Weather Service Report


020 
FXUS66 KLOX 160429
AFDLOX

Area Forecast Discussion...UPDATED
National Weather Service Los Angeles/Oxnard CA 
929 PM PDT Sun Jul 15 2018

.SYNOPSIS...15/553 PM.

Temperatures will remain hot across the region through at least
another week though onshore flow will provide some overnight and
morning relief along the coast. There is a slight chance of
thunderstorms Wednesday and Thursday afternoon across the Ventura
and Los Angeles County mountains and the Antelope Valley.

&&

.SHORT TERM (SUN-WED)...15/929 PM.

High pressure aloft remains in place near 31N and 128W this
evening and this feature will remain a staple of the forecast for
this week. Above normal temperatures are likely to persist through
this week. Models continue to show some cooling at 950 mb on
Monday, but it is debated if much cooling will develop as 500 mb
heights remain virtually the same. Closer to the surface, onshore
flow and a marine layer remain in place this evening. The latest
AMDAR soundings indicate a marine layer depth near 1000 feet at
KLAX this evening and some deepening should take place overnight
and into Monday morning to around 1500 feet or so. With warmer
ocean temperatures climbing into the 70s in the Santa Monica Bay,
stratus formation looks to remain problematic again tonight and
into Monday. Stratus may be patchy at best.

An update will be issued to the forecast shortly. 

***From Previous Discussion***

Monday night into Tuesday an easterly wave of monsoon moisture 
slides across far southern California, but our area should remain 
convection-free and at best some high cloudiness may skirt Los 
Angeles County Tuesday morning. However, another wave slides 
across the area Tuesday night and Wednesday. This one has been 
consistently showing more cloud cover and a slight boost in 
instability over the mountains and desert for the last couple of 
days now. Expect partly to mostly cloudy skies with an increase in
humidity on Wednesday. Will continue the idea of a slight chance 
of afternoon/evening thunderstorms for the Ventura and Los Angeles
County Mountains as well as the Antelope Valley. With enough 
cloud cover hampering solar radiation there will likely be a 2-4 
degree cool down on Wednesday. The marine layer should shrink as 
the week progresses with less and less morning stratus for coastal
areas.

.LONG TERM (THU-SUN)...15/110 PM.

The long term through next weekend and beyond continues to look 
hot and there is the potential for a long-duration heat wave from
day8 to ?? High pressure expands eastward and centers over the 
4-corners late in the week. This doesn't provide much of a monsoon
thunderstorm risk for our region as the flow turns more 
southerly, but will continue with a slight chance in the 
mountains/desert on Thursday as this pattern evolves after this.
Highest temperatures will be 100 to 107 degrees in the inland
valleys and desert on Sunday afternoon. 

By Monday, July 23rd, a 598dm high pressure center sits over the 
high desert area of southeast California. There are good 
indications that this giant high will not move much at all 
through the end of July! By Monday our 950mb temperatures will be 
close to 35 degrees C for inland valleys and 40 C in the desert. 
Although this doesn't appear to be a repeat of the early July 
heat wave when some temperatures reached 117 degrees in the San
Fernando Valley, it definitely looks like a very long duration 
event that builds and compounds heat impacts over time.

&&

.AVIATION...16/0102Z.

At 00Z, the marine layer depth was around 1300 feet deep at KLAX.
The top of the marine inversion was around 2000 feet with a 
temperature of 24 degrees Celsius. There was another inversion up
to around 5100 feet.

Low to moderate confidence in the current forecast, except high
confidence in the forecast for desert terminals.

South of Point Conception, IFR to MVFR conditions will likely spread
into the coastal terminals through 13Z. Higher confidence in MVFR
conditions south of KNTD. VFR conditions should be slightly slower
to develop Monday, possibly not clearing until two to four hours 
later than forecast.

North of Point Conception, LIFR to IFR conditions will spread into
coastal and lower valley terminals through 13Z. Conditions will 
likely deteriorate to LIFR after 05Z. VFR conditions should be
slightly slower to develop on Monday.

KLAX...There is a 70 percent chance of MVFR conditions developing
at KLAX between 06Z and 18Z. There is a 30 percent chance that
MVFR conditions could linger until as late as 21Z.

KBUR...VFR conditions are expected throughout the period. There is
a 20 percent chance of MVFR visibilities between 13Z and 16Z.

&&

.MARINE...15/157 PM.

Across the Outer Waters, moderate to high confidence in Small 
Craft Advisory level winds and steep seas through late tonight,
though conds may drop below SCA levels as early as this evening,
such as zone 670 which now lasts until 9 pm. There is a 30% 
chance of SCA level winds across the southern two thirds of the 
outer waters mainly near Pt Conception Mon afternoon and evening. 
SCA conditions are not expected Tue thru Thu.

For the nearshore waters north of Point Conception, low to moderate
to confidence in the forecast for today. There is a 40% chance of
percent chance of SCA level winds this afternoon and evening. 
Otherwise, SCA conds are not expected Mon thru Thu.

Across the inner waters south of Point Conception, conditions are
expected to remain below Small Craft Advisory levels thru Thu,
with just a 20-30% chance of SCA level winds across western
portions of the SBA Channel late this afternoon and evening.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...Small Craft Advisory in effect until 3 AM PDT Monday for
      zones 673-676. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK (WED-SUN).

An influx of monsoonal moisture could bring shower and
thunderstorm activity and a threat of localized flooding to the 
mountains and desert Tuesday night through Thursday. Building heat
for inland valleys, mountains, and the desert through Sunday.

&&

$$

PUBLIC...Hall/Boldt
AVIATION...Hall
MARINE...Sweet
SYNOPSIS...Kj

weather.gov/losangeles

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Western Regional Climate Center, wrcc@dri.edu