Area Forecast Discussion
Issued by NWS Los Angeles, CA-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
FXUS66 KLOX 250540
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
1030 PM PDT SAT SEP 24 2016
Gusty Santa Ana winds with hot and dry temperatures will peak Sunday
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.
A 597 dm area of high pressure that is currently 700 miles west of
Los Angeles is continuing its slow march toward California.
Meanwhile high pressure over the surface of Idaho is building and
sliding south...still on track to arrive in the Utah/Nevada area
tomorrow. The hot and windy weather story we have been advertising
for Sunday and Monday remains on target. Winds are mostly
behaving themselves at this point with a few spots gusting to
around 20 mph. These winds should start picking up after midnight
tonight over Los Angeles and Ventura Counties...first for the
mountains...then into the valleys early Sunday morning...then into
the coastal sections by around 9 am. Peak gusts between 35 and 55
mph are still the target...and the current wind advisories look
good (though the start time is on the early side).
Temperatures will be on the rise on the coastal side of the
mountains, and while the current forecast may be a bit on the hot
side, the general idea is hard to argue with. High temperatures
between 92 and 102 will be common, but records are quite high and
look safe. Regardless, heat-related illnesses will be a serious
concern and sensitive populations (like outdoor workers, the
elderly, and children) should get prepared now. Fire weather
concerns abound to no surprise and the current suite of Red Flag
Warnings look good.
Looking further out, computer projections are looking more
favorable for convection on Tuesday as a low currently forming
over Arizona wobbles up into southern California. If the current
solutions hold, we will probably need to mention thunderstorms in
the forecast for at least the Los Angeles and Ventura County
mountains and deserts.
Latest guidance was reasonably consistent with previous runs
through the period and dry conditions will persist with a cooling
trend. Temperatures near the coast will likely be 5-10 degrees
below normal within a marine layer while above normal
temperatures persist in the interior under clear skies but the
interior areas are expected to trend cooler by 2-4 degrees each
day through the period. Otherwise the remnant tropical low
centered east of the area will shift east as a mid latitude trough
advances over the Eastern Pacific Wednesday. The mid latitude
trough is expected to amplify while approaching and
height/thickness will lower/decrease over the area through the
At 0500Z at KLAX, there was no marine layer. There was a sfc based
inversion with a top of 1600 feet and temperature of 28 degrees C.
Very high confidence in CAVU TAFs. There will be some LLWS at all
terminals through 18Z.
KLAX...Very high confidence in CAVU TAF. There is a 40 percent chc
that the east winds will not be as strong as fcst.
KBUR...Very high confidence in CAVU TAF.
Easterly winds will flirt with Small Craft Advisory (SCA)
thresholds from Ventura to Malibu Sunday and Monday from 8am to
2pm. 40 percent chance of east winds pushing out through the
Channel Islands to Point Conception. 20 percent chance of the
east winds reaching Avalon. Despite these east winds...stiff
westerly breezes are likely near the coast each afternoon. There
is a chance for 10 to 20 knot southeast winds Tuesday morning from
Point Conception to San Onofre including the San Pedro and Santa
Barbara Channels. Dense fog will be possible after Tuesday off the
Central Coast and after Wednesday elsewhere.
.FIRE WEATHER...24/500 PM.
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. Widespread minimum
relative humidities so far today have been between 8 and 15
percent away from the coast. North to northeast winds are currently
gusting 20 to 35 mph across the Los Angeles and Ventura County
Mountains and Valleys with similar winds expected through this
evening. The Santa Ana winds are then expected to increase in
areal coverage and intensity late tonight and especially Sunday,
when the offshore winds are expected to spread all the way to the
coast from Ventura to Malibu with peak gusts ranging up to 55 mph
across the mountains and up to 45 mph closer to the coast. LAX-
Daggett gradient expected to peak around -5 mb on Sunday morning,
along with better upper level wind support. The most critical fire
weather conditions are expected on Sunday across Southern
California due to the stronger Santa Ana winds, widespread triple
digit temperatures, and widespread single digit humidities. This
type of critical fire weather scenario combined with the
exceptionally dry fuels would bring the potential for very rapid
fire spread along with extreme fire behavior (including long range
spotting) for any new fire ignitions. In addition, very warm
temperatures and poor humidities can be expected at night across
the foothills and wind prone areas. Gusty Santa Ana winds will
likely continue Sunday night into Monday but wind gusts are not
expected to be quite as strong and will be more easterly in
nature. Continued very hot and dry conditions on Monday will
likely maintain the critical fire weather conditions.
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 from 6 AM to 6 PM PDT Sunday For
zones 40-41. (See LAXNPWLOX).
Wind Advisory in effect from midnight tonight to 3 PM PDT
Monday For zones 44>46-53-54-547. (See LAXNPWLOX).
Red Flag Warning in effect from midnight tonight to 3 PM PDT
Monday For zones 240-241. (See LAXRFWLOX).
Red Flag Warning in effect until 3 PM PDT Monday For zones
244>246-253-254. (See LAXRFWLOX).