Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Los Angeles/Oxnard California
1032 am PDT Wednesday Jul 27 2016
the high will bring above normal temperatures inland this week.
A flow of monsoonal moisture will move in on Friday and over the
weekend as the high moves east. This may bring a slight chance
showers and thunderstorms to the Ventura and Los Angeles County
mountains and deserts. Then early next week the onshore flow will
increase for a cooling trend.
Shallow marine lyr has cleared off to the beaches at least and it
looks like another warm day for most areas. Forecast for today
looks good and not making any modifications. Main thing we'll be
looking at today is the potential for some convection as early as
Friday over the la/Ventura mtns. The early look shows scant
moisture but just enough instability to warrant concern,
especially for dry thunderstorms.
***From previous discussion***
Strong upper level high pressure over Nevada will move little
through Fri, so expect little change in the weather across the
region. Night through morning low clouds and fog should remain
confined to the coastal plain for the most part. Sely flow aloft
will continue to be favorable for transporting some mid level
moisture into the region, but all models show that any moist
layer will remain rather shallow and confined to elevations
above 600 mb. There could be some buildups in the mtns and
Antelope Valley each afternoon, but at this point, do not expect
any showers/thunderstorms. Do not expect much change in Max temps
on Thu and Fri, except for possibly just a couple of degrees of
cooling in coastal and some valley areas as onshore flow increases
The ec and GFS agree that the upper high will weaken and move
to the east over the weekend. Somewhat better moisture is
forecast to be transported into the forecast area, and while not
too impressive, the slight chance of afternoon and evening
showers and tstms for the l.A. And vtu County mtns and the
Antelope Valley looks reasonable for Sat and sun. Max temps will
likely be down a few degrees in response to the weakening upper
A weak trough will move across nrn CA on Monday, causing the upper
flow to turn swly, forcing any monsoonal moisture to the east
and ending any threat of tstms. Expect Max temps Monday and
Tuesday to be similar to those on Sunday in most areas.
At 18z, the marine layer was around 600 feet deep at klax. The
top of the inversion was near 4000 feet with a temperature around
27 degrees celsius.
North of Point Conception...moderate to high confidence in all tafs
during the upcoming forecast period. Persistence in play with a
shallow marine layer generating LIFR/IFR ceilings and visible at times
near the ocean while remaining sky clear inland.
S of Point Conception...low confidence in the next 24-hours.
Shallow marine layer in place, but stratus/fog has not been as
consistent except closer to the south Santa Barbara coast.
Anticipate areas of LIFR/IFR ceilings and visible moving back to the
Ventura and Los Angeles coastal tafs later tonight. Extent of
coverage is the limiting confidence factor. A few high-based
cumulus will be possible over the San Gabriel Mountains between
21-02z due to weak instability.
Klax...18z taf...VFR conditions expected through 08z. Low
confidence after that time frame for possible LIFR/IFR ceilings and
patchy MVFR visible as stratus develops near the beach early Thursday
Kbur...18z taf... high confidence in VFR conditions throughout
the forecast period.
High confidence wind forecast for the next few days as conditions
are not expected to change much through Friday. The marine
inversion remains shallow which will result in lingering dense fog
at times and poor visibilities across the outer waters, near the
northern Channel Islands, and in the Santa Barbara Channel. Weak
to locally moderate northwest winds will kick up each afternoon
near the islands and across the outer waters, with local gusts to
20 kts through the early evening hours.
Lower confidence on a persistent southerly swell due to eastern
Pacific tropical systems south of 25n this weekend. The forecast
may need to be adjusted to accommodate a continued south swell
mixing with northwest swell for Saturday and Sunday.
On track for another hot and dry day with similar conditions to
yesterday for interior areas, with breezy onshore winds across
southwest California transitioning to locally gusty northwest
winds across the I-5 cooridor into the western Antelope Valley
tonight. Relative humidities are currently in the 10s to lower 20s
across the Antelope Valley and at higher elevations. Temperatures
are expected to be down 2-4 degrees across interior areas today
with a slight increase in relative humidity. Areas with breezy to
gusty onshore winds mainly across the la mountains into the
Antelope Valley may experience a few hours of critical fire
weather conditions. Slight cooling today will lead to a slightly
lower mixing layer of about 13000 feet across the interior
portions of the Los Angeles County mountains, near the eastern
flank of the sand fire. This would still support the development
of a potentially significant pyrocumulus cloud in that region
again today if the sand fire remains active.
Elevated fire weather conditions across the interior mountains and
valleys including the location of the sand fire will persist each
afternoon and early evening through Thursday or Friday due to low
relative humidities and locally gusty onshore to northwest winds.
Northwest winds are expected to peak across the I-5 cooridor and
western Antelope Valley Wednesday and Thursday nights with gusts
up to 40 mph. A weak to moderate sundowner is possible Thursday
evening for the western Santa barabara South Coast and the Santa
Ynez range with local wind gusts to 35 mph. Additionally,
substantial drying aloft may bring single digit minimum relative
humidities to the interior mountains (and Santa Ynez range) above
about 2000 feet including far interior areas feet Thursday
possibly extending into Friday. This combination of low minumum
relative humidities and gusty winds across the I-5 coordior,
western Antelope Valley and western Santa Barbara South Coast may
support a few hours of critical conditions Thursday evening.
Elevated fire weather concerns extend into the upcoming weekend
due to the possibility of afternoon thunderstorms across interior
areas as high pressue weakens and shifts east, opening the door
for push monsoon moisture from the southeast.