Scientific Forecaster Discussion
fxus66 klox 231020
Area forecast discussion
National Weather Service Los Angeles/Oxnard California
320 am PDT Fri Jun 23 2017
high pressure aloft centered over southern Arizona will continue
to bring very warm conditions away from the coast into next week.
Skies should be fair, except for night through morning low clouds
and fog. A cooling trend should develop Tuesday as a low pressure
system off the California coast will weaken the upper- level dome
of high pressure and increase onshore flow.
Marine layer is up to 2000 feet and the onshore flow is 2 mb
stronger to the east and 1 mb stronger to the north. This has
allowed marine layer stratus to move into all of vlys including
the Santa Clarita. The lifting of the marine layer has created
some drizzle and also removed the dense fog. The deep marine layer
will also bring more cooling into the vlys and lower elevations of
the mtns as well. The stronger onshore flow will mean the low
clouds will clear slowly and will likely not clear at all for most
of the beaches. No change to the inland temps where much above
average hgts will keep the much above normal temps going with
little change from ydy.
A little north flow will set up tonight although it will be weaker
than previously thought as the central Vly high pressure does not
really show up. There will be sub advisory north winds through the
I-5 corridor and the sba South Coast. This north push will limit
The Vly penetration of the low clouds and will keep the western
half of the sba South Coast clear.
Weaker pressure gradients will allow for slight faster/better
clearing on Saturday. This will create some warming across the
coasts and vlys. The inland areas will see little change in the
relentlessly hot temps. The atmosphere over the mtns will become
pretty unstable but there is no low level moisture to work with.
There is some mid level moisture and there will likely be some
altocumulus castellanus clouds in the afternoon.
The ridge pushes slowly to the east on Sunday but not really fast
enough to influence the temps. In fact the day will be very
similar to Saturday except that the mtns will be more stable and
thus there will be no afternoon clouds.
GFS and ec agree through Tuesday. Both mdls flatten the ridge as
well as pushing it southward hgts fall from 593 dm to 590 dm
Monday and to 588 dm Tuesday. Onshore flow increase to the east
but decreases and actually turns offshore Tuesday. So there will
be a general cooling trend esp inland through the period with the
exception of few Vly location below north oriented canyons. Buy
Tuesday Max temps will approach or reach normal at most locations.
The Wed and Thu forecasts are still in doubt as ec and GFS
continue to exhibit different forecasts. The ec begins to build a
ridge into the area while the GFS continues with the troffing
scenario. Both mdls have hung on to their respective fcsts for a
couple of days now it will be interesting to see which one blinks
and trends to the other's solution (hopefully it will not be the
annoying situation where both mdls change and adopt the others
forecast) for now have coordinated with the surrounding offices
and have agreed to persist with the cooler GFS soln.
At 0930z at klax, the marine layer depth was near 2200 feet. The
top of the inversion was around 5000 feet with a temperature near
26 degrees celsius.
For 12z tafs...moderate confidence in respect to stratus
persisting across coastal tafs much of today. Lower confidence in
timing of LIFR-IFR cigs going up a category this morning. Higher
confidence for MVFR cigs for areas S of Point Conception after 16z
this morning. 30% chance no clearing will occur today for klgb,
klax, koxr before 22z. For terminals that have LIFR conds north of
Point Conception, 30 percent chc that conds will remain IFR.
Terminals that are forecast to have no clearing may see some sct
conds 22z- 01z.
Klax...moderate confidence in taf. There is a 30 percent chc of no
afternoon clearing. Very high confidence that there will not be an
east wind component over 5kt.
Kbur...moderate confidence in taf. There is a 40 percent chc that
MVFR cigs will not scour out until 20z.
Winds will remain below Small Craft Advisory levels through
Friday night across the outer waters, then gradually increase
through Monday. There is a 50 percent chance of Small Craft
Advisory level winds developing Saturday morning with a better
chance by the afternoon. Across the outer coastal waters but more
likely Saturday and through the weekend. Across the inner waters,
confidence is high there will not be any Small Craft Advisory through the weekend.
However there will be a 50-60% chance for local gusts to 25 kt
across the northwest portion of the sba inner waters.
A 2-3 foot south swell at 16-17 second period will last through
Saturday and may pose a risk for breaking waves nearshore. People
boating or kayaking near shore should use extra caution.
Although the coverage of dense fog is easing a bit, there is still
a 40% chance of patchy dense fog during the night and mornings
through the weekend.
California...heat advisory in effect until 9 PM PDT Sunday for zones
38-52-53. (See laxnpwlox).
Beach hazards statement in effect through Saturday evening
for zones 40-41-87. (See laxcfwlox).
Excessive heat warning in effect until 9 PM PDT Sunday for
zones 54-59. (See laxnpwlox).
Hazard potential outlook...(sun-thu)
hot temperatures with potential heat impacts will continue for
inland areas Sunday.