Area Forecast Discussion
Issued by NWS Los Angeles, CA
FXUS66 KLOX 021156
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
456 AM PDT MON MAY 2 2016
There will be night through morning low clouds and fog today and
Wednesday with slightly above normal temperatures in the morning. A
slow moving low pressure system will bring a chance of showers
and thunderstorms along with cooler conditions to the area
Thursday through the weekend.
Low clouds are a little better organized this morning. The
gradients are about 3 MB onshore push both to the north and the
east and the marine layer inversion has strengthened both of which
are helping the marine layer stratus along. By dawn most of the
coasts and the vly will be covered with stratus. There will be
good clearing by the afternoon as there is no eddy and the onshore
push is not that strong. The barest of ridges pops up today and
this will allow for a little warming esp across the interior.
There is just enough residual moisture over the mtns to allow for
some afternoon cu but not enough lift or instability to form
Since the marine layer is already fairly well established the
stratus deck will reform a little quicker overnight. It will still
burn off pretty quickly. Skies will turn partly cloudy in the
afternoon as mid and esp high level clouds stream in the sw flow
ahead of an approaching trof. MDLs indicating quite a bit of
warming but with the ridge moving off and the increase of clouds
there will be...at best...only a degree or two of warming.
The trof will be right along the West Coast on Wednesday morning
and the lift associated with it will drive marine layer stratus
over the csts and vlys and onto the coastal slopes. Mid and high
level clouds will increase through the day. Onshore flow will
increase through the day as well. All of these trend will conspire
to cause a sharp drop in temperatures. Max temps will drop 5 to 10
degrees and will be 3 to 6 degrees below normal.
GFS/EC agree that a cutoff low pressure system will slowly drift over
the forecast area Thursday and Friday, then slowly move east over
the weekend. There will be a chance for hit and miss showers in
most places Thursday through Saturday (with the highest probability
from Thursday afternoon through Friday evening). The cold core
upper low (with 500 mb temperatures of -24 degrees Celsius) will
move across Southwest California sometime between Thursday
afternoon through Friday. The cold air aloft combined with early
May sunshine will be create enough instability to warrant a
slight chance of thunderstorms(especially over interior sections).
Right now it does not look like this system will have that much
moisture to work with and do not expect large rainfall amounts
with it. This system is cold enough that snow levels will likely
dip to between 5000 and 6000 feet.
AT 11Z, the marine layer depth at KLAX was around 1800 feet.
The top of the inversion was around 3000 feet with a temperature
of 15 degrees Celsius.
Widespread stratus on the Central Coast and in the Santa Ynez
Valley early this morning, with IFR to LIFR conds. Expect IFR to
LIFR conds to push into the Salinas Valley. South of Pt
Conception, stratus with IFR conds was affecting the south
coast of Sba County and the Vtu County coast, with IFR to LIFR
conds beginning to spread into the Vtu County valleys. Stratus
across Los Angeles county has been confined to southern sections,
but was beginning to spread northward, and will likely affect all
coastal sections of L.A. county by daybreak. Cigs were higher
here, with mostly MVFR conditions. Expect rather slow clearing,
especially in coastal sections of Vtu and southern Sba Counties,
where clearing may not take place until early afternoon.
Widespread stratus is expected in all coastal and valley areas
tonight, with IFR conds north of Pt Conception and MVFR conds
KLAX...Moderate confidence in the 12Z TAF. There is a 20 to 30
percent chance that cigs will not scatter out until at 21Z. There
is a 30 percent chance that cigs will not arrive tonight until
KBUR..Moderate confidence in the 12Z TAF. There is a 20 to 30
percent chance of low MVFR or high IFR cigs between 13Z and 17Z
this morning. There is a 20 percent chance that cigs will not
arrive tonight until after 12Z.
High confidence that SCA conditions will not affect the waters
through at least Tuesday afternoon. There is a chance that a
Small Craft Advisory may be needed across the outer waters
Tuesday night, with a better chance of SCA conds Wednesday.
Advisory level winds are likely across the outer waters by
CA...Beach Hazards Statement in effect until 10 AM PDT this
morning For zones 34-35-40-41-87. (See LAXCFWLOX).