Scientific Forecaster Discussion
fxus66 klox 261056
Area forecast discussion
National Weather Service Los Angeles/Oxnard California
356 am PDT Mon Jun 26 2017
an upper level trough off the California coast will weaken high
pressure aloft starting this afternoon and bring a cooling trend
as onshore flow strengthens. One more day of very warm
temperatures expected inland before cooling down to more normal
highs for this time of year by midweek. Expect low clouds and fog
to redevelop after today and continue through the week.
Latest fog product imagery indicated clear skies across the
coastal waters and most of the forecast area. There was some
patchy low clouds lingering around vandenberg to Lompoc and looks
like just crossing into the Santa Ynez Valley. This stratus should
be short lived this morning. Low clouds will slowly make there
way into our northern coastal waters later today. Not much in the
way of smoke from the placerita fire showing up on satellite
overnight and into this morning which is probably a good thing,
showing the flames are laying down the smoke plume was quite
impressive on yesterday's visible satellite imagery. Expect some
patchy smoke around the Santa Clarita valley this morning, and
should advect towards the Antelope Valley in the afternoon due to
the SW winds expected.
One more day of very warm to hot conditions across inland areas,
especially the Los Angeles County valleys, mountains and Antelope
Valley. The hottest areas are likely to be the western portion of
the San Fernando Valley around 105 degrees with the Santa Clarita
valley also likely to experience lower triple digit heat along
with the Lower Mountain elevations. Heat advisories were issued
to cover the la/vtu County mtns as well as the San Fernando and
Santa Clarita valleys through this evening. The San Gabriel valley
will be warmer than normal, but only a few locations should reach
the upper 90s to around 100. Most inland areas will be 4 to 6
degrees cooler today with coastal areas remaining about the same
as yesterday. Coastal areas will remain quite mild today with
highs in the upper 60s and 70s...except into the upper 80s for the
la basin. T
Going back to yesterday's heat anomaly for the San Fernando
Valley where most of the valley's highs ranged from the 105 to 111
degrees was caused by northerly flow across the I-5 corridor
lasting longer into the afternoon and spilling across the scv and
sfv. The downsloping affect helped high temps soar several degrees
warmer than what was forecast. This happens now and then and even
the high resolution models don't pick up on this. 950 mb temps
will be a few degrees cooler across the Antelope Valley, while
they remain about the same for the la/vtu County valleys. The
difference is we are expecting a slightly stronger onshore flow
today with more of a SW to west wind pattern to keep high temps from
soaring to where they were yesterday.
A red flag warning was issued last evening valid this morning
through this evening as well due to the stronger onshore winds
expected across the Highway 14 corridor through the Soledad Pass
and into the Antelope Valley and adjacent foothills. The GFS is
advertising near Wind Advisory thresholds, but think it's a bit
overdone. But expect local gusts to 45 mph around Lake Palmdale in
the afternoon. The combination of the stronger winds, very low
relative humidities and continued triple digit heat was the reason
why it was issued for the la mtns, Santa Clarita and Antelope
For tonight, low clouds should become more widespread across the
coastal waters except a weak-moderate sundowner is expected across
the sba South Coast and adjacent foothills this evening. With the
upper ridge beginning to flatten a bit, but still in tact across
the southern portion of the state, the marine layer will continue
to be shallow with a strong inversion. Expect low clouds to affect
the central coast with patchy dense fog and should make it into
the la County coast, but could struggle to move north into Ventura
County. Expecting sba South Coast to remain mostly clear due to
the northerly winds overnight. There should be some relief of warm
overnight temperatures finally across inland areas.
Tue and Wed the upper ridge lingers over the region, but it
weakens as an upper trough moves across much of the West Coast
both days. The combination of stronger onshore gradients, cooling
boundary layer temps and a deeper marine layer, will bring
widespread cooling across the entire forecast area with best
cooling across la/vtu counties. High temps will be just above
normal for this time of year, with the Antelope Valley finally
going below 100 after a number of days well into triple digit
heat. Valleys will be in the 80s for the most part, with a few
lower 90s across warmest locations. Wednesday should be the
coolest day of the week with high temps right where they should be
for most areas. Night through morning low clouds will continue and
likely reach the coastal valleys from Tue night through much of
Looking fairly uneventful through the long term. Both the GFS and
European model (ecmwf) are in good agreement with large scale features through the
long term period. Overall, there will be weak troughing across
much of California with a building ridge off to the SW. It looks
like it will have enough strength to throw a 591 dm high over
socal briefly Friday before it weakens and northwest flow aloft persists
into the weekend. So expect similar conditions Thursday from
Wednesday with minor temperature fluctuations, then a brief modest
warming for Friday, with a modest cooling trend into the weekend.
Overall, not much change. Expect night through morning low clouds
to continue across coast and likely some coastal valleys into late
this week and weekend.
At 0530z at klax... the inversion was around 500 feet. The top of
the inversion was around 2900 feet with a temperature of near 32
Overall... moderate confidence in the current coastal tafs and
high confidence in the interior tafs. Patchy low clouds and fog
will develop along the coast overnight... primarily along the
central coast. There is a thirty five percent chance of mfr
conditions developing toward daybreak and a ten percent chance of LIFR/IFR
conditions. Any reduced conditions will improve to VFR by 18z.
Otherwise and elsewhere VFR conditions will prevail.
Klax... moderate confidence in the current tafs. There is a
thirty percent chance of patchy low clouds and fog developing in
the terminal vicinity and a ten percent chance of mfr conditions
developing toward daybreak. Any reduced conditions will improve to
VFR by 18z. Otherwise VFR conditions will prevail. No east winds
greater than seven knots are expected during the forecast period.
Kbur... high confidence in the current tafs. VFR conditions will
prevail throughout the period.
For the outer waters... Small Craft Advisory (sca) level
conditions will continue through at least Tuesday evening. Wind
speeds may weaken to below Small Craft Advisory levels during the morning hours but
will strengthen again in the afternoon.
For the inner waters... Small Craft Advisory level winds will develop in the afternoon
and evening hours through Tuesday evening across the northern
nearshore waters as well as in the Santa Barbara Channel. Local
gusts up to 25 kt could also develop during this time from Point
Mugu to San Mateo Point west of Santa Catalina Island.
In addition to the elevated winds, a short period west to
northwest swell could impact the coastal waters through
Fire weather...26/345 am.
Continued hot and dry conditions with stronger gusty winds,
especially across the Highway 14 corridor. Has warranted issuing
a red flag warning for the Los Angeles mountains, Santa Clarita
valley and the Antelope Valley valid this morning through this
evening. Although there will be a slight cooling trend today
across inland areas, very dry conditions are likely to persist
into Tuesday. The hot and unstable conditions will bring the
potential for plume dominated fires which can create their own
intense winds. Gusty west to southwest winds will impact the
Highway 14 corridor through this evening. For Los Angeles County,
the strongest winds will be in the I-5 corridor in the mountains
as well as the Antelope Valley foothills with gusts between 30 to
40 mph. Humidities in the single digits to teens are expected
across the mountains, deserts, and interior valleys.
For Santa Barbara County, sundowner winds will affect the western
portions of the Santa Ynez range and South Coast (mainly from
Gaviota to goleta), with gusts of 30 to 40 mph each evening
through Tuesday. In addition, localized humidities falling to
between 15 and 25 percent can be expected in the Santa Ynez
Mountains and adjacent canyons where the downslope sundowner winds
The combination of hot and dry conditions with locally gusty winds
will bring elevated fire weather concerns to interior sections
once again on Tuesday. If fire ignition occurs, dangerous fire
behavior should be expected. As such, the public should be extreme
careful when handling potential ignition sources such as
cigarettes, campfires, hand torches and metallic Weed trimmers.
California...heat advisory in effect until 9 PM PDT this evening for zones
53-54-88-547. (See laxnpwlox).
Red flag warning in effect from 9 am this morning to 9 PM PDT
this evening for zones 254-259-288. (See laxrfwlox).
Pz...Small Craft Advisory in effect until 3 am PDT Wednesday for
zones 645-650-670-673-676. (See laxmwwlox).
Hazard potential outlook...(wed-sun)
no significant hazards expected.