Small Craft Advisory 85, NWS Los Angeles, CA

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
1146 PM PDT Tue Jun 13 2017

.SYNOPSIS...
A building ridge of high pressure will support continued warming
to the area through early next week. Increased onshore flow will
bring a return of night to morning low clouds and patchy fog to
some coastal areas and provide some relief from the heat for some
coastal areas this weekend.

&&

.SHORT TERM...(TUE-FRI)

The latest fog product imagery indicates only patches of low
clouds and fog this evening along some beaches. A weak marine
inversion remains over the area this evening, but some semblance
of a marine layer should develop toward daybreak Wednesday,
especially for the Los Angeles County and Central Coasts. High
pressure aloft over the Northern Mexico should start to take hold
of the weather pattern and strengthen the marine inversion albeit
shallow. NAM-WRF boundary layer relative humidity indicates some
higher values in excess of 80 percent approaching the Los Angeles
County Coast and Central Coast. Patchy low clouds and fog will be
added to the forecast for these areas.

High pressure aloft will build in over the next several days
bringing a sharp warming trend and daytime temperatures well
above normal by Thursday. The marine layer depth will likely
remain quite shallow and confined mainly to the coastal areas.
The best chance of any stratus cloudiness is for the beaches and
immediate coastal areas, although some farther inland penetration
cannot ruled out as the onshore gradients could increase into the
weekend. Heat products may be needed as the event grows closer and
future shifts will be briefed about the heat risk probabilities.

A few tweaks will be made to the forecast and an update will
issued shortly.

*** FROM PREVIOUS DISCUSSION ***

Both Thu/Fri nights we're expecting to see an increase in
northerly flow across the western part of the forecast area,
leading to a slight increase in Sundowner winds, possibly close to
advisory levels. Models aren't yet showing too much of a surface
gradient so it's not certain whether the winds and hot temps will
surface at the beaches or stay primarily in the foothills. But
there is the potential for temps to spike into the high 80s in the
SB area later this week.

Overall temps will warm to 12-18 degrees above normal by Friday.
Beaches will still be getting a decent enough sea breeze to
moderate temps there but warmer valleys expected to get close to
triple digits and far inland areas like the Antelope Valley and
interior SLO/SBA counties could approach 105.

.LONG TERM...(SAT-TUE)

Hot weather to continue through the period and perhaps beyond.
Models continue to advertise a 1-2mb increase in onshore flow over
the weekend that should temporarily bring a halt to the warming
trend for coast/valleys, but temps will still be well above
normal. For next week, models slightly changed their tune after
Monday, now showing the ridge flattening out a bit as a weak
trough hits the Pac. NW. This appears to have little impact as
heights remain about the same and thicknesses actually climb
slightly all the way through Wednesday. Similarly, 950mb temps
also rise Tue/Wed so for now will continue with the idea that most
areas will resume the warming trend early next week with the
hottest days likely Tue/Wed, which is exactly a year after last
year's heat wave which set a number of daily high temperature
records in the area that will be very tough to beat. Will have to
consider at some point in the next couple days issuing an
excessive heat watch for interior areas, mainly lower elevation
mountains, Antelope Valley, any possibly interior SLO/SB Counties.
While temps in the coastal valleys will approach or locally exceed
100, overnight lows are expected to remain in the 60s for the most
part providing at least some relief.

&&

.AVIATION...

14/0630Z

At 06Z at KLAX, the marine layer depth was near 1000 feet. The
top of the inversion was 1600 feet with a temperature of 23
degrees C.

High confidence in CAVU TAFs except for KSMX and LGB which have a
30 percent chc of IFR conds 11Z-16Z and KLAX and KSMO which have a
20 percent chc of IFR conds 11Z-16Z.

KLAX...Good confidence in TAF. There is a 20 percent chc of IFR
conds 11Z-16Z. There is a chc of a 5kt east wind component 11Z-
15Z.

KBUR...Very high confidence in CAVU TAF.

&&

.MARINE...

13/800 PM

Moderate to high confidence in gales across the outer waters
through late tonight...and likely through late Wednesday night
over the two northern outer zones. South of Santa Rosa Island,
winds are expected to subside below gale-force late tonight. Over
the northern inner waters, moderate to high confidence in SCA
conditions during the afternoon to evening hours each day through
the weekend.

Across the SBA Channel, winds will remain at SCA level through
around midnight, but short period seas will persist through late
tonight. There will be a chance of SCA conditions during the
afternoon to evening hours again on Wednesday and
Thursday...strongest over the western section.

Over the southern inner waters, winds and seas are expected to
remain below SCA level through the weekend.

Ses will remain short period and choppy for all waters through the
weekend. Patchy dense fog may also become a concern by Wednesday
night.

&&

.FIRE WEATHER...

13/230 PM

High confidence in extended period of elevated fire danger across
interior sections of Southwest California today through early
next week due to prolonged period of hot and dry conditions along
with drying fuels. Weak offshore flow this morning has brought
significant warming and drying to interior sections today, with
humidities lowering to between 10 and 20 percent.

The heat wave is expected to build through the week and persist
through at least early next week, with widespread readings into
the 90s across inland areas. Triple digit heat will become likely
at times Friday through early next week across the Antelope
Valley, as well as warmest interior valleys, and lower mountains.
The hot and unstable conditions later this week into early next
week could lead to plume dominated fire potential, especially in
the foothills and mountains.

Many interior sections will see humidities fall into the teens
and single digits each day during this heat wave. Starting
Wednesday night, there will be warm overnight low temperatures and
poor humidity recoveries in the foothills and mountains that
would enable active burning at night in these areas. During this
extended period of hot and dry weather, there will be elevated
fire danger through at least early next week across interior
sections, with the greatest threat being potential rapid spread
of fires in grasses and other fine fuels. From Saturday through
Monday, there will likely be increased onshore winds through
the Highway 14 corridor from the Santa Clarita Valley to Antelope
Valley, increasing the large fire potential for this region.
Another area of concern will be locally gusty sundowner winds
Thursday evening and Friday evening across the Santa Barbara
South Coast and Mountains.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...Small Craft Advisory in effect until 3 AM PDT Wednesday for
      zones 645-650. (See LAXMWWLOX).
     Gale Warning in effect until 3 AM PDT Thursday for zones
      670-673. (See LAXMWWLOX).
     Gale Warning in effect until 3 AM PDT Wednesday for zone 676. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK...(FRI-TUE)
Hot, dry and gusty sundowner winds possible in southern Santa
Barbara County Fri night. Hot temperatures 12-18 degrees above
normal are expected, mainly for interior sections Friday through
Tuesday.

&&

PUBLIC...Hall/MW
AVIATION...Rorke
MARINE...Smith
FIRE...Gomberg
SYNOPSIS...Munroe

weather.gov/losangeles