Area Forecast Discussion
Issued by NWS Los Angeles, CA
FXUS66 KLOX 301245
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
545 AM PDT SAT JUL 30 2016
Monsoonal moisture will bring a slight chance of thunderstorms to
the eastern mountains and the Antelope Valley today. A cooling
trend is expected through the weekend as high pressure weakens
aloft, with temperatures returning to near normal by Sunday.
Seasonable weather will then continue through mid week, then some
additional cooling is expected as a trough moves into the West
Coast. Night through morning low clouds and fog will continue to
affect coastal and some valley areas through next week.
Low clouds were widespread on the Central Coast and in the Santa
Ynez Valley again this morning. South of Pt Conception, stratus
was more patchy in nature, but there was still better coverage
than at this time on Friday across coastal sections of srn SBA
County and VTU County. There was also some locally dense fog
n of Pt Conception. Clouds should dissipate by mid morning in most
Low clouds pushed into southern and eastern Los Angeles County
earlier this morning, including into the San Gabriel Valley, but
have since pushed westward off the coast, possibly in response to
an outflow boundary approaching the region from the southeast.
That outflow was caused by what has been a cluster of
thunderstorms over Arizona which have since weakened. Surface
observations indicated gusty winds and reduce visibilities in
blowing dust across the deserts from Palm Springs south and east.
Dew points in these areas have also been on the rise. High
resolution models seem to pick up on some of this, and show dew
points rising to 13c to 16c at 850 mb across the mtns of L.A. and
eastern VTU Counties this afternoon. Models show fairly decent
instability over the mtns of L.A. and VTU Counties this afternoon.
With this influx of moisture, it appears that there will be a
slight chance of showers/tstms in the mtns this afternoon and
evening, and s to sw flow aloft could cause some of them to drift
into the Antelope Valley. Have added slight pops for these areas.
With the upper high weakening, heights will lower a bit across the
region. At the same time, onshore gradients will strengthen. This
should lead to 3 to 6 degrees of cooling in most areas today.
The upper high over and just to the east of the region will
slowly weaken tonight and Sunday, then change little on Monday.
The marine layer is expected to deepen a bit tonight, allowing
stratus to push into at least the lower valleys, with a bit more
deepening and inland penetration of the cloud Sunday night and
Monday. There should be a few degrees of cooling in most areas on
Sunday, bringing temps back to near normal levels in most areas.
Models actually show a bit of warming at 950 mb Monday afternoon,
so a degree or two of warming is possible, but any warming would
be very minor if it occurs. There will be some mid and high
levels moisture at times, particularly across eastern sections of
the forecast area, but at this point, expect just some buildups
each afternoon and evening.
The upper high will continue over srn CA Tue and Wed, so expect
mostly minor changes in night through morning low cloud coverage
or max temps. An upper trough will develop along the West Coast
Thu, and this should bring some cooling to most areas, with little
change Fri as the trough lingers along the coast.
At 1020z, the marine layer was around 1500 feet deep at KLAX. The
top of the inversion was near 4100 feet with a temperature around
29 degrees celsius.
LIFR to IFR conditions will likely spread into coastal terminals
through 13Z. The highest likelihood on LIFR conditions exists for
coastal terminals north of KOXR. Conditions should improve to VFR
between 15Z and 19Z.
KLAX...Low confidence with return of IFR/low MVFR cigs between
through 18Z. 40% chance for cigs to scour out up to 2 hours earlier
than 12z taf. Continued low confidence with timing of IFR/MVFR
cigs this eve. Could be a few hours either side of 09z.
KBUR...High confidence in VFR conditions through period.
Moderate to high confidence with the forecast through this
early next week. Winds will generally remain light to
occasionally moderate through the weekend. There is a 30% chance
that SCA level wind gusts could develop near Point Conception to
near San Nicolas Island Monday late afternoon and evening hours. A
shallow marine layer will continue widespread dense fog with
visibility 1 nautical mile or less for areas N of Point Conception
through this morning.
A small but long period southerly swell will develop Sunday into
Hot and dry conditions continue with widespread temperatures
currently in the 90s and 100s and relative humidities in the 10s to
low 20s across interior areas. Locally gusty onshore winds will
continue during the afternoon and evening hours across portions of
the Los Angeles Mountains into the Antelope Valley through at least
early next week. Gradually improving relative humidities and cooler
temperatures will help to reduce fire weather concerns including
over the Sand Fire this weekend into early next week as high
pressure aloft weakens and is gradually replaced by a weak low
pressure aloft off the coast of Northern California.