Area Forecast Discussion
Issued by NWS Los Angeles, CA
FXUS66 KLOX 281838
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
1138 AM PDT SUN AUG 28 2016
High pressure building aloft will bring a warming trend through
early this week, along with decreasing marine layer cloud
coverage. Triple digit heat is expected in some valley areas on
Monday and Tuesday. Cooler conditions and an increase in night
through morning low clouds and fog are expected for the second
half of next week as a broad trough of low pressure develops.
Temps racing off to a much faster start in many areas thanks to
1-2mb offshore trends, a stronger ridge aloft, and a shrinking
marine lyr. Forecast today calls for 5-10 degrees of warming on
average with the biggest up trends in the coastal valleys and
mountains. Increasing north flow tonight will generate locally
gusty sundowner winds through the Santa Ynez range passes and
canyons, especially the western portion. Not really widespread
enough for advisories tonight, but better coverage and stronger
Monday and Tuesday nights along with drier conditions that may
require a fire weather watch in that area. Low clouds tonight
likely confined to the Central Coast and LA County coast.
***From previous discussion***
The ridge axis will move overhead Monday and the offshore trends
will continue. Look for 4 to 8 degrees of warming across the area.
The coasts will remain blo normal altho only by a degree or two
while the vly max temps will rise up to 8 to 12 degrees above
There will be even less low clouds Monday night and most areas
will likely just have clear skies.
A trof will begin to move into the state on Tuesday. It will allow
for some cooling across SLO and SBA counties but VTA and LA
counties due to the offshore trends and limited overnight cooling
will likely warm another degree compared to Monday.
The EC and GFS agree on the Day 4 to 7 forecast. A broad upper
level trof will set up off the CA coast. There will be dry sw
flow aloft over CA. Hgts will fall to 585 DM which will cool the
interior to normal by Friday or Saturday. The Marine layer will
increase and push into the vlys and by Friday it should be all the
way into the Santa Clarita Vly. This will cause the biggest drop
in max temps. Closer to the coast max temps will remain blo normal
and the cooling trend will be much more subtle. It looks like its
going to be an August without a Monsoon.
A good west to east pressure gradient will set up each afternoon
and evening and there will be decent sw to w winds across the
foothills...mtns and deserts.
AT 16Z at KLAX... the inversion was around 1100 feet deep. The
top was near 2800 feet with a temperature of 25 degrees Celsius.
Overall... Low to moderate confidence in the 18z TAFs. The reduced
confidence is primarily due to the uncertainty regards the
location... timing... and intensity of the marine intrusion. The
marine clouds have almost completely pulled well off the coast.
The exception being a small area on and just off the coast of
Point Conception and some cloudiness over some of the Channel
Islands. There is a sixty percent chance of the marine intrusion
returning to the Central Coast and to some portions of the Los
Angeles County coast line overnight but the trend is for less
impact. Some windshear is expected near KSBA and hazy skies due to
smoke is possible in just about any area of the forecast area.
Otherwise and elsewhere VFR conditions will prevail.
KLAX... Low to moderate confidence in the 18z TAF. The reduced
confidence is primarily due to the uncertainty regards the
timing and intensity of the marine intrusion. There is a sixty
percent chance of the marine intrusion returning overnight but
the trend is for less impact. Otherwise VFR conditions will
KBUR...High confidence in the 18z TAF. VFR conditions will prevail
though with some haziness due to smoke.
A Small Craft Advisory has been issued to begin this afternoon for
increasing northwest winds and locally generated steep seas
expected over the outer waters from Point Sal to San Nicolas
Island. Small craft conditions will likely extend to all coastal
waters from Point Pierdas Blancas to San Nicolas Island by Monday
evening and will persist through at least early Thursday morning.
Gale force gusts are possible during the Monday and Tuesday
evening and overnight periods across all outer waters. Small
craft conditions will likely extend into portions of the inner
coastal waters from Point Piedras Blancas to Point Sal and the
western portion of the Santa Barbara Channel at times Monday and
Tuesday. There is a 30 percent chance of small craft conditions
mainly due to steep seas during this time from Point Mugu to
Patchy fog will prevail in the outer waters and along the Central
Coast through Wednesday morning with occasional development along
the coast south of Point Conception. Beginning Wednesday night and
Thursday morning low clouds and fog will become more prevalent
across the coastal waters.
Sundowner winds combined with temperatures 10 to 15 degrees above
seasonal normal and relative humidity in the teens will create
critical fire weather conditions in the Santa Barbara County
mountains and South Coast Monday late afternoon through Wednesday
morning. A moderate pressure gradient will develop Monday evening
and again Tuesday evening over Santa Barbara County between high
pressure in the southern portion of the San Joaquin Valley and
thermal trough of low pressure near shore. The stongest pressure
gradient between Bakersfield and Santa Barbara is expected Monday
night and then a slightly weaker gradient is expected Tuesday
night. Temperatures will likely be 10 to 15 degrees above
seasonal normal Monday then trend slightly cooler Tuesday.
Relative humidity will fall sharply Monday and then will change
little through Tuesday with little recovery in the wind prone
areas. Elsewhere elevated fire danger Sunday through Tuesday for
interior sections of Southwest California For the mountains,
interior valleys, and deserts, there will be significant warming
today, with the peak of the heat occurring Monday into Tuesday
when many areas will reach triple digit temperatures. Minimum
humidities will generally range between 10 and 20 percent during
this time, with isolated single digit readings possible in the
mountains and Antelope Valley on Monday and Tuesday. The warming
temperatures will cause steepening lapse rates that will enable
deep vertical mixing layers, especially on Monday and Tuesday when
mixing layer heights could range between 12,000 and 15,000 feet.
For existing fires or new ignitions over interior areas, plume
dominated fire behavior will be possible.
CA...Fire Weather Watch in effect from Monday afternoon through
Wednesday morning For zones 239-252. (See LAXRFWLOX).
PZ...Small Craft Advisory in effect from 3 PM this afternoon to 3
AM PDT Thursday For zones 673-676. (See LAXMWWLOX).