Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 04/28/19
Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
820 PM PDT Sat Apr 27 2019
Westerly winds will bring marine clouds, fog, and cool
temperatures into the coastal and valley areas tonight and Sunday
morning. A storm system approaches on Sunday, bringing more
clouds and a chance of mountain showers and thunderstorms. The
showers and storms will become more widespread Sunday night,
mainly south of San Luis Obispo County. Monday will be mostly dry.
.SHORT TERM (SAT-TUE)...27/818 PM.
A strong onshore flow and deep marine layer pattern brought cooler
temperatures today and greater low cloud coverage lingering into
the afternoon across many coastal plain locations. Current
satellite imagery this evening showing low clouds surging quickly
inland, with pilot reports and ACARS data showing a marine layer
depth around 2300 feet across the LA basin. As an upper level
low pressure system approaches the coast over the next 24 hours,
the marine layer is expected to lift to between 3000 and 3500
feet by Sunday morning, resulting in low clouds reaching the lower
coastal slopes, and areas of drizzle expected for locations south
of Point Conception. Would not be surprised to see a few location
receive light measurable rainfall, especially across the
foothills. Even less clearing expected on Sunday afternoon, with
an influx of mid to high level clouds moving into the area
associated with the upper low. In evening update, have tweaked
temperatures down a few more degrees in many locations on Sunday.
A few lightning strikes being picked up near the center of the
upper level closed low pressure system this evening, which is
currently centered around 550 miles WSW of Point Conception. As
the upper low tracks eastward on Sunday, there will be increasing
mid level moisture streaming into the region during the afternoon
and evening hours. During this time, there is some upper level
diffluence and instability across the mountains to warrant the
slight chance of thunderstorms over the mountains of Ventura and
Santa Barbara counties. Computer models in fairly good agreement
that upper low will track through the coastal waters off Southern
California later Sunday night through early Monday morning. During
this time, there will be colder air aloft (500 mb temperatures as
low as -20 degrees Celsius) moving over the region which will
help to destabilize areas south of Point Conception including the
adjacent coastal waters. 00Z NAM continues to highlight MUCAPE
values in the 200-500 J/kg range along with some mid level
moisture and lift, resulting in the slight chance of
thunderstorms expanding to most areas south of Point Conception
including the coastal waters where the low center will be
tracking. Rainfall with this system will likely be fairly minimal
(mostly drizzle and light rain showers with the deepening marine
layer). with Pops generally in the 20-30 percent range for areas
south of Point Conception. However there will be the potential for
isolated dry lightning strikes as this could be an elevated
convective threat above the marine layer clouds.
*** From previous discussion ***
The deep marine layer will persist Mon night and Tue morning, with
low clouds again from the coast up to the coastal slopes along with
patchy drizzle in the L.A./VTU County vlys to coastal slopes. The
marine layer clouds are expected to clear back to the coast Tue
Onshore flow will continue Sun thru Tue, best in the afternoon and
evening hours. Some gusty S to W winds should continue each
afternoon and evening from the foothills to the mtns and deserts,
strongest Mon and Tue.
Temps will turn cooler each day Sun thru Tue, with highs about 4 to
8 deg below normal in all areas by Mon. The warmest vlys and inland
coastal areas should see highs in the 70s on Sun altho likely
reach the low 80s in the Antelope Vly. Temps will then be only in
the mid 60s to low 70s for these areas on Mon and Tue.
.LONG TERM (WED-SAT)...27/206 PM.
The EC and GFS are in pretty good agreement Wed and Thu with weak
upper level ridging over srn CA. There should be some night and
morning low clouds and fog for coastal areas during the period,
especially S of Point Conception, otherwise skies will be mostly
The forecast confidence goes down quickly for the Fri-Sat timeframe.
The EC keeps an upper level low well off the CA coast with weak
upper level ridging lingering over srn CA during the period. The
GFS, however, moves the upper level low E to near the central CA
coast by late Fri then inland thru CA Fri night into Sat, with a
cold front and a chance of showers moving into the forecast area.
For this forecast cycle have leaned more toward the EC solution with
dry weather over the region and some marine layer clouds along the
coast at least for Fri.
Temps across the region are forecast to be near normal to a few
degrees below normal for the most part thru the extended period.
Highs in the warmest vlys and inland coastal areas should be
generally in the 70s each day, except mid 70s to around 80 on Thu.
At 2320z at KLAX... the marine inversion was around 2500 feet.
The top of the inversion was around 4200 feet with a temperature
of about 19 degrees Celsius.
Overall...High confidence in the current TAFs. Late this
afternoon, low clouds continue to linger across many coastal
areas. Overnight into Sunday morning, marine layer depth will
continue to increase to around 3000 feet with low clouds and fog
expected to spread into valleys and lower coastal slopes. Also,
isolated drizzle expected, especially Los Angeles county. Another
slow clearing day expected along the coast on Sunday afternoon. An
approaching upper level low pressure system will bring a slight
chance of thunderstorms Sunday afternoon across the mountains of
Santa Barbara and Ventura counties.
KLAX...High confidence in the current TAF. MVFR low clouds will
likely continue through much of the forecast period. There is a
fifteen percent chance that CIGs will scatter between 21z and 03z.
Light southeast winds less than 8 knots are expected Sunday
KBUR...High confidence in the current TAF. IFR/MVFR low clouds
expected to return to KBUR later this evening into Sunday morning.
There is a twenty percent chance that CIGs will remain MVFR
throughout Sunday afternoon.
Winds and seas become elevated Sunday night through Tuesday but
will remain below advisory levels throughout the forecast period.
There is a slight chance of thunderstorms Sunday night through
Monday morning across the southern outer waters and across the
inner waters south of Point Conception. Any thunderstorms that
develop could produce locally gusty and erratic winds, choppy
seas, and dangerous cloud-to-ocean lightning.
.HAZARD POTENTIAL OUTLOOK (TUE-SAT).
No significant hazards expected.