Area Forecast Discussion
Issued by NWS Los Angeles, CA
FXUS66 KLOX 301637
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
937 AM PDT FRI SEP 30 2016
A trough of low pressure dropping south from British Columbia
will bring cool conditions to the region Saturday through Monday
with night to morning low clouds spreading into the valleys. As
the trough departs to the east by the middle of next week, locally
gusty northwest winds are expected to transition offshore,
supporting a return to warm and dry conditions.
Similar day today as yesterday in most areas with temps on average
1-3 degrees cooler. A strengthening nw-se pressure gradient will
increase winds over the coastal waters around Pt Conception today
and also later this afternoon and evening along the Central Coast
and southern SB County. 12z NAM shows the SBA-SMX gradient peaking
around -3.7mb which is pretty strong, but model cross sections
through the Santa Ynez range show limited upper level support, so
this is mostly a gradient driven event. Given the gradient I
expect we`ll see at least some brief advisory level gusts,
especially up in the foothills west of Goleta, but will hold off
issuing an advisory for now as see how things develop this
***From previous discussion***
An upper low off the Oregon coast with open up and move into the
Pac NW later today and tonight, with its associated trough
extending southward will push into the West Coast. The WRF
shows an eddy circulation developing tonight, and indicates low
clouds pushing into coastal sections of L.A. County, the Central
Coast and Santa Ynez Valley. There is a chance that some stratus
will push into the San Gabriel Valley by early Sat morning as the
marine layer begins to deepen.
Across SBA County, increasing N-S gradients will likely bring
some gusty winds to the Santa Ynez Mountains and to the south
coast of SBA County through and below passes and canyons tonight.
At this point, expect winds to remain below advisory levels.
More significant cooling is expected across the region on Sat,
with max temps down to near normal levels in most areas.
Another upper low will drop into a position off the Oregon coast
by early Sunday morning, with a trough extending southward off
the CA coast. Expect the marine layer to deepen, with night
through morning low clouds and fog in most coastal and valley
areas Sat night/Sunday morning. Decent N-S gradients should bring
another round of gusty winds to southern SBA County Sat night,
and will likely keep skies clear there.
The upper trough will swing across northern CA and into Nevada
Sunday and Sunday night. Strong west to northwest winds aloft and
an area of decent subsidence spreading into the region behind the
trough axis should bring gusty winds to portions of the region
Sunday afternoon into Sunday night. Winds will be gusty on the
Central Coast, across the Antelope Valley, through the Interstate
5 corridor, and through and below passes and canyons of the Santa
Ynez Range into the south coast of SBA County. This looks as
though it may be a decent wind event, with gusts to 50 mph
possible in some areas. Wind Advisories will likely be needed in
some areas. Expect even more significant cooling across the
region on Sunday. Max temps should be at least a few degrees below
normal just about everywhere. The exception may be across the
south coast of SBA County due to the nly flow.
A weakening inversion due to cooling aloft will likely affect the
marine layer Sun night, so expect low clouds to be more patchy in
nature, especially across SLO and SBA counties where skies could
remain clear. Max temps could be down a bit more on Monday,
especially in the mtns and deserts, with highs well below normal
in most areas. The upper trough will move eastward Tue and Wed
and an upper high will build into the region. Weak offshore flow
should keep skies clear. There will a significant warming trend
Tue and Wed, with temps back to above normal levels by Wed, then
similar temps are expected on Thu.
At 1015Z, the marine inversion at KLAX was based near 500 feet.
The top of the inversion was 1800 feet with a temperature of 25
Overall, moderate to high confidence in 12Z TAF package. This
morning, expect only the Central Coast to experience any CIG or
VSBY restrictions with widespread LIFR/VLIFR conditions which
should dissipate by late morning. Moderate confidence in areas
south of Point Conception remaining VFR through this evening (20%
chance of IFR/LIFR conditions developing 12Z-17Z at coastal TAF
sites). For tonight, IFR/LIFR conditions should return to the
Central Coast and some IFR conditions are expected to develop
across the LAX coastal plain.
KLAX...moderate confidence in 12Z TAF. High confidence in VFR
conditions through this evening (10% chance of IFR conditions
12Z-17Z). For tonight, moderate confidence in return of IFR
conditions, but low confidence in timing.
KBUR...high confidence in 12Z TAF. VFR conditions will prevail
through the period.
Areas of dense fog north and west of San Miguel Island will
dissipate by late this morning. Otherwise northwest wind will
increase and small craft advisory conditions will exist from
Piedras Blancas to San Nicolas Island Friday afternoon through
next week Monday with gale force gusts each afternoon Saturday
through Monday. Northwest winds will likely fill in over the inner
basins each afternoon Saturday through Monday.
Sundowners expected the next few nights for canyons and passes
below the Santa Ynez Range along the Santa Barbara County south
coast. Gusty northwest winds to about 35 mph will occur west of
Goleta tonight then will be more widely felt and peak near the
foothills from Montecito to Goleta by Sunday night when gusts
could be near 50 mph.
A cold low pressure system will move across northern California on
Sunday then eastward to the Great Basin by Monday. Much stronger
west-northwest winds will bring gusty conditions to all areas
Sunday afternoon with gusts to 35 mph for valleys and coasts, and
to 55 mph in the mountains and deserts. Relative humidities will
fall to single digits at ridgetop level on Sunday bringing several
hours of critical fire weather to higher elevation sites, but
temperatures will be below normal. No fire weather watch is
expected at this time. Similar dry conditions will occur on
Monday with winds turning northwest-north and remaining quite
gusty for the Antelope Valley and the San Gabriel Mountains.
High pressure will start to build on Tuesday and Wednesday with
north winds diminishing and temperatures rebounding back near
normal by mid-week.
PZ...Small Craft Advisory in effect from 3 PM this afternoon to 9
PM PDT this evening For zone 645. (See LAXMWWLOX).
Small Craft Advisory in effect until 3 PM PDT Saturday For
zones 670-673-676. (See LAXMWWLOX).