Scientific Forecaster Discussion
fxus66 klox 231122
Area forecast discussion
National Weather Service Los Angeles/Oxnard California
422 am PDT Mon Apr 23 2018
There will be overnight and morning coastal low clouds and fog
for several days this coming week otherwise conditions will be
warm and dry. Temperatures will cool a bit Friday and Saturday as
a weak weather system moves across the region.
Short term (tdy-wed)...23/259 am.
Weak ridging along with onshore flow have combined to produce a
fairly widespread stratus deck this morning. Aircraft soundings
out of klax show the marine layer is 700 feet deep which is
shallow enough to keep the clouds out of all of the valleys except
for the lower portions of the San Gabriel Vly. It is also shallow
enough to create some dense fog which will last through mid
morning. The inversion is strong enough to prevent clearing at a
few beaches this afternoon. The stronger onshore flow will create
cooler temps across the coasts and to a lesser degree in the vlys.
Inland temps will change little.
Just a few little changes Tuesday. The ridge is a little weaker
so the marine layer will be a touch deeper and will extend a
little deeper into the vlys. Max temps will cool a little as well.
An upper low approaches northern California on Wednesday. It will push the
ridge a little more to the east. Hgts...though...really do not
change much. The lift from the trof should lift the low clouds
into the vlys. The inversion will be a little weaker and this will
allow the morning stratus to clear a little quicker. Max temps
will not change much from Tuesday and will be a few degrees above
Long term (thu-sun)...23/318 am.
Ec and GFS agree that the upper low will not move much on
Thursday. Things will be in pretty static pattern and like
Wednesday there will be a deep stratus pattern extending deep into
the vlys. Hgts and pressure grads do not change much and Max temps
will be similar to wednesday's.
The ec and GFS begin to disagree on the movement and evolution of
the low on Friday but the disagreement if more of a northern California
problem as there is not too much difference between the two mdls
for socal. Look for a troffier pattern with lower hgts. The deep
marine layer will continue but the lower hgts will usher in a
cooler trend and Max temps will fall to a degree or two blo
Very large disagreement for the forecast next weekend. The ec
brings a tight cut off 552 dm upper low over Sacramento while the
GFS has only a weak trof over the state. The ec seems a little
exuberant and based the weekend forecast on the GFS. Saturday
will be like Friday but by Sunday there should be enough cool air
mixing up north to prevent the stratus from forming across the
central coast. The cooler air will also bring Max temps down 2 to
4 degrees across the 4 County forecast area.
At 1035z, the marine inversion at klax was based around 900 feet.
The top of the inversion was 2700 feet with a temperature of
22 degrees celsius.
Overall, low confidence in coastal taf sites and high confidence
in inland taf sites. Currently, LIFR/vlifr conditions prevail at
coastal taf sites and these conditions should dissipate by late
morning. For tonight, high confidence in return of stratus to
coastal taf sites, but low confidence in timing and flight
category. For inland sites, high confidence in VFR through the
period (although there is a 20% chance of IFR/LIFR conditions
developing late at kbur/kvny)
Klax...low confidence in 12z taf. Conditions will bounce between
IFR and LIFR 12z-20z. Stratus could dissipate up to two hours
earlier than current 20z forecast. For tonight, high confidence in
return of stratus, but low confidence in timing (+/- 3 hours of
current 03z forecast) and flight category (50/50 chance of either
MVFR or IFR conditions).
Kbur...high confidence in 12z taf. There is a 20% chance of
IFR/LIFR conditions developing after 06z tonight.
For the outer waters, high confidence in current forecast. Winds
and seas will remain below Small Craft Advisory (sca) levels
through Wednesday. On Thursday and Friday, there is a 70% chance
of Small Craft Advisory level winds.
For the inner waters, high confidence in current forecast. For the
waters north of Point Sal, winds and seas will remain below Small Craft Advisory
levels through Wednesday. On Thursday and Friday, there is a 70%
chance of Small Craft Advisory level winds in the afternoon/evening hours. For the
waters south of Point Conception, winds and seas will remain below
Small Craft Advisory levels through Wednesday. On Thursday and Friday, there is a
60% chance of Small Craft Advisory level winds, especially across western sections.
Areas of dense fog will impact all the waters this morning with
Hazard potential outlook (wed-sun).
No significant hazards expected.