Area Forecast Discussion
Issued by NWS Los Angeles, CA
FXUS66 KLOX 250334
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
834 PM PDT SUN JUL 24 2016
High pressure across the southwest U.S. and onshore flow will
support near to slightly above normal temperatures through most of
the next seven days with a return of night to morning low clouds
to coastal and valley areas. An influx of monsoonal moisture may
bring thunderstorms across interior areas late next week.
It was significantly cooler in coastal and valley areas today.
Status has already returned to immediate beach areas from Ventura
County northward early this evening. The marine layer was running
around 900 feet deep this evening. Low clouds will overspread
coastal areas this evening, but will probably not reach far
interior sections of the coastal plain until after midnight.
The marine layer was a bit more shallow north of Point
Conception, so there could be some local dense fog on the Central
Coast, and there is a better than even chance that clouds will
not even reach the Santa Ynez Valley.
With the slightly deeper (although still rather shallow) marine
layer south of Pt Conception, the WRF suggests that stratus will
probably push into the San Gabriel Valley overnight, and possibly
into the lower portions of the Ventura County valley. There is a
chance that stratus could sneak into the San Fernando Valley by
daybreak, but confidence in this is low. Any clouds in the valleys
will clear by mid morning, and coastal areas should be clear by
Some mid and high level moisture pushing into Southern California
this evening may drift into eastern sections of Los Angeles County
later tonight and Monday. Precipitable water values rise to almost
1.4 across southern Los Angeles county Monday afternoon, and 850
mb dewpoints climb to 8 or 9 degrees C across eastern Los Angeles
county. Any increase in moisture looks to be confined to a rather
thin layer above 600 mb over eastern sections of the forecast
area. Still, would not be surprised if there were a few buildups
in the mtns of eastern Los Angeles County and the Antelope Valley
in the afternoon.
*** From previous discussion ***
Temperatures will remain near or slightly above normal tomorrow,
followed by several degrees of warming for inland areas on Tuesday
and Wednesday as high pressure over the Four Corners region starts
to expand west again. However, some mid and high level clouds
associated with a surge of monsoonal moisture could offset the
warming on Tuesday and Wednesday. The NAM suggests a surge of low-
level moisture (850 mb dewpoints greater than 8C) reaching
northern SLO County by Tuesday evening. However, most of the
moisture remains over the coastal waters and there is no
instability associated with it, so thunderstorms will not be an
issue through mid-week.
The main forecast concern in the long term will be the
possibility of monsoonal thunderstorms. The current forecast has a
slight chance starting on Friday for the LA/Ventura mountains and
the A.V., but based on the 850 mb dewpoints with the latest model
runs, it looks like the better chance for thunderstorms will be
over the weekend (still only a slight chance at this point
Temperatures will likely remain near or slightly above normal
through the end of the week, then some cooling will be possible
over the weekend with the increase in monsoonal moisture. An
easterly wave rotating around the southern fringe of the Four
Corners high may result in some lower height/thickness values as
.AVIATION...At 23z at KLAX, the marine later was around 900 ft deep.
The top of the inversion was near 2900 feet with a temperature of 28c.
Low clouds beginning to push into portions of the immediate
Central Coast this evening. The WRF indicates that stratus will
push into the central coast by mid evening, and into most areas of
the coastal plain by or shortly afternoon midnight. Expect conds
to be mostly IFR to LIFR, with local VLIFR conds possible,
especially across SLO and SBA counties. Clouds may just barely
squeak into the San Gabriel and San Fernando Valleys around
daybreak on Monday, but confidence in this is low and decreasing.
Skies should clear in most areas by late morning. Areas of smoke
will reduce vsbys to 3-5sm in the Antelope Valley and portions of
the L.A. Mountains, with local vsbys to a quarter mile or less.
KLAX...Moderate confidence in the 00z TAF. There is a 20 to 30
percent chance that cigs will not arrive until 11z.
KBUR...LOW Confidence in the 00z TAF. There is a 40 to 50 percent
chance that conds will remain VFR through the period.
Not expecting any small craft advisories through at least Wed.
There will be areas of dense fog with visibility 1 nm or less
across the northern two thirds of the outer waters and the
northern inner waters, with local dense fog elsewhere overnight
and Monday morning.
Red flag warning will be allowed to expire at 2200 PDT today.
A moderate onshore pressure gradient will become weak later
this evening and any winds will diminish.
The relative humidity trended 10-15 percent higher
and temperatures 10-15 degrees cooler than Saturday at this time.
Temperatures monday morning will differ little from this morning
and continue 5-10 degrees above normal. Temperatures will vary
plus or minus a couple of degrees each day and likely remain 5-10
degrees above normal through the week. RH will trend higher as
moisture pushes north through the period and overnight RH will
range 25-35 percent in the warmer interior sections with mid teens
in the afternoon. Slight chance of thunderstorms are expected over
the Ventura and Los Angeles County mountains Friday through Sunday
with a LAL of 2.
CA...Red Flag Warning in effect until 10 PM PDT this evening For
zone 254. (See LAXRFWLOX).