High Surf Advisory 15, NWS Los Angeles, CA

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
249 PM PDT Sun Jul 9 2017

.SYNOPSIS...

The upper high will slowly weaken over the next couple days.
Onshore flow will return and kick off a cooling trend across the
area. Monsoonal flow may bring showers and thunderstorms to the
mountains and deserts today and Monday. After a brief cooling
trend midweek, conditions will again warm by next weekend

&&

.SHORT TERM...(TDY-WED)

Latest radar indicated organized showers starting to pop up
across the interior San Gabriel mountains and interior Ventura
County mountains. Latest visible satellite imagery continued to
show mid-level clouds increasing from the southeast, associated
with monsoonal flow. It also showed areas of smoke from area fires
streaming northward, affecting portions of Santa Barbara and San
Luis Obispo Counties. A weak disturbance embedded in the monsoonal
flow, currently just south of San Diego will continue to drift
westward into the coastal waters through this evening. Increased
instability associated with this feature will support the slight
chance of thunderstorms across southern waters extending into the
coast and valleys south of Point Conception as well as the Santa
Ynez and Cuyama Valleys with a slight chance to chance of
thunderstorms across the mountains into Antelope Valley.

The main threat with afternoon into evening thunderstorms would be
winds gusty up to and locally over 50 mph and heavy rain. In fact,
weak easterly to northeasterly steering winds aloft and
precipitable waters increasing to around 1.5 inches combined with
moderate instability could lead to localized flash flooding,
especially across the eastern LA mountains into the Antelope
Valley. Thunderstorms that form across the mountains may drift
into adjacent coastal and valley areas today with the weak east
to northeasterly steering currents aloft.

High temperatures so far today have been close to forecasted
except for areas affect by smoke by multiple fires north of Point
Conception as the combination of smoke and increased cloud cover
(likely in part due to the smoke) have kept down a bit more then
expected. As the ridge of high pressure loosens its grip over the
area, expect cooler temperatures overnight tonight, although
increases in moisture and cloud cover from monsoonal flow will
still maintain above normal low temperatures for many areas,
especially to the south of Point Conception.

The ridge of high pressure is expected to continue to weaken and
shift eastward towards the Central and Eastern United States
through Wednesday. This combined with a weak trough of low
pressure setting up off the West Coast will switch the
southeasterly to southerly flow, southwesterly by Tuesday, acting
to shut the door to monsoonal flow and any associated thunderstorm
activity. As for Monday, it does appear there will be enough
moist southerly flow and instability to warrant a slight chance of
thunderstorms for the Mountains into the Antelope Valley. Other
than afternoon and evening build-ups, skies will become mostly
sunny by Tuesday and continuing into Wednesday, save for night to
morning low clouds redeveloping for coastal areas by Wednesday.

The increasing dry southwesterly flow aloft and lowering 500 mb
heights will support generally 4 to 8 degrees of cooling (largest
away from the coast) for Monday with a few degrees of cooling
heading into Tuesday and Wednesday with temps approaching normal
by Wednesday. Low temps will also follow a similar cooling trend
with most significant cooling also away from the coast. The
prolonged cooling trend should put an end for the need for heat
products, for now.

.LONG TERM...(THU-SUN)

There is above normal confidence in terms of the large scale
pattern for the long term. High pressure aloft will likely expand
back over Utah by Friday, strengthening and expanding further
westward, possibly into the Great basin by Saturday with little
change for Sunday. This means our break from the latest heatwave
may be short lived with widespread triple heat possibly returning
next weekend. Increasing northerly gradients next weekend may
further add to the heat and help maintain warm overnight
temperatures for favored valley and foothill locations.
Additionally, the high position over the Great basin will open the
door once again for monsoonal moisture with increasing humidities,
mid to high level clouds, as well as thunderstorms possibly
returning to portions of Southwest California.

&&

.AVIATION...09/2130Z.

At 21Z, the marine layer was around 500 feet deep at KLAX. The
top of the inversion was around 1300 feet with a temperature of
28 degrees Celsius.

Moderate confidence in the current forecast. VFR conditions are
expected throughout the period, except for a chance of LIFR to IFR
conditions at coastal terminals after 04Z. Smoke at times may
product There is a slight chance of thunderstorms at all
terminals through 04Z.

KLAX...VFR conditions are expected throughout the period, except
for a 30 percent chance of LIFR to IFR conditions between 10Z and
16Z. There is a slight chance of thunderstorms at all terminals
through 04Z.

KBUR...High confidence in VFR conditions throughout the period.
There is a 20 percent chance of a thunderstorm through 04Z.

&&

.MARINE...09/300 PM.

Winds will subside tonight and Small Craft Advisories will likely
expire at 9 pm PDT this evening. Locally choppy seas may still
persist through much of the week due to short-period seas and
local Small Craft Advisory winds each afternoon and evening.

A moderately long-period southerly swell originating from
Hurricane Eugene, about 550 miles south-southwest of Cabo San
Lucas, will move over the waters through Thursday.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Heat Advisory in effect until 11 PM PDT this evening for
      zones 36>38-44>46-51>54-59-88-547. (See LAXNPWLOX).
     Beach Hazards Statement in effect through Wednesday evening
      for zones 40-41-87. (See LAXCFWLOX).
PZ...Small Craft Advisory in effect until 9 PM PDT this evening
      for zones 670-673. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK...(WED-SUN)
A south swell from hurricane Eugene will likely bring elevated
surf with strong rip currents to south facing beaches Tuesday and
Wednesday. Well above normal temperatures will likely return late
next week with a possible return of monsoonal driven
thunderstorms.

&&

PUBLIC...Munroe
AVIATION...Hall
MARINE...Hall
SYNOPSIS...Sweet

weather.gov/losangeles