Area Forecast Discussion
Issued by NWS Los Angeles, CA

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000
FXUS66 KLOX 280101
AFDLOX

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
601 PM PDT Thu Jul 27 2017

.SYNOPSIS...

High pressure and onshore flow should keep fair skies in place
through the end of the week. Monsoonal moisture should move into
the region early next week and could bring possible thunderstorms
and showers in the afternoon and evening for the Ventura mountains
and Los Angeles valleys and eastward. The temperatures are
forecast to be around normal this week, with a warming trend next
week as the high builds in.

&&

.SHORT TERM...(TDY-SUN)

Overall, 12Z models in good synoptic agreement through the period.
At upper levels, ridge remains centered over the Texas Panhandle
area through Saturday as weak trough settles over the West Coast.
On Sunday, the center of the ridge moves westward, settling a bit
closer to the Four Corners area. Near the surface, generally
moderate onshore flow will prevail through the period.

Forecast-wise, no major issues through Saturday. With upper trough
settling over West Coast, there will be some lowering of H5
heights which should allow for some slight marine inversion
deepening. High resolution models indicate weak eddy circulations
developing the next couple of nights. So, will expect stratus to
be rather widespread across the coastal plain the next two
mornings and could squeeze into some of the lower coastal valleys.
Otherwise, skies should remain mostly clear through Saturday. As
for temperatures, there should be a degree or two of cooling for
most areas Friday and Saturday. The only other wrinkle for tonight
will be the possibility of some locally gusty northerly winds
across the Santa Ynez range and I-5 corridor. Nothing approaching
advisory-levels, but probably just enough to notice.

For Sunday, upper flow pattern turns a bit more southeasterly as
upper ridge moves westward and weak low develops over northern
Baja Mexico. So, some mid-level moisture could filter into the
area. With decent instability over the mountains, could be enough
to generate an isolated thunderstorm. PWATs are not too
impressive, but definitely enough to warrant continuation of
slight chance POPs over the Antelope Valley and Los Angeles county
mountains. Otherwise, there will be some stratus Sunday morning
across the coastal plain with increasing high clouds through the
day for all areas. As for temperatures, will expect some slight
warming for most areas on Sunday with some increase in H5 heights
and thicknesses.

.LONG TERM...(MON-THU)

Overall, 12Z models are in surprisingly good synoptic agreement
through the period. At upper levels, ridge gradually strengthens
with the ridge center setting up over Nevada and interior Central
California while a weak upper low spins off the Baja Mexico coast.
Near the surface, moderate onshore flow is forecast to continue.

Forecast-wise, main issues will be potential for monsoonal
moisture and temperatures. Given the forecasted upper level
pattern, an east to southeast flow will continue across the area
which should allow for some infiltration of monsoonal moisture.
So, there will be a threat of afternoon/evening thunderstorms
over the Ventura/Los Angeles mountains and Antelope Valley Monday
through Thursday. Additionally, models are still hinting at the
potential for an easterly wave Monday afternoon/night. So, will
keep some slight chance POPs in the forecast for the Los Angeles
county valley as well as the Ventura coastal valleys.

As for temperatures, the building upper level ridge will allow for
a warming trend for all areas through the period. By Wednesday and
Thursday, areas away from the coast will be in the mid 90s to low
100s.

&&

.AVIATION...28/0055Z.

At 18Z, the marine layer depth was around 950 ft. The top of the
marine inversion was around 1750 ft with a temperature of near 23
degrees Celsius. There was another inversion above up to around
4000 ft.

North of Point Conception...LIFR to IFR conditions will spread
into coastal terminals as soon as 03Z or as late as 10Z.
Conditions will become primarily LIFR between 07Z and 11Z, then
linger through 15Z before improving to VFR conditions between 17Z
and 18Z Friday.

South of Point Conception...IFR to MVFR conditions will spread
into coastal terminals through 13Z. Conditions should improve to
the VFR category between 16Z and 19Z Friday.

KLAX...There is a 70 percent chance of IFR to MVFR conditions
will spread into KLAX as soon as 06Z or as late as 13Z. VFR
conditions could delay until 20Z Friday, but more likely 17Z.

KBUR...VFR conditions are expected throughout the period. There
is a 30 percent chance of IFR to MVFR conditions between 13Z and
16Z but could occur as soon as 10Z.

&&

.MARINE...27/300 PM.

For the Outer Waters, moderate-to-high confidence in current
forecast. A small craft advisory remains in effect for the waters
near Point Arguello and Point Conception from late this afternoon
through late this evening. There is a 30-40 percent chance that
northwest winds could reach small craft advisory levels each
afternoon through Saturday evening, especially for the Northern
Outer Waters portion.

For the Inner Waters, high confidence in current forecast. For
all the waters, winds and seas are expected to remain below SCA
levels through Monday, except for local small craft advisory level
gusts across the Inner Waters each afternoon and evening.

A long-period southerly swell will spread into the coastal waters
between Friday night and Saturday, then a moderate-to-
occasionally large swell with a rather long period will affect
the waters from Saturday through weekend. The Santa Barbara
Channel will likely be blocked from the swell energy due to the
Channel Islands.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Beach Hazards Statement in effect from Saturday morning
      through Tuesday evening for zones 40-41-87. (See LAXCFWLOX).
PZ...Small Craft Advisory in effect until 3 AM PDT Friday for zone
      673. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK...(SUN-THU)

A high surf event should peak over the weekend as a long-period
southerly swell arrives at the Southern California beaches. High
surf and strong rip currents will occur through the weekend and
probably into late next week.

&&

$$

PUBLIC...Thompson
AVIATION...Hall
MARINE...Hall
SYNOPSIS...STu

weather.gov/losangeles



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