FXUS66 KLOX 212053

153 PM PDT Mon Aug 21 2017

A weak trough of low pressure over the Channel Islands will
continue to keep a cooler than normal air mass in place through
midweek. Night and morning coastal low clouds will continue
through late week as the trough exits the region on Wednesday and
high pressure aloft builds in for late week. A significant warming
trend is possible for next weekend.



Marine lyr clouds have cleared most areas this afternoon and so
far no cumulus over the mountains. Given the sharp drop in
precipitable water across the area today and slightly less
instability this makes sense. Heights rise a bit tonight as the
upper low near Pt Conception weakens. This should allow for some
lowering of the marine lyr depth but not enough to keep it out of
most valley areas yet. Still, between the lower marine lyr and
another night of 1-2mb offshore trends most areas should see a few
degrees of warming Tuesday, especially the valleys.

A slight onshore trend Wednesday and Thursday may bring a degree
or two of cooling to coast and coastal valleys Wednesday but
otherwise very little change. Low clouds will continue to push
into the valleys overnight and clear to around the coast or just
offshore during the afternoon. Monsoon moisture will remain well
to the east so no convection expected.


Friday will be the beginning of what appears to be a significant
warming trend that will last at least through the middle of next
week. Friday and Saturday will just be a couple degrees warmer
with still some decent onshore flow in place and low clouds
likely still reaching the coastal valleys overnight. By Sunday,
however, high pressure is expected to strengthen from the
southeast and onshore flow will be weakening quite a bit. Highs
expected to reach the triple digits in the warmer valleys Sunday
and even warmer Monday. And by next Tue or Wed we could be looking
at some weak offshore flow in the morning and highs into the 90s
for some coastal areas and well over 100 for the valleys. The door
is open for monsoon moisture but models still not showing
anything moving into our area at least through early next week.



At 1800Z, the marine inversion at KLAX was based at 2500 feet.
The top of the inversion was 3800 feet with a temperature of 20
degrees Celsius.

Moderate confidence in 18Z TAF package mainly due to a persistence
forecast. MVFR conditions across most central coast and valley
terminals with low clouds clearing off the coast south of OXR.
CIGS are likely to dissipate from central coast sites after 20Z,
but reform to MVFR conditions 02-04Z this evening.

KLAX...moderate confidence in 18Z TAF. MVFR CIGs likely to reform
after 05Z and persist through 18Z Tue.

KBUR...moderate confidence in 18Z TAF. MVFR CIGs likely with a 40%
chance of IFR CIGS after 07Z, lingering through 17Z Tue.


.MARINE...21/100 PM...

For the Outer Waters, moderate confidence in current forecast.
Through Wednesday, winds and seas will remain below Small Craft
Advisory (SCA) levels. For Wednesday night, there is a 60 percent
chance of SCA level winds developing. For Thursday and Friday, the
winds will likely remain at SCA level and northwest to west swell
will build to 6-7 ft.
For the Inner Waters, high confidence in current forecast. For the
waters north of Point Sal, winds and seas will remain below SCA
levels through Wednesday. From Wednesday night through Friday,
SCA level winds will be possible mainly in the afternoon and
evening. For the waters south of Point Conception, winds and seas
will remain below SCA levels.




A significant heatwave could develop this upcoming weekend and
continue into early next week.




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