSBA will generate
moderate uddfs and llws this evening.
KLAX...SCT-BKN015 conditions through the early evening hours
then MVFR cigs likely tonight into Saturday morning, with a
30 percent chance of cigs lingering into the afternoon hours.
Eddy circulation will generate se-e winds 5 to 8 knots overnight
into Saturday morning, with a 20 percent chance of reaching 10
KBUR...High probability of mvfr cigs reaching KBUR overnight into
Good confidence that gales will persist across the outer waters
through this evening, although winds may drop off a bit for a few
hours this morning. Then, good confidence that winds will drop
below gale levels by late evening, with winds and seas likely
below SCA levels by daybreak Sunday.
Across the Sba Channel, SCA level winds across western portions
should diminish below SCA levels by mid morning. There is a 20 to
30 percent chance of SCA level winds across western portions
from mid to late afternoon through mid evening. Across the
northern inner waters, fairly high confidence in SCA levels from
this afternoon through mid evening.
After tonight or early Sunday, winds are expected to be rather
light across the waters through Wed. A long period Southern
Hemisphere swell will move into the waters today, building to
2 to 4 feet at 16 to 18 seconds by Sunday. This long period swell
will likely cause strong currents and surging, along with
shoaling in shallow water.
CA...Beach Hazards Statement in effect through Sunday evening For
zones 34-35. (See LAXCFWLOX).
Beach Hazards Statement in effect from 8 AM PDT this morning
through Sunday evening For zones 40-41-87. (See LAXCFWLOX).
Wind Advisory in effect until 8 PM PDT this evening For zones
53-54-59. (See LAXNPWLOX).
PZ...Small Craft Advisory in effect until 9 PM PDT this evening
For zone 645. (See LAXMWWLOX).
Small Craft Advisory in effect until 9 AM PDT this morning
For zone 650. (See LAXMWWLOX).
Gale Warning in effect until 9 PM PDT this evening For zones
670-673-676. (See LAXMWWLOX).