Area Forecast Discussion
Issued by NWS Los Angeles, CA
FXUS66 KLOX 060106
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
506 PM PST Mon Dec 5 2016
The onshore flow will bring clouds...fog and patchy drizzle tonight.
Then a high and breezy offshore winds will bring a warming trend
through Thursday. A low system will bring possible precipitation
from late Thursday into the weekend for San Luis Obispo and Santa
Barbara counties and the Ventura mountains.
Water vapor imagery this afternoon is showing broad NW flow aloft,
which will set up some the next couple of nights. A weak upper-
level disturbance moving through the Great Basin will aid in the
development of locally gusty north winds in southern SBA County
and through the I-5 Corridor tonight, but winds should generally
remain below advisory level. A slightly stronger upper-level
trough will move through the Great Basin tomorrow, resulting in
better subsidence and better upper-level support. As a result,
there will be a better chance for advisory level winds tomorrow
evening for areas along and adjacent to the Santa Ynez Range and
the I-5 Corridor.
By Wednesday morning, surface high pressure building into the
Great Basin will result in a weak to possibly moderate Santa Ana
event. The latest NAM suggests a LAX-DAG gradient of about -4 to
-5 mb by Wednesday morning, however, upper-level support is not
that impressive. At this point, it looks like NE winds in Ventura
and LA County will stay just below advisory level on Wednesday.
Similar gradients are expected for Thursday morning, but the
upper-level support will be even weaker.
Aside from any wind issues and elevated fire danger associated
with the sundowner winds and Santa Ana winds, it looks like low
clouds and fog could become more widespread across the LA and
Ventura coast/valleys late tonight and Tuesday morning. The
latest LAX AMDAR sounding shows a marine layer depth of about 2400
ft. The marine layer depth should come down to around 1000 ft this
evening, but will deepen again overnight as a coastal eddy
develops in response to stronger NW winds across the outer
coastal waters. There could even be some patchy drizzle as the
marine layer deepens. Offshore flow on the Central Coast should
keep stratus out of areas north of Pt. Conception, while sundowner
winds will likely prevent it from reach the SBA south coast.
Probably won`t have any stratus issues for Tuesday night and
Wednesday morning as the offshore flow develops across Ventura and
Tomorrow will likely be the coolest day of the week. Slight
warming is expected on Wednesday as offshore flow develops, but
temperatures will still generally be slightly below normal.
South of Pt. Conception, temperatures will warm to near normal on
Thursday as weak offshore flow continues in the morning and
height/thickness values rise with the upper-level flow becoming
Areas north of Pt. Conception could see an increase in clouds and
a 20-30% of rain on Thursday as a frontal system sags southward.
Best chance of rain on Thursday will be in northern SLO County.
Friday through Sunday could be rather unsettled north of Pt.
Conception, as a frontal system stalls out to the north. There`s
a good chance areas north of Pt. Conception (especially SLO
County) will see some rain during this period, but PoPs in the
forecast are only 20-40% at this point as there could be multiple
weak disturbances and timing is uncertain. The latest ECMWF
actually swings a weak front through Ventura and LA County
Saturday night into Sunday, but not confident enough to include
rain in the forecast at this point. Rain chances will likely
diminish by Monday.
We`ll also have to keep an eye on the possibility of some
northerly winds developing again over the weekend as the weak
disturbances move through the region. Temperatures are generally
expected to remain near normal, with highs in the 60s to near 70.
At 00Z, the marine layer was around 1400 feet deep at KLAX. The
top of the inversion was near 3700 feet with a temperature of 13
North of Point Conception...VFR conditions are expected throughout
the period except for a chance of sub-VFR conditions after 06Z
at interior valley terminals.
South of Point Conception...IFR to MVFR conditions will become
prevalent through 14Z. There is a chance of LIFR conditions
through 14Z, especially for valley terminals. MVFR conditions
should linger through at least 18Z with a chance of hanging around
into Tuesday afternoon.
KLAX...IFR to MVFR conditions will become prevalent between 01Z
and 04Z. There is a 30 percent chance of LIFR conditions between
04Z and 14Z. MVFR conditions should linger until between 18Z and
22Z. Any east winds should remain less than 7 knots.
KBUR...LIFR to IFR conditions will spread in between 06Z and 10Z,
then likely improve one category between 10Z and 14Z. MVFR
conditions should linger until between 17Z and 20Z.
Outer Waters...High confidence in SCA winds lasting through early
Wednesday. The SCA winds will likely continue into Wednesday in
zones 673 and 676. There will be local Gale Force gusts during
the afternoon and evening hours through Tuesday.
Inner Waters...Good confidence in Todays forecast. Fair
confidence in Tuesdays forecast with a 30 percent chc of SCA winds
across the western third of the area.
PZ...Small Craft Advisory in effect until 3 PM PST Wednesday for
zones 670-673-676. (See LAXMWWLOX).
.HAZARD POTENTIAL OUTLOOK...(THU-MON)
No significant hazards expected.