Scientific Forecaster Discussion
Southwest California area forecast discussion
National Weather Service Los Angeles/Oxnard California
1026 am PDT Wednesday Mar 12 2014
high pressure in the Great Basin will result in gusty offshore winds
for parts of the area today...along with warm and very dry
conditions. Weaker offshore flow will continue for the remainder of
the week...bringing more warm and dry weather. High pressure
building aloft and an increase in offshore flow over the weekend
will result in further warming. Cooler weather is possible by the
middle of next week as low pressure approaches.
Short term (today-fri)...
middle-morning discussion update...
strong and gusty winds are blowing across the service area this
morning and are expected to increase a bit more through midday.
Current forecast package has this as a one day event and this luks
to be on track. Weaker winds could redevelop tomorrow morning in
the predominant Ventura and Los Angeles County northeast wind areas
but at this time these luk to remain below advisory levels.
Another question for tomorrow morning will be whether the marine
layer redevelops... along the Los Angeles County coast in
particular... and to what effect regards ceilings and visibility.
This would be counter intuitive to having strong offshore winds but
it came in to a moderate extent this morning and guidance suggests
another reformation tomorrow so will be lukg further into that as
Longer term issues are the extent of high temperatures this weekend
and the suggestion of some precipitation next week. Will probably
not make any notable moves on the latter but may tweak temperatures
a bit for this weekend. Bottom line will be relatively hot temperatures
for a March weekend.
Early morning discussion...
wind event...as it so often happens...has been slow to start. But
winds are picking up and by dawn the event should be well under way.
NAM has finally come into line with the GFS/ec and the upper low has
settled in about 100 miles north of klas. So this wind event will
not get the best upper level support. 1032mb surface high over NE Nevada has
created a -4 mb gradient from kdag. There will be lots of cold air
advection however as the upper low spins in much cooler air from the
interior. Heights will fall about 10 dm over interior today and and
about 5 dm towards the coast. The cold air and the surface gradients
will combine to produce a decent but not spectacular wind event and
look for low end warning gusts to 60 miles per hour in the mountains and high end
advisory gusts to 50 miles per hour in the valleys (xcp san gabriel) of la and vta
County. The vta coast as well as the Malibu strip will also see
advisory level gusts and some area in the Ventura County coast may
see 30 miles per hour sustained winds. It will also be breezy across much of
sba and slo County and 20 to 30 miles per hour gusts will be common this
One would think that with such a panoply of wind products out there
would be no marine layer but thats not the case. A weak eddy formed
last evening and coupled with the late to arrive winds some stratus
developed in the lgb area as well as the San Gabriel valley. Satellite
shows these clouds dissipating as the winds finally pick up and by
dawn skies should be mostly clear.
Temperatures today will be tricky as the cold air advection will cool the
interior but the NE flow will allow for adiabatic compression and
warming. The beaches will likely be among the warmest place today
with maximum temperatures in the 80s. The central coast will have pockets of
warm maximum temperatures where ever the east winds set up.
The surface gradient will relax late this afternoon as the surface high
pulls out to the east and the cold air advection will end. This will
quickly end the winds.
Thursday and Friday now look tricky as new NAM shows weak eddy each
morning and good humidities over the beaches. So it looks like there
may well be low clouds each morning. The weaker offshore flow will
not allow as much warming and the coasts and valleys will cool but the
lack of cold air advection will allow maximum temperatures to rise over the
mountains and the interior.
Low temperatures away from the coast will cool to below (and well below
normal interior vlys) due to the dry air and clear skies.
Long term (sat-tue)...
cool is not a word that will be associated with this weekend. As a
ridges pushes into the state from the SW. Heights rise to 580 dm
Saturday and 585 dm Sunday. These heights are about 15 dm higher than
average and combined with offshore flow at the surface maximum temperatures will
skyrocket into the upper 80s and lower 90s across the valleys. A few
records will likely fall over the weekend especially sun. The models have
been trending a little stronger with the offshore event on Saturday
and one could make a case that some low grade advisories may be
GFS disagree on the forecast for early next week. GFS knocks the
ridge down with an approaching upper low while the ec slowly moves
the ridge to the southeast. Either way there will be some cooling more so
with the GFS but maximum temperatures will still be above normal.
Ridge (ec) upper low (gfs) for Tuesday. Forecast calls for cooling not
as much as GFS would bring...but this could easily be wrong.
Middle/upper level low centered over the central San Joaquin Valley
will shift southeast. Upper level moderate to strong west southwest
winds will become moderate north and middle level light south southwest
winds will become moderate north by 13/14z over the area. Mixed weak
onshore and weak offshore pressure gradient through 13/04z and weak
offshore gradient between 13/04-13/17z then weak to moderate onshore
gradient through the remainder of the period. Marine clouds were
pushed offshore and an isolated cloud field may return late in the
evening and will be pushed south of the area Thursday morning.
Klax...low chance ceilings 017 at times between 13/06-13/10z. Otherwise
chance between 010-020 winds 07014kt through 12/20z.
Kbur...chance between 018-020 winds 04030kt through 12/22z.
Otherwise current sky/visibility conditions very likely through period.
Virtually certain - 95-100%
very likely - 80-95%
likely - 60-80%
chance - 30-60%
very unlikely - 20% or less
Moderate to strong offshore winds will form by Wednesday over Los
Angeles and Ventura counties...as well as interior Santa Barbara and
San Luis Obispo counties. Elevated fire concerns will exist today.
As the winds increase tonight into Wednesday...cold air from the low
will bring increased humidities...especially in the
mountains...which will take time to lower through the day on
Wednesday...first near the coast early Wednesday morning...then up
through the higher elevations in the afternoon. Despite the higher
humidities...sustained winds around 40 miles per hour and gusts around 65 miles per hour
are likely during the peak on Wednesday over Los Angeles and Ventura
counties...which would create an environment favorable for extreme
fire behavior if a fire starts. These winds will push into interior
San Luis Obispo and Santa Barbara counties as well. A red flag
warning will be issued for Los Angeles and Ventura counties as well
as the interior portions.
Weaker but still gusty northeast winds will continue Wednesday night
through Thursday...with elevated fire concerns.
High Wind Warning (see laxnpwlox).
Red flag warning (see laxrfwlox).
Wind Advisory (see laxnpwlox).
Small Craft Advisory (see laxmwwlox).
Marine weather statement (see laxmwslox).