Scientific Forecaster Discussion
Southwest California area forecast discussion...updated
National Weather Service Los Angeles/Oxnard California
515 PM PDT Wednesday Oct 1 2014
Updated aviation section
A significant warming trend is expected into the weekend as surface
high pressure builds into the Great Basin and offshore flow
strengthens through late this week. Weaker offshore flow is expected
for the weekend...but hot and dry weather will continue as high
pressure builds aloft. Cooler weather is possible early to middle next
Short term (today-sat)...interior areas and central coast seeing
the initial shot of Santa Ana winds today, pretty much right on
schedule. Winds will do their usual diurnal shift and weaken during
the afternoon and evening before returning with the main offshore
push overnight and early Thursday which will bring winds down to coast
and valley areas (except la coast). Because it's primarily gradient
driven it's still looking like a low grade Santa Ana wind event at
best with some isolated gusts in the middle 40s in the favored (and
generally unpopulated) areas while most areas see sub-advisory level
winds in the 30s or less. On Friday winds are expected to be about
10 miles per hour less than Thursday but still breezy in the usual spots.
Temperatures expected to jump several degrees Thursday with highs in the
80s and 90s, then another 3-6 degrees Friday. Coastal areas will
probably see biggest warmup Thursday while on Friday the bigger jump will
be the interior as cold air from the passing trough exits the area.
Sat still expected to be the warmest day. Offshore winds should be
fairly light as gradients weaken.
Highs through Saturday will threaten daily records but most
locations will probably fall just a little short. Santa Maria's
record of 96 Thursday may be the exception. Heat index levels are not
expected to reach our warning threshold of 105 because widespread
humidities under 10% results in heat index values about 5-7 degrees
below the ambient air temperature.
Long term (sun-wed)...cooling trend to begin Sunday as gradients
start turning onshore. However, it will still be several degrees
above normal. Normal temperatures expected to return by around Wednesday.
Skies expected to remain clear, except for some coastal marine layer
clouds returning Monday or Tuesday.
VFR conditions are expected throughout the period...except for a
slight chance of vlifr to LIFR conditions at coastal terminals south
of Point Conception between 10z and 16z. Periods of wind shear are
possible at koxr mainly between 08z and 18z...with a chance of wind
shear at Los Angeles County valley terminals.
Klax...VFR conditions are expected throughout the period. There is a
20 percent chance of vlifr to LIFR conditions mainly between 10z and
Kbur...VFR conditions are expected throughout the period. There is a
30 percent chance of low-level wind shear and turbulence mainly
between 08z and 18z.
For the outer waters...for tonight and through the weekend...winds
are expected to remain below Small Craft Advisory levels.
For the inner waters...high confidence in winds remaining below
advisory levels through this evening. By late tonight and Thursday
high confidence in northeast winds developing with a chance of winds
reaching Small Craft Advisory thresholds Thursday morning
(especially near shore) from Ventura to Malibu and out to the
islands. For Friday through the weekend...weak offshore flow can be
expected at night...and weak onshore flow in the afternoon/evening
A long period south-southwest swell is anticipated to arrive on
Wednesday and continue through Friday.
Fire weather...01/1220 PM.
Gusty northeast winds will start to form today over interior Los
Angeles County...which could produce a few hours of critical
conditions over the Santa Clarita valley as humidities start to
drop. These winds will strengthen and push down into the valley and
coastal sections tonight through Thursday. Meanwhile...a ridge of
high pressure will build over California and bring hot and very dry
conditions to the region...with humidities around 10 percent over
most areas by Thursday afternoon. As a result...widespread critical
conditions are likely over much of Los Angeles and Ventura counties
on Thursday. Mountain and valley areas have the best chance to
exceed the 6 hour duration thresholds...but some coastal areas
should see a few hours of critical conditions as well. San Luis
Obispo and Santa Barbara counties will have elevated fire concerns
as well with hot and very dry conditions...but winds will be weaker
and very localized...mostly confined to select Interior Valley and
Conditions will become hotter and drier Thursday night through
Saturday...but the winds will weaken each day. There is a chance
that red flag conditions will continue Thursday night through
Friday...but less certain than Thursday due to the weaker winds.
Regardless...triple digit temperatures and widespread single digit
humidities will maintain a period of elevated fire concern. Cooling
and moistening expected gradually next week.
red flag warning (see laxrfwlox).
Fire Weather Watch (see laxrfwlox).
Special Weather Statement (see laxspslox).