Scientific Forecaster Discussion
fxus66 klox 121129
Area forecast discussion
National Weather Service Los Angeles/Oxnard California
329 am PST Tue Nov 12 2019
It will be sunny today except for morning low clouds along the
coasts and locally into the valleys. It will be cloudy and cooler
during the mid week period. Skies will be clear with warmer
temperatures for Friday and the weekend.
Short term (tdy-thu)...12/329 am.
The marine layer is about 1200 ft deep over la County and about
half that amount across the central coast. Gradients are near
neutral and this along with the lack of an eddy has greatly slowed
the inland progress of the low clouds. The marine layer is shallow
enough across the central coast to create plenty of dense fog. A
dense fog advisory is in effect for the central coast through 900
am. The forecast offshore wind event really is not panning out due
to the weaker than forecast gradients. There will be local 15 to
25 mph winds this morning but thats about it. The inversion is
pretty steep above the marine layer and this will hinder clearing
this morning. Some central coast beaches may remain cloudy all
day. 585 dm hgts courtesy of a east pac ridge nosing in from the
west along with a weaker than normal sea breeze will allow for Max
temps to bump up a few degrees esp inland. The marine layer,
however, may cool some of the beaches.
A slightly unusual pattern sets up for Wed and Thu as trof moving
in from the northwest tips the ridge over to the east allowing SW flow
to establish itself over the state. The SW flow will tap into a
grip of mid and high level subtropical moisture and skies will
likely be mostly cloudy through the period. There may be some
night through morning low clouds as well but the abundance of high
level moisture will likely inhibit their formation. There will be
3 to 6 degree of cooling each day and Thursday will be the coolest
day for the coast and vlys of the next 7 with Max temps 2 to 5
degrees blo normal.
Long term (fri-mon)...12/328 am.
A weak trough will ripple through southwest California on
Friday. This will cut off the mid and high level clouds and skies
will clear...except for a coastal marine layer stratus deck that
will likely form with weak lift from the trof and the onshore
trends. The increased sunshine will balance out the lower hgts
across the coasts and vlys and temps will not change much except a
little offshore push from kbfl may bring a few degrees of warming
to the central coast. The cooler air advected in by the trof will
bring another 3 to 6 degrees of cooling to the interior which
will have its coolest day of the week.
Another ridge builds in Friday night and offshore flow will
develop. There should be enough of an offshore push to eliminate
the marine layer but not enough to bring much in the way of canyon
winds. Most areas will see about 6 degrees of warming due to
higher hgts and the offshore push.
Better offshore flow on Sunday and also a little upper support for
a Santa Ana. Ec as has been the case all fall is stronger and if
it verifies there will likely be some advisory level gusts in the
morning in the usual places across la/vta counties. Along with the
winds will come warming and drying with the usual fire weather
concerns. There will be another 3 to 6 degrees of warming and
almost all of the coasts and vlys will see highs in the 80s.
Both the ec and the GFS weaken both the ridge and the offshore
flow on Monday. Still enough offshore flow to keep the low clouds
away. But there will be several degrees of cooling across the
Ec and many of its ensemble members and to a lesser degree the GFS
and a few of its ensemble members show some rain developing on
Thursday the 21st. Not a guarantee but something to watch.
At 2230z at klax, the marine layer was 1000 feet deep. The top of
the inversion was at 1800 feet with a temperature of 22 c.
Low confidence in all coastal and Vly tafs through 18z due to
uncertainty in timing, cig hgt and vis. There is a 40 percent chc
of LIFR cigs at ksbp 10z-16z and a 40 percent chc of no cigs at
kbur and kvny. Good confidence in tafs after 18z.
Klax...low to moderate confidence in taf. There is a 30% chance
that cigs will remain between 006 and 008. There is a 30 percent
chc of 6sm haze sct010 conds at 17z. Good confidence that any east
wind component will be 5 kt or less. Low clouds could return as
early as 04z Tuesday evening.
Kbur...low confidence in taf through 18z then high confidence.
There is a 40% chance that skies will remain clear thru the pd.
For all of the coastal waters, high confidence that winds and
seas will remain below Small Craft Advisory (sca) level through
Thursday. Moderate confidence that Small Craft Advisory level winds may impact the
offshore waters along the central coast and southward towards San
Nicolas Island on Friday and Saturday.
Patchy dense fog with visibility of one nautical mile may impact
all of the coastal waters this morning.
A large and long period northwest swell is likely to impact the coastal
waters Friday into the weekend, but low confidence on timing and
California...dense fog advisory in effect until 9 am PST this morning for
zones 34-35. (See laxnpwlox).
Hazard potential outlook (thu-mon).
There is the potential for moderate Santa Ana winds next Sunday
with elevated to critical fire weather conditions possible.