Scientific Forecaster Discussion
fxus66 klox 260008
Area forecast discussion...updated
National Weather Service Los Angeles/Oxnard California
508 PM PDT sun Aug 25 2019
Above normal temperatures will continue through much of the week
with increased humidity through Monday. Overnight and morning low
clouds will remain along the coast through Tuesday then may push
into some adjacent valley areas later in the week.
Short term (tdy-wed)...25/240 PM.
The marine inversion early this afternoon was around 600 ft deep
at lax. Low clouds persisted right along and off the central coast
early this afternoon, with some low clouds also lingering mainly
over the Santa Barbara Channel to the immediate S sba County and
vtu County coasts. The low clouds S of Point Conception should
thin out thru the afternoon, while little change is expected for
the central coast. Otherwise, mostly sunny skies will prevail
across the forecast area thru the rest of the day, altho a few mid
and high level clouds could start to push in from the S by
sunset. The NAM forecasts onshore gradients to be +6.9 mb lax-dag
late this afternoon which will help to keep locally gusty S-west
winds across the foothills, mtns and deserts into early evening.
High temps today will be about what they were yesterday and top
out about 2-5 degrees above normal away from the coast. The
warmest vlys and lower mtns will be in the 90s to near 100, while
the Antelope Vly will be in the low 100s.
For tonight and Mon, the forecast area will be under the southern
portion of an elongated upper level ridge extending from off the
nrn California coast thru central and sern California into Arizona. However, the
remnant upper level low from Tropical Depression Ivo will move up
from the S and just off the srn California coast thru Mon night and off
the central California coast on Tue. This is expected to slightly weaken
the upper level ridging over the forecast area on Mon with the
ridging pushing to the north and east into Tue. Even so, 500 mb heights will
remain rather high over swrn California and be in the 593-594 dm range
thru this evening, and in the 590-592 dm range for the most part
later tonight thru Tue. The upper level flow will be from the east
and southeast thru Mon then turn more to the S Mon night into Tue. Upper
level ridging is then expected to build back into srn California Tue night
and Wed with 500 mb heights increasing to 592-593 dm and the upper
level flow turning SW.
The marine inversion will likely remain surface-based at vbg and
be around 600-800 ft deep at lax tonight thru Mon, then deepen
perhaps a couple of hundred feet or so Mon night into Tue morning
and again Tue night into Wed morning. Low clouds and fog should
affect mainly the central coast along with the vtu/l.A. County
coast each night and morning thru Tue, then expand to the sba
County S coast and some of the adjacent vlys Tue night into Wed
morning. Patchy dense fog will be possible with any low clouds
along the central coast thru Tue morning as well. Otherwise,
generally fair skies will prevail tonight and Mon, with varying
amounts of mid and high level clouds from the remnants of Ivo
expected to move into the area from the S, then mostly clear skies
can be expected Mon night thru Wed.
Afternoon onshore gradients (lax-dag) are forecast by the NAM to
be around +7.3 mb Mon, +8.0 mb Tue and +7.6 mb Wed. These
gradients will continue to promote some gusty S to west winds each
afternoon and early evening across the foothills, mtns and
deserts. In addition, NAM forecast gradients from sba-smx will
lower to -2.1 mb this evening and -1.4 mb Mon evening, with
locally gusty sundowner winds possible each evening along the sba
S coast and Santa Ynez mtns, especially west of Goleta.
With decent warming in the boundary layer and at 950 mb, and high
1000-500 mb thicknesses (582-586 dm), temps away from the coast
are forecast to warm further Mon and Tue to about 5-12 deg above
normal. Temps should then cool slightly but remain several degrees
above normal for inland areas Wed. Highs for the warmest vlys and
lower mtns will be in the mid 90s to about 104 Mon and Tue, and
in the 90s to near 100 on Wed.
Long term (thu-sun)...25/240 PM.
The upper level ridging will build back into srn California Thu thru Fri
while strengthening into a 593-595 dm upper level high. The upper
level high should persist into Sat, then build back toward The
Four-Corners region for sun with 500 mb heights over swrn California lowering
slightly to 591-592 dm.
The marine inversion could be possibly up to 1000 ft deep Wed
night into Thu, then shrink to 500-800 ft deep or so Fri thru Sun.
Night and morning low clouds and fog are expected along the
central coast thru the period, and the vtu/l.A. County coast into
Thu morning, and just the l.A. County coast Fri thru sun.
Otherwise, mostly clear skies CA be expected across the forecast
area thru the extended period.
Temps will continue to be several degrees above normal away from
the coast Thu thru sun. Highs in the warmest vlys and lower mtns
should be generally in the 90s to near 100 each day, with the
Antelope Valley ranging from the upper 90s to around 102.
At 2335z at klax, the marine layer was 800 ft deep. The top of
the inversion was 1800 feet with a temperature of 26 c.
High confidence in inland tafs.
Low confidence in coastal tafs with a 40 percent chc of LIFR/IFR
cigs at sites with no cigs fcst and a 30 percent chc of no cigs at
sites with low clouds forecast. Cig arrival time could be off by 2
Klax...low confidence in taf. There is a 40 percent of bkn004
11z-15z. High confidence in no east wind component.
Kbur...high confidence in ceiling and visibility unlimited taf.
For the outer waters, moderate to high confidence in the
forecast. High confidence in winds and seas remaining below Small
Craft Advisory (sca) levels thru Wed. On Thu, there is a 60%
chance of Small Craft Advisory level winds during the afternoon and evening hours.
For the inner waters north of pt. Sal, moderate to high
confidence in the forecast. High confidence in winds and seas
remaining below Small Craft Advisory levels thru Wed. On Thu, there is a 30% chance
of Small Craft Advisory level winds during the afternoon and evening hours.
For the inner waters south of pt. Conception, moderate to high
confidence in the forecast. Conditions are generally expected to
remain below Small Craft Advisory levels thru Thu.
Patchy dense fog with visibility of one nautical mile or less is
across the coastal waters this morning and again during the late
night thru morning hours Mon and Tue.
A moderate southeast to south swell from former Tropical Storm Ivo
will affect the waters through early Tue. Swell will likely peak
between 3 and 5 feet. A swell from this direction could cause some
surges around and inside vulnerable harbors, especially Avalon
and San Pedro/Long Beach. Moderately large breaking waves near the
coast are possible, capable of capsizing small drifting boats.
Former Tropical Storm Ivo, currently about 450 nautical miles west-northwest
of Cabo San Lucas, will generate a southeasterly to southerly
swell which will bring elevated surf to south facing beaches
The peak of the swell across the coastal waters should occur this
afternoon through Monday morning at between 3 and 5 feet with a
period of between 11 and 14 seconds.
Surf heights are expected to average 4 to 6 feet on south facing
beaches of Los Angeles and Ventura counties. Dangerous rip
currents are likely, as are large breaking waves on rock jetties.
There is a low risk of minor tidal overflow near the times of
high tide on susceptible low lying beaches. The highest tides
will be late in the afternoon and evening today and Monday, and
should reach 5.7 to 6.7 feet. There may be some beach erosion as
Fire weather...25/315 PM.
A ridge of high pressure has built over the region and will
persist through much of this week. This will maintain very warm
conditions, with maximum temperatures generally in the 94 to 104
degree range over the valleys, mountains, and deserts. Minimum
humidities will generally range between 10 and 25 percent across
interior sections much of this week, with isolated single digit
readings at times in the Antelope Valley and Los Angeles County
mountains. Some mountain locations will also have moderately poor
overnight recoveries between 20 and 40 percent. Southwest to
northwest wind gusts between 20 and 30 mph will be common at times
over interior areas, with isolated gusts up to 40 mph near Lake
Palmdale. Northwest to north winds will generally gust between 20
and 30 mph each evening across the western portions of the Santa
Barbara South Coast and foothills, potentially increasing slightly
later in the week. All of this will result in elevated fire
weather conditions over interior areas much of this week.
California...beach hazards statement in effect through Tuesday morning for
zones 40-41-87. (See laxcfwlox).
Hazard potential outlook (wed-sun).
No significant hazards expected.