Area Forecast Discussion
Issued by NWS Los Angeles, CA

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000
FXUS66 KLOX 270630
AFDLOX

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
1130 PM PDT Mon Jun 26 2017

.SYNOPSIS...
High pressure aloft over the region will weaken over the next
several days as an upper-level trough over the Pacific Northwest
brushes the area. A cooling trend will develop through Thursday as
onshore flow strengthens and the marine layer deepens. A more
persistent stratus deck will become a staple of the weather
pattern for the coastal and valley areas through Thursday,
possibly lingering at the beaches throughout each day.

&&

.SHORT TERM...(MON-THU)

Another hot day across interior portions of the forecast area
with several stations once again reporting triple digit readings.
A few of the hottest locations included Woodland Hills and
Northridge reaching 106 degrees, and Chatsworth and Van Nuys at
104 degrees. Warm temperatures continue this evening across
interior areas, as well as portions of the SBA south coast and
Santa Ynez mountains where gusty sundowner winds are occurring.
As of 8 pm, current SBA-SMX gradient at -4.4 mb. Not much in the
way of upper level wind support, so thinking that the winds
should generally remain below advisory levels, gusting in the 30
to 35 mph range, except local gusts around 40 mph near Refugio
Hills. Temperatures will spike to around 90 degrees this evening
in favored downslope locations bringing another round of elevated
fire weather concerns to that area.

Heat advisories will likely be allowed to expire at 9 pm, as
cooling trend expected to keep most interior areas in the 90s on
Tuesday. Marine layer clouds expected to fill in across the
Central Coast tonight as well as the Salinas River Valley, with a
slight chance that some low clouds and fog could reform along the
immediate portions of the LA county coast. Increasing onshore flow
and a strengthening eddy circulation will likely bring a
substantial increase in low clouds and fog across coastal/valley
areas on Tuesday night.

*** From previous discussion ***

Still a decent northwest gradients across the Santa Ynez range the
next couple night but minimal support aloft. So for the most part
winds should remain below advisory levels. The northwest flow and
warm air mass will help keep south coast temps in the 80s Tuesday
and possibly even near 90 in some isolated spots.

.LONG TERM...(FRI-MON)

A little ridge will pop up Friday to help push temps up a few
degrees in most areas but the warm up will be brief as weak
troughing returns for the weekend. Still a little uncertainty with
this though as models have sort of been bouncing around with the
weak trough/ridge scenario. Probably not a huge difference either
way as temps should remain within a few degrees of normal through
early next week.

&&

.AVIATION...

27/0600Z

At 0545Z at KLAX...There was a weak 450 ft marine layer. The
inversion top was 1800 ft with a temperature of 28 degrees
Celsius.

KSBA and south...high confidence in all CAVU TAFs.

The cig/vis change timing could be off by as much as 2 hours for
the KSMX and KSBP forecasts.

KLAX...High confidence in VFR conditions through 08Z, with a 20
percent chance of IFR conditions mainly from 10-17Z Tuesday. West
wind gusts between 20 and 25 KT likely through 03z. No
significant east winds expected through Tuesday.

KBUR...High confidence in CAVU TAF.

&&

.MARINE...

26/800 PM.

High confidence in SCA conditions with gusty NW winds and short
period seas at least through Thursday over the outer waters. Winds
are expected to strengthen on Tuesday with speeds up to 30 knots
over much of the area. The SCA extends through late Tuesday night
but conditions are expected to remain hazardous through Thursday
or Friday...and possibly longer over the northern waters.

Moderate confidence in SCA conditions over the Santa Barbara
Channel and Santa Monica Basin through tonight...with similar but
slightly weaker winds on Tuesday. The stronger winds will
generally be over the western portions of the inner waters and
will likely persist through Tuesday night...along with short
period seas. There will be lulls of several hours each morning
within about 10 miles of the coast.

Two wave groups will be observable over the waters, with a long
period (13-15 seconds) south to southwest swell through Tuesday,
and a short period (6-8 second) west swell and/or wind wave. The
buoys may highlight the long period swell, but the short period
swell will be the most noticeable and the most hazardous. Later
this week the short-period west swell will dominate as the south
swell fades.

&&

.FIRE WEATHER...

26/800 PM.

Several small fire starts across the forecast area today as gusty
onshore winds coupled with continued hot and dry conditions across
inland areas. A large fire called the Hill Fire in SLO County
(located to the east of Santa Margarita) has spread rapidly to
900 acres as of 8 pm. Gusty onshore winds will continue to spread
the fire and smoke plume eastward this evening. The low level
winds in this area will diminish overnight then shift to a light
north to northeast direction on Tuesday morning. Elevated fire
weather concerns will then return to the fire area on Tuesday
afternoon as gusty onshore winds combine with very warm and dry
conditions in the afternoon and evening hours. The 00z Vandenberg
sounding showing the marine layer depth around 1100 feet, with
marine layer clouds not expected to reach the fire location
overnight.

Red flag conditions observed today across portions of the Antelope
Valley, LA county mountains, and Santa Clarita Valley. Current Red
Flag Warnings for those areas are set to expire at 9 pm, which
looks on track as onshore winds will continue to slowly diminish
tonight. Despite the diminishing winds, there will be poor
humidity recoveries tonight across the mountains and foothills.

Other area of concern is gusty sundowner winds this evening and
again Tuesday evening across the portions of the Santa Ynez
mountains and SBA south coast, especially from Gaviota to Goleta.
As of 8 pm, SBA-SMX gradient was at -4.4 mb. With not much in the
way of upper level wind support, looking for localized wind gusts
in the 35 to 40 mph range. These winds coupled with warm/dry
conditions will bring elevated fire danger over that area this
evening and again Tuesday evening. As of 8 pm, Montecito Hills
reporting north winds gusting to 26 mph with a temperature of 90
degrees and humidity of 10 percent.

Fire weather conditions improve a bit Tuesday all areas with the
upper level ridge beginning to weaken, bringing cooler
temperatures and slightly higher minimum relative humidities. The
single digit relative humidities will be restricted to far eastern
Antelope Valley, although min RH`s in the lower teens will
reappear across all interior sections. Winds, however, will not
be as strong as today`s, but still breezy in spots in the
afternoon to warrant elevated fire weather conditions.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...Small Craft Advisory in effect from 3 PM Tuesday to 3 AM PDT
      Wednesday for zone 645. (See LAXMWWLOX).
     Small Craft Advisory in effect until 3 AM PDT Wednesday for
      zones 650-670-673-676. (See LAXMWWLOX).
     Small Craft Advisory in effect until 3 AM PDT Tuesday for
      zone 655. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK...(THU-MON)
No significant hazards expected.

&&

$$

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

weather.gov/losangeles


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