Scientific Forecaster Discussion
Southwest California area forecast discussion
National Weather Service Los Angeles/Oxnard California
1040 am PDT Monday Mar 30 2015
Updated aviation and marine sections
Cooler weather is expected early this week due to onshore flow.
Night through morning low clouds and fog will be possible along
parts of the coast. Gusty northwest to north winds will develop for
parts of the area on Tuesday and Wednesday as several moisture
starved fronts pass to the North. Well above normal temperatures are
expected late in the week as Santa Ana conditions develop.
Short term (today-wed)...a bit of a cooling trend today through the
middle of the week. Local profilers and soundings indicate 3-6
degrees of cooling below 2000' which is near the top of the marine
layer this morning. The forecast looks on track through the weekend
and not expecting much change from what has already been discussed.
***From previous discussion***
A trough approaches the area Tuesday and onshore flow to the east
really increases. This should allow a better Marne layer cloud
pattern to form with clouds over most of the coast and much of the
valleys. There will be decent west winds in the mountains and deserts. Maximum
temperatures will fall across the board but will still be above normal.
Strong north gradients set up Tuesday night and there will be
another round of sundowners and I-5 corridor winds. The valleys will
also see some north winds. Some low end advisories may be needed for
the overnight and Wednesday morning hours. The north push will
eliminate the marine layer stratus everywhere except the southern la
coast. There will be some cold air advection which will serve to
cool things off...especially inland but there will also be some
compressional heating which will negate or even overwhelm some of
the cold air. Over all temperatures will be a mixed bag. The biggest change
will be inland away from the downslope flow where it will be cooler.
Long term (thu-sun)...
Thursday will be much like Wednesday with a good north push and possible
low end wind advisories across the I-5 corridor and the sba South
Coast. The cool air will be gone and this will allow for slightly
warmer temperatures than on Wednesday. The marine stratus again will be
confined to the la South Coast and that forecast may be on the
pessimistic side. There will be some North Slope clouds due to the
strong north to south flow out of the Central Valley.
Quick hitting ridge and Santa Ana wind event is slated for Friday. A
1034 mb surface high moves into Nevada Friday morning and will generate
gusty near advisory level NE winds across la and vta County. Maximum
temperatures will soar into the middle and upper 80s across much of the CST
and valleys. Skies will be sunny with nary a trace of marine layer
Still offshore for Saturday but the ridge aloft will be replaced by
a trough so this will knock a few degrees off of the temperatures as will an
earlier sea breeze since the offshore flow will relax earlier in the
day as the troughs influence begins to assert itself. Still no low
clouds although skies may be partly cloudy as the result of some middle
level clouds associated with the trough.
A quick and strong switch to onshore flow Sat night along with
trofing aloft will also a deep and penetrating marine stratus
layer to form and move across the coasts and into the valleys. Could be
some slow clearing Sunday and maximum temperatures will collapse.
At 18z at klax... the inversion was 1584 feet deep with the top at
2484 feet and a temperature of 20 degrees celsius.
Overall... moderate confidence in the 18z tafs from ksba southward
to klgb. Higher confidence for northern taf sites. Marine layer is
shrinking along the Ventura and Los Angeles County coasts but may
hold most of the day along the central coast with local MVFR
ceilings near the beaches. Expect a slightly stronger offshore
flow along the central coast tonight with less overall low cloud
coverage. Catalina eddy will bring MVFR/IFR ceilings and visibilities to the
Ventura and Los Angeles County coasts shortly after 04-05z.
Klax... moderate confidence in the 18z taf. VFR conditions through
02z with IFR ceilings after 05-06z. Visibilities lowering to IFR by 09z. Marine
clouds will break up after 16z Tuesday.
Kbur... high confidence in the 18z taf. No significant change to
current VFR conditions.
Small craft advisories are in effect for the central and southern
outer waters through late tonight. The winds will likely increase
overnight and a gale watch will likely need to be converted to a
Gale Warning for Tuesday through Thursday night for the entire outer
waters and the nearshore zone along the central coast. The strongest
winds look to be Wednesday afternoon into Wednesday night.
A fresh west-northwest swell will mix in with locally generated seas
through Wednesday and steep combined seas above 10 feet will likely
persist near shore through Friday. Patchy dense fog with
visibilities less than one nm are expected in the overnight periods
for the next couple of nights.
Beaches...a long period swell from then southern hemisphere will
continue through this evening. Expect elevated surf and strong rip
currents and longshore currents along exposed south facing shores.
***warmest March on record in many locations***
With just two days left in the month...confidence is high that March
2015 will be the warmest March since weather records began at most
locations in southwestern California. This includes downtown Los
Angeles...where records began in July 1877...and records for March
began in 1878. Out of a total of 138 marches (including this
one)...March 2015 is running about 2 degrees warmer than the next
warmest March...March 1931. Breaking a monthly average temperature
record by about 2 degrees is very unusual...especially one with a
period of record all the way back to 1878.