Area Forecast Discussion
Issued by NWS Los Angeles, CA
FXUS66 KLOX 252345
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
445 PM PDT SUN SEP 25 2016
Gusty Santa Ana winds with hot temperatures and dry conditions
will peak Today and Monday. An upper level trough of low
pressure will help to increase the onshore flow and bring
a gradual cooling trend to the area Tuesday through the
end of the week.
Our area remains under the influence of the high pressure system
to our north which is producing offshore gradient flow to the
south and west. The LAX-DAG gradient has currently dropped to
a still-healthy -4.3 after peaking at 10am at -5.2. Advisory-
strength wind gusts are continuing in most of the forecast area.
Still expecting winds to lessen in the coastal areas by late this
afternoon, but continue into Monday afternoon in the mountains and
Santa Clarita area.
As expected, the winds have produced some very warm conditions. In
Camarillo there was a jump from 75 to 91 degrees in about 30
minutes following the wind shift to northeasterly. Currently at
102 degrees, Camarillo has tied the high temperature record for
today, but no other stations are currently in record territory.
San Fernando and San Gabriel Valleys are mostly in the mid- to
high 90s with a few hours of heating to go. Downtown LA is
currently showing 96, which is 14 degrees above normal.
Minimum temperatures in the windy areas will be well above normal
tonight but in the wind-sheltered areas the clear skies and very
dry air will allow for rapid cooling and lows will be at or below
Monday will be a little less windy (but not much) as the upper
support weakens a touch and the direction will shift to more
easterly. And the winds will shift to a bit more easterly in
direction. Monday will be the warmest day as max temps will rise
another 2 to 5 degrees.
Offshore flow will weaken Tuesday (but it will remain offshore)
The winds will diminish. There will be an earlier seabreeze and
while temps will remain much above normal they will still be
The upper low we`ve been watching to our south still looks to move
very slowly northward out of Mexico and into south central
California by Tuesday. The influence of the low will be to drop
heights and add clouds to at least the southern portion of the
area - so some definite cooling is on the horizon. There is a
non-zero chance that it could bring some mountain and desert
precipitation to the area in the afternoon as well. Will continue
to watch this low closely.
A slowly developing trof will approach from the north and then
move over California beginning on Wednesday. Marine layer stratus
should return to at least the central coast.
GFS and EC both agree that a slowly developing trof will approach
and then move over the state from Wednesday to Saturday. The
offshore flow will turn onshore on Thursday. There will be cooling
trend through the period with Max temps reaching near normals on
Friday and then blo normal on Saturday. The marine layer stratus
will struggle to reform Wed and Thu and will affect just the
central coast. The increased onshore flow and deeper marine layer
will help establish a coastal marine cloud pattern on Friday and
then a coastal/valley pattern on Saturday.
At 2330Z...there was no marine layer at KLAX. The inversion was
surface base with a top of 1700 feet and a temperature of 30 degrees
Overall, high confidence in 00Z TAF package as offshore flow will
keep all sites VFR. There will be the potential for some LLWS at
KLAX, KLGB, KBUR, KVNY, AND KOXR tonight through early Monday
morning as offshore winds increase once again above the surface.
KLAX...high confidence in 00Z TAF with VFR conditions through the
period. Moderate confidence in easterly winds 5 to 7 knots
overnight into Monday morning. There is also the potential for
LLWS during this period.
KBUR...high confidence in 00Z TAF with VFR conditions through the
period. There is also the potential for LLWS overnight.
There is a slight chance northeast winds will create small craft
advisory conditions near shore in an area from Ventura Harbor to
Pacific Palisades Monday morning. Otherwise small craft advisory
conditions are not expected Tuesday through Thursday. Northwest
winds are expected to increase from Piedras Blancas to Point Sal
10-60nm and from Point Sal to San Nicolas Island and create small
advisory conditions Friday.
An extended period of critical Red Flag fire weather conditions
across much of Los Angeles and Ventura counties through Monday,
with elevated fire danger across remaining areas. As of 4 pm, the
sea breeze has returned to the coastal plain with gusty offshore
winds continuing across the interior. Another burst of offshore
winds are expected to occur across the typical wind prone areas
of LA/Ventura counties tonight into Monday morning. The LAX-
Daggett gradient is expected to peak around -5 mb again on Monday
morning. The upper level support looks favorable for tonight, then
weakens slightly by Monday morning and becomes more easterly
in nature. Also of note, will be the very warm overnight lows
with some foothill and windy locations remaining above 80 degrees.
These same areas will see poor humidity recoveries only in the
teens. Continued very hot and dry conditions on Monday will
likely maintain the critical fire weather conditions. Very rapid
fire spread and extreme fire behavior...including long range
spotting...is likely for any new fire ignitions due to these
critical fire weather conditions and the exceptionally dry fuels.
By Tuesday there is a 10 to 15 percent chance of thunderstorms
across Los Angeles and Ventura counties in response to mid level
moisture possibly working its way into the area from the
southeast. Otherwise, gradual cooling is expected to continue
through the middle to end of next week with a slow increase in
marine layer coverage to the west of the mountains.
CA...Wind Advisory in effect until 6 PM PDT this evening For zones
40-41. (See LAXNPWLOX).
Wind Advisory in effect until 3 PM PDT Monday For zones
44>46-53-54-547. (See LAXNPWLOX).
Red Flag Warning in effect until 3 PM PDT Monday For zones
240-241-244>246-253-254. (See LAXRFWLOX).