Area Forecast Discussion
Issued by NWS Los Angeles, CA
FXUS66 KLOX 261014
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
314 AM PDT MON SEP 26 2016
Upper level high pressure will continue to bring gusty Santa Ana winds
with hot temperatures and dry conditions to the area today. 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.
Its all about the winds and temps today. DAG gradient is still
trending offshore and is now at -4. There is an onshore trend to
the north. This will make the winds a little more easterly than
they were yesterday. The upper support is weaker so the winds will
be weaker and shorter lived that ydy as well. Still there will be
advisory level gusts through the mountains and the vlys of LA and
VTA counties near the county line...as well as the Ventura county
coast. Due to warmer air mass max temps are going to equal or
exceed yesterdays very warm numbers. Areas near the beaches esp
along the central coast will see their daily highs set in the late
morning followed by steady cooling during the afternoon.
Tuesday will remain warm. There will be some east winds in the
morning but with much weaker sfc grads and upper support there
will be no advisory level gusts. There will be decent cooling
across the coastal sections but less inland. An additional concern
for Tuesday will come from an upper low moving in from Mexico it
will bring partly cloudy skies to VTA and LA counties which will
help to knock a few degrees off of max temps there as well. There
is a non zero chc of a mtn shower or tstm but still too low to
mention in the forecast. The better shower activity will occur to
the south and east of LA county.
On Wednesday morning there will be some marine layer stratus over
the Central Coast. The upper low to the east will still be
spinning clouds over the area and creating partly cloudy skies.
The low will be in a better position to advect some moisture and
mid level dynamics into the area. Enough moisture and dynamics to
warrant a slight chc of TSTMs over the LA and VTA mtns in the
afternoon and early evening. Max temps will continue to fall but
they will still be above normal.
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 moderate chance northeast winds will create small
craft advisory conditions near shore in an area from Ventura
Harbor to Pacific Palisades Monday morning to early Monday
afternoon. Otherwise...small craft advisory conditions are not
expected over the coastal waters 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 8 pm, the
sea breeze continues across 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. There is a 20 percent chance of thunderstorms by
Wednesday afternoon across the mountains of LA/Ventura counties
and Antelope Valley. If any storms were to develop on Tuesday or
Wednesday, there would be some concern over potential dry
lightning strikes due to a fairly dry lower atmosphere.
CA...Wind Advisory in effect until 3 PM PDT this afternoon For
zones 40-44>46-53-54-547. (See LAXNPWLOX).
Red Flag Warning in effect until 3 PM PDT this afternoon For
zones 240-241-244>246-253-254. (See LAXRFWLOX).
PZ...Small Craft Advisory in effect until 3 PM PDT this afternoon
For zone 650. (See LAXMWWLOX).