Scientific Forecaster Discussion
Southwest California area forecast discussion
National Weather Service Los Angeles/Oxnard California
342 am PST Tuesday Dec 10 2013
strong and gusty Santa Ana winds across Los Angeles and Ventura
counties will diminish by afternoon...then locally gusty winds will
continue at times through Thursday morning. Daytime temperatures
will remain well below normal today...then will rise to near normal
levels by middle week...and to above normal levels over the weekend and
early next week. The nights will be cold in many areas through
Thursday night with patchy of frost in wind sheltered locations.
Dry weather is expected through the weekend.
Short term (today-thu)...gusty winds continued to affect much of Los
Angeles and Ventura counties this morning. Upper support was
beginning to weaken as the best subsidence and strongest winds aloft
shift eastward away from the area. However...pressure gradients are over
7 mb offshore between klax and kdag...stronger than at this time on
Monday. Will let high wind warnings expire at 4 am for the mountains of l.A.
And vtu counties and the Santa Clarita valley since only isolated
warning level gusts are expected this morning. Overall though...
expect winds to remain at rather high end Wind Advisory levels
through the morning in these areas...and wind advisories will be in
effect through noon.
Wind advisories also are in effect until noon for coastal and valley
sections of vtu County...the San Fernando Valley (especially northern and
western sections) and the Los Angeles County coast below passes and
canyons from Malibu to the Hollywood Hills. Winds should drop off to
below advisory levels in most areas by noon.
Hard freezes were occurring again this morning on the central
coast...in the Santa Ynez Valley...on the South Coast of sba County
and in wind sheltered interior valleys of vtu County such as the
Ojai Valley. Temperatures should rise above freezing in most areas by middle
Skies were mostly clear across the region...with the exception of
southern sections of l.A. And vtu counties...where a high cloud shield
from a weak upper level system to the SW of the region has pushed
into that area. Will go with a partly cloudy forecast for coastal
and valley areas of l.A. And vtu counties...although clouds may thin
during the day. Maximum temperatures should be up a few degrees from those
reported on Monday...but should still be well below normal...except
just a few degrees below normal across the coastal plain.
A positively tilted upper ridge will nose into northern California and the Pacific northwest
tonight and Wednesday then persist through Thursday. A weak upper low well to
the SW of the region will move little through Wednesday...then drift eastward
into northern Baja California and extreme Southern California on Thursday. Low level gradients will
remain moderately offshore through the period. Expect areas of gusty
NE winds in the mountains and most valley locations of l.A. And vtu
counties and the vtu County coastal plain during the late night
through morning hours tonight through Thursday. Winds should stay below
advisory levels in most areas. Interestingly...the 06z runs of
both the WRF and the GFS actually show an increase in wind Thursday
morning...likely due to some increase in upper support and NE
flow aloft as the upper low tracks just S of the region. Maximum temperatures
will rise to near normal levels in most areas on Wednesday...with warmest
locations reaching about 70 degrees...then little change in maximum
temperatures expected on Thursday.
It will be cold again tonight...but not as cold as the past few
nights. Still...frost advisories may be needed for the central
coast...the Santa Ynez Valley...the S coast of sba County and the
interior valleys of vtu County. Wednesday night should be a few degrees less
cold. Skies should be mostly clear Wednesday through Thursday...with the
exception of a few high clouds from time to time.
Long term (fri-mon)...the upper low over northern Baja California and extreme Southern
California will shift eastward Thursday night and Friday and a weak trough moving through
the Pacific northwest will flatten as it drops into the Great Basin. This will
leave a broad northwest flow pattern aloft across the region...with just
some high clouds on Friday. Although heights rise a bit...offshore flow
will weaken or turn onshore...offsetting any warming...at least west
of the mountains an upper ridge will amplify along the West Coast on Sat
and low level flow will turn offshore...bringing some warming to the
region...with additional warming Sunday and Monday as heights continue
to rise and offshore flow persists. Expect temperatures to rise to slightly
above normal levels on Sat...then possibly to well above normal
levels Sunday and Monday...with highs possibly reaching or exceeding
80 degrees in some coastal and valley areas.
Overall...high confidence in 12z taf package. Offshore flow will
keep all taf sites VFR through the period. There will be another
round of gusty northeast winds this morning with the usual low level wind shear and
Klax...high confidence in 12z taf.
Kbur...moderate confidence in 12z taf. There is a 40% chance that
northerly winds could surface for a few hours this morning.
Fire weather...elevated fire danger will continue today due to the
gusty offshore winds and very low humidity. Through and below
favored passes and canyons in the mountains and valleys of l.A. And vtu
counties and across the vtu County coastal plain...NE winds of 20 to
30 miles per hour with gusts of 40 to 50 miles per hour will continue this morning.
Relative humidities have only "recovered" to between 12 and 18
percent in most areas of l.A. And vtu counties overnight...and a few
locations still had single digit humidities early this morning.
Critical fire weather conditions may be reached in a few locations
for several hours this morning.
The offshore winds are expected to gradually diminish late this
morning through this afternoon. However...there will be several
hours of single digit humidities and some warming that will help to
further dry the fine dead fuels.
gusty northeast winds will affect the inner waters through middle
morning. The strongest winds will be over the waters from Ventura
and southward to Santa Monica...extending westward to anacapa and
Santa Cruz islands. East to northeast winds with gusts to 25 to 30
knots are expected in this area as well as over the San Pedro
Channel out to Catalina Island.
Small craft advisories remain in effect for the gusty winds and for
the choppy short period seas that will result from the winds.
Easterly winds waves of 3 to 5 feet are expected over the waters and
may also affect Avalon Harbor and Smugglers Cove at times through
early Tuesday. Hazardous conditions may be expected for boaters in
east facing harbors...and for improperly moored vessels exposed to
freeze warning (see laxnpwlox).
Wind Advisory (see laxnpwlox).
Small Craft Advisory (see laxmwwlox).