Wildfire in California, July 6 to 25, 2017

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
234 PM PDT Thu Jul 6 2017

.SYNOPSIS...
Near record heat is forecast to develop Friday and Saturday as
strong upper-level high pressure centered over the Four Corners
Region slowly moves west. Mostly sunny to partly cloudy skies are
forecast, except for patchy night through morning low clouds and
fog confined to the beaches. Isolated showers and thunderstorms
cannot be ruled out for the Santa Barbara, Ventura and Los
Angeles County mountains and desert through this weekend, possibly
increasing in coverage on Sunday.

&&

.SHORT TERM...(TDY-SUN)

Infrared satellite imagery shows a ridge of high pressure over the
Four Corners Region this afternoon. Strong high pressure over the
Desert Southwest will become a staple of weather pattern for late
this week and into early next week. The ridge center will slowly
move west into Saturday and 500 mb heights and 1000-500 mb
thickness values will climb. A warming trend will continue into
Friday and Saturday with dangerously hot conditions expected away
from the beaches. Near-to-above record heat is forecast over the
next couple of days as daytime high temperatures will approach or
exceed the century mark away from the coast. Current heat
headlines seems reasonable at this time, but there is a chance
that a Heat Advisory could be added for the coastal areas south
of Point Conception.

Onshore flow will slowly weaken through the weekend as subsiding
air with the high pressure system presses down on the marine
intrusion. The marine layer depth currently around 650 feet on
KLAX AMDAR soundings will likely thin slightly more into Friday.
Patches of stratus along the Central Coast and over the Santa
Monica Bay should become less extensive and very patchy over the
next couple days. Stratus could even become non-existent,
especially Friday night and Saturday as onshore gradients weaken.
With the shallow marine layer depth, any low clouds and fog that
develop could be dense. A dense fog advisory may be needed for the
Central Coast tonight and into Friday morning where the highest
confidence exists for stratus development.

A few clouds are developing over the Los Angeles and Ventura
County Mountains this afternoon and a slight chance of showers and
thunderstorms remains in the forecast for this evening. Over the
next several days, isolated showers and thunderstorms cannot be
ruled out completely and slight chance PoPs have been left in the
forecast through Saturday. Model solutions are continuing to add a
wrinkle in the forecast over the weekend as a wave moves north
into the Region and the door opens for some monsoonal moisture to
spill into the area. PoPs and cloud cover have been bumped as
well as minimum temperatures for Saturday night into Sunday
morning. Sunday could be more clouds than sun as a cloud shield
could blanket the Region. Cloud cover could cut significantly into
temperatures on Sunday and there is a chance that temperatures
could be too warm.

Gusty Sundowner winds could develop at a few locations tonight,
but they should not be as strong as last night. KSBA-KSMX surface
pressure gradients are running weaker than this time yesterday. A
better chance exists for Friday afternoon and night and possibly
again Saturday afternoon and night as a bit better wind support
develops.

.LONG TERM...(MON-THU)

The latest model solutions indicate ridging aloft weakening early
next week and retreating to at least the Four Corners Region, and
possibly farther east into the Midwest portion of the Country. GFS
solutions suggest onshore flow strengthening as southwest flow
aloft increases ahead of a trough of low pressure progged to move
through the Pacific Northwest. A cooling trend could continue
through much of next week as the ridge retreats.

&&

.AVIATION...06/1800Z

At 1716Z at KLAX, the marine layer was around 500 feet deep. The
top of the inversion was at 3100 ft with a temperature of 29.5C.

Good confidence in the 18z TAF package. Marine clouds with IFR
conds will likely be confined to portions of the Central Coast and
possibly coastal sections of L.A. County late tonight/Fri
morning.

Gusty NW-N sundowner winds will affect the Santa Ynez Range and
the south coast of SBA County below passes and canyons this
evening through late tonight. Expect some LLWS in these areas
along with some mdt UDDF.

KLAX...Moderate confidence in the 18Z TAF. There is a 20-30%
chance of IFR to LIFR cigs between 11Z and 16Z tonight/Fri
morning.

KBUR...High confidence in the 18Z TAF with VFR conds expected
through the period.

&&

.MARINE...06/200 PM...

Across the outer waters...Small Craft Advisory (SCA) conds are
expected thru at least late Sat night. Winds may drop below SCA
levels for a few hours this morning, then again Sun morning. SCA
level winds are expected again Sun afternoon through Mon.

Across the northern inner waters...low confidence for today.
Expect winds to remain just below SCA levels this afternoon and
evening, but there is a 40% chance that winds will reach SCA
levels, and a SCA may be needed. Winds will likely reach SCA
levels Fri afternoon and evening, and possibly again over the
weekend.

Across the SBA channel, winds and seas should remain below SCA
levels thru this afternoon. There is a 30% chance of SCA conds
this evening, mainly across western portions and below passes and
canyons as gusty sundowner winds develop. SCA conds are likely
across at least western portions of the SBA channel Fri evening,
and possibly again Sat evening. Across the southern inner waters,
expect winds and seas to remain below SCA levels through Mon.

&&

.FIRE WEATHER...06/230 PM.

Northerly winds will be increasing across the Santa Barbara
County mountains and south coast this evening and peaking Friday
evening with gusts to between 40 and 50 mph possible. Humidities
between 10 and 20 percent are expected during the windiest periods
leading to several hours of critical fire weather conditions. In
addition, temperatures are expected to warm up into the 90s with
isolated locations around 100 possible, especially in the
foothills. A red flag warning is in effect for these areas
through Saturday morning. There's a chance that it may need to be
extended into Sunday morning as computer models indicate similar
if not slightly stronger winds Saturday evening.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Heat Advisory in effect until 9 AM PDT Friday for zones
      37>39-44>46-51>53-88-547. (See LAXNPWLOX).
     Excessive Heat Warning in effect from 9 AM Friday to 9 PM PDT
      Saturday for zones 37>39-44>46-51>53-88-547. (See LAXNPWLOX).
     Excessive Heat Warning in effect until 9 PM PDT Saturday for
      zones 54-59. (See LAXNPWLOX).
     Red Flag Warning in effect from 6 PM this evening to 10 AM
      PDT Saturday for zones 239-252. (See LAXRFWLOX).
PZ...Small Craft Advisory in effect until 3 AM PDT Sunday for
      zones 670-673-676. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK...(SUN-THU)
The excessive heat event will continue through at least Saturday.
Thunderstorms are possible in the mountains and high deserts
Saturday through Monday...primarily in Los Angeles County but
more widespread on Sunday.

&&

PUBLIC...Hall
AVIATION...Sweet
MARINE...Sweet
FIRE...MW
SYNOPSIS...STu/Hall

weather.gov/losangeles