Area Forecast Discussion
Issued by NWS Los Angeles, CA

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000
FXUS66 KLOX 281014
AFDLOX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
314 AM PDT WED SEP 28 2016

.SYNOPSIS...

A weak area of low pressure will bring a slight chance of afternoon
showers and thunderstorms to the mountains and adjacent valleys of
Ventura and Los Angeles Counties on Wednesday. By Friday, a broad
upper level trough of low pressure will arrive to increase the
marine layer and cool temperatures to near normal through the
weekend and into early next week.

&&

.SHORT TERM...(TDY-FRI)

An interesting day today. A 579 DM upper low is moving out of
Mexico. At the sfc a large east pac high is moving in and
drastically decreasing the offshore flow...in fact...the KBFL
graduand is a MB onshore at the moment. There is a sheet of
stratus moving down the central coast and some mid clouds rotating
into and over LA and VTA county. By dawn there will be some low
clouds over the immediate central coast. The good news is that
max temps will be down 5 to 10 degrees today...the bad news is
that dew points are trending higher as the low pushes some sub
tropical moisture up and over the area. So the cooling will not be
as noticeable as it could be. There may be a little more cooling
than forecast over LA and VTA counties if the mid and high clouds
are thicker and/or more extensive than forecast. Although the
mdls have backed off a little on the convection for this
afternoon...it still looks like it could be an interesting
afternoon. Moisture and some weak PVA will advect around the low
over the AV and into the mtns of LA and VTA counties. LIs drop to
-4 and current forecast of chc TSTMs over the higher peaks and
slight chc of the rest of the mtns. The NE flow could steer any
TSTMs that do form into the LA/VTA vlys so a slight chc of TSTMs
there seems like the right call.
ea of low pressure will bring a slight chance of
afternoon showers and thunderstorms to the mountains and adjacent
valleys of Ventura and Los Angeles Counties on Wednesday. By Friday, a broad upper level trough of low pressure will arrive to
increase the marine layer and cool temperatures to near normal
through the weekend and into early next week.
The gradients will be onshore tonight but it does not look like
the marine inversion will be very organized south of Point
Conception so the marine stratus will be confined to the Central
Coast. The upper does not move out very quickly and there is non
zero chc of enough residual moisture hanging around for some
convection over the eastern San Gabriels but at this time it does
not seem likely enough to mention. Max temps will cool a little
more.

An upper trof will approach from the NW on Friday. But it does
not look like it will arrive quickly enough to really influence
the weather. Otherwise hgts and grads look very similar to
Thursday and Friday should be about the same...maybe a degree
cooler.

.LONG TERM...(SAT-TUE)

A Pac NW upper low will slowly approach and move into Oregon over
the weekend. Hgts will slowly lower through the period and the
onshore flow will steadily increase. This along with the cyclonic
turning will increase the marine layer each day and by Sunday both
the coasts and the vlys will be covered with morning Stratus. Max
temps will cool to around normal Saturday and then to a few
degrees blo normal Sunday.

Both the EC and GFS agree that a dry cold front will push through
the area on Monday. The mdls do not agree exactly on timing or
intensity of the upper low and trof...but for now the exact
details are not necessary. Aside from the coastal and vly morning
low clouds...There should be enough clouds to call the day partly
cloudy. Max temps will be on the cool side 4 to 8 degrees blo
normal.

The cool air behind the front will mix out the marine layer and
Tuesday will be partly cloudy at worst. It will likely be a
fairly breezy day. The cool air advection will not allow for any
warming and max temps will be similar to Monday`s.

&&

.AVIATION...

27/2350Z...

At 2304Z...the marine inversion at KLAX was 600 FT deep. The top of
the inversion was at 1400 ft with a temp of 27 deg C.

Generally hi confidence in the 00Z TAFs. There is a 60-70 percent
chance of low clouds and LIFR conditions at KSBP and KSMX from about
10Z-18Z, altho the timing of the onset of the low clouds may be off
+/- an hour or so. Otherwise, VFR conditions can be expected at all
airfields thru Wed afternoon.

KLAX...Hi confidence in the 00Z TAF with VFR conditions expected
thru Wed evening.

KBUR...Hi confidence in the 00Z TAF with VFR conditions expected
thru Wed afternoon.

&&

.MARINE...

27/835 PM...

Mostly light winds are expected across the coastal waters through
Thu afternoon with SCA conds not expected. Northwest winds are
expected to increase across the outer waters and northern inner
waters late Thu, with SCA conditions likely in those areas
by Fri evening and continuing through at least Sun. There is a 30
percent chance that SCA spread into the SBA Channel by Sat with a
50 percent chance Sun, with a 20 percent chance of SCA conds
across the southern inner waters by Sun. There is a 20 percent
chance of Gale Warning conditions sometime this weekend mainly
across the outer waters from Point Conception to San Nicolas
Island.

Extra surging and currents are possible near the coast due to a
long period south swell of 2 to possibly 4 feet by Thursday
morning, peaking late in the day into Friday before subsiding this
weekend.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...NONE.

&&

$$

PUBLIC...Rorke
AVIATION...DB
MARINE...DB
SYNOPSIS...Seto

weather.gov/losangeles


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