Scientific Forecaster Discussion
Southwest California area forecast discussion
National Weather Service Los Angeles/Oxnard California
350 am PDT Tuesday Mar 11 2014
..updated aviation discussion...
Offshore flow will bring gusty and possibly damaging winds to the
area today and Wednesday. High pressure will keep afternoon
temperatures above normal through the period with a very warm
weekend on tap.
Short term (today-thu)...
northwest flow over the area as a ridge builds into the west and trough moves
through Nevada. The gradient from kbfl is at -6mb thanks to strong
surface pressure over Oregon the kdag gradient is neutral now but is
quickly turning offshore as well. The north flow is pushing some
clouds up against the mountains and into the Cuyama Valley so look for a
cloudy start to the day there. A weak eddy will bring just a few low
clouds to the lgb area. Partly cloudy elsewhere as high level clouds
drift overhead. Wind advisories are in place for most of l.A. And
vta counties (esp the I-5 corridor...the Santa Clarita valley and the
20 mile area along the la/vta County line. Advisory level gusts will
likely develop after sunrise and continue into the early afternoon.
The offshore flow will keep maximum temperatures above normal across the coasts
and valleys. Trickiest temperature forecast is over the central coast where 15 to
25 miles per hour NE winds are occurring now. If these winds last into late
morning there will be many highs in the lower 80s if the winds
subside middle morning maximum temperatures will only reach the middle 70s at best.
These temperatures will likely fall through the afternoon as a sea breeze
moves over the area.
Main forecast focus is on potential High Wind Warning event late tonight
and Wednesday. Unfortunately there is no change in the forecast. NAM
continues to bring an upper low to the Las Vegas area which in turn
provided lots of upper and thermal support to the strong offshore
surface gradient. The ec and GFS keep the upper low further to the
north and forecast little upper support and even less thermal support.
So the NAM indicates a Middle Range High Wind Warning event and the GFS
and ec forecast a MDT to strong Wind Advisory. Will extend the Baton to the
day shift for the ultimate decision on whether to issue a warning
or advisory and hope the 12z guidance agrees better. What ever the
winds they will die off pretty quickly in the afternoon as the surface
pressure diminishes along with any upper support. Offshore flow
will keep well above normal temperatures going across the csts and valleys
while the interior will cool a little as cooler air filters in from
Nice day Thursday. Weak offshore flow will make for some 15 to 25
miles per hour canyon breezes. Sunny skies and rising heights will allow for a few
degrees warming everywhere...except perhaps the central coast which
should have little no east morning winds and an earlier sea breeze.
Long term (fri-mon)...
all models agree that Friday through Sunday will be dominated by high
pressure and weak offshore flow. Look for clear skies and well above
normal maximum temperatures (not record breaking) Sunday will be the
Models disagree on Monday forecast with some models keeping the ridge and
others flattening it with a Pacific northwest trough. Trended forecast cooler but
not as much as the coolest solution would suggest.
Overall...high confidence in 12z taf package. VFR conds expected for
all sites through the period. Main issue will be developing north to
northeast winds. Winds will increase this morning...then exhibit a
lull this afternoon/evening...then become stronger tonight/Wednesday
morning. So...will expect north to northeast winds in the usual
spots today (koxr/kvny/kpmd/kwjf). For tonight/Wednesday
morning...with the offshore winds expected to be stronger...will
introduce some low level wind shear in the valley taf sites.
Klax...high confidence in the 12z taf package. There is a 10% chance
of MVFR/IFR ceilings between 12z and 16z. Late tonight...low level wind shear and
turbulence could be issues as offshore winds increase across the la
Kbur...high confidence in 12z taf. Low level wind shear/turbulence will be main
concerns tonight/Wednesday morning.
Gusty offshore flow is expected Tuesday through Thursday...peaking
on Wednesday and focusing over Los Angeles and Ventura counties. Dry
air from the offshore flow this last weekend will linger through
Tuesday with minimum humidities mainly under 15 percent...which will
result in a number of hours of red flag conditions over much of the
wind prone areas of Los Angeles and Ventura County on Tuesday as the
As the winds increase further Tuesday night 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 Wednesday morning...then up through
the higher elevations in the afternoon. Despite the slightly higher
humidities...there is a potential for sustained winds above 40 miles per hour
and gusts above 60 miles per hour during the peak on Wednesday...which will
bring a potential for extreme fire behavior if a fire started. A
Fire Weather Watch will be in effect as a result.
Gusty northeast winds will continue Wednesday night through
Thursday...but will be significantly weaker on Wednesday. Humidities
however will lower some...and if Wednesday proves to be red flag
worthy...this period may need to be added as well.
high wind watch (see laxnpwlox).
Fire Weather Watch (see laxrfwlox).
Wind Advisory (see laxnpwlox).