Area Forecast Discussion
Issued by NWS Los Angeles, CA

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FXUS66 KLOX 240622

1122 PM PDT Wed Aug 23 2017

New Aviation Discussion

Mostly clear skies into next week, except for an overnight
coastal marine layer. The temperatures will be around normal into
Thursday. Then the temperatures will soar to well above normal
from Saturday into next week as a high moves in.



Weak upper level low pressure system will move over the
forecast area tonight. This system has fired off some
convective thunderstorms this evening to our east
across the San Bernardino County deserts. For our
area, just some cumulus buildups over the local
mountains along with the return of marine layer clouds
across coastal areas this evening. The marine layer
depth will remain around 2000 feet tonight, so looking for
marine layer clouds to fill in across most of the valleys
overnight into Thursday morning. Will also see some locally gusty
northwest winds tonight across the western portions of the Santa
Ynez mountains and I-5 corridor.

Slight warming expected across interior sections on
Thursday then bigger increase by Friday as heights and boundary
layer temperatures increase. Expecting to see most valley areas
climb well into the 90s on Friday, with the Antelope Valley
expected to see a return of 100 degree readings. By Friday
morning, also expecting to see marine layer clouds mostly confined
to the coastal plain. As upper level ridge strengthens over the
area on Saturday, looking for the beginning of a long duration
heat wave to begin. On Saturday, expecting 100 degree readings to
spread to some of the warmest valley and lower mountain locations.
Special Weather Statement issued to highlight potential for
significant heat impacts and elevated fire danger this weekend
into the middle of next week, and possibly longer.


A significant warming trend is becoming more likely for Sunday
through Wednesday. Model solutions are impressive warming 950 mb
temperatures up to 35-40 degrees Celsius across the area for an
extended period beneath a 594 dm heights. Forecast temperatures
are on the cool side of local temperatures studies for the region,
but if model parameters verify as progged currently, valleys,
foothill, and desert afternoon high temperatures warming into the
100-110 degree range could come into play. An excessive heat watch
may be needed over the coming days, if this pattern continues to
remain consistent.

While the forecast maintains a dry stance for early next week, the
ridge position would be consistent with the possibility of a
window opening for monsoonal flow to enter at some point. Have
added in some clouds to the Ventura and Los Angeles County
mountains and have raised probabilities of precipitation but not
so high as a slight chance so far. Focusing on the heat wave for



At 0530Z, the marine inversion at KLAX was based at 1700 feet.
The top of the inversion was 2800 feet with a temperature of 20
degrees Celsius.

Moderate confidence in category of low cigs vsbys. There is a 30
percent chance of low MVFR cigs vsbys at KBUR, KVNY, and KOXR
after 09Z. Low confidence in timing clearing low cigs/vsbys for
coastal TAF sites with moderate confidence for valley locations.
Low confidence in return of low cigs/vsbys with timing off by up
to 3 hours, locally more. There is a 20 percent chance of low
cigs/vsbys prevailing through the period for coastal areas from
KLGB to KOXR including KLAX. There is nearly an equal chance of
low MVFR to IFR cigs after 00Z/25 for coastal and valley TAF sites
south of Point Conception.

KLAX...Moderate confidence in TAF through 23Z/24. Low confidence
in timing of the return of low cigs/vsbys (could be off by three
hours with nearly equal chance of low MVFR and IFR flight
category. There is a 20 percent chance that low cigs/vsbys prevail
through the TAF period.

KBUR...Moderate confidence in TAF. There is a 30 percent chance
of low MVFR cigs/vsbys mainly after 09Z.


.MARINE...23/800 PM...

For the Outer Waters, moderate to high confidence in current
forecast. Northwest winds over the outer waters have increased
more quickly than previously thought...with SCA gusts over the
southern zones and expected to increase by midnight over PZZ-670.
The gusty winds are likely to persist through Saturday. On
Sunday, winds should diminish below SCA levels.

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 tonight. On Thursday and Friday, northwest
winds will increase with SCA level winds likely each afternoon and
evening. For Saturday and Sunday, winds are expected to drop
below SCA levels. For the waters south of Point Conception, winds
and seas will remain below SCA levels through Sunday.


PZ...Small Craft Advisory in effect until 3 AM PDT Friday for
      zones 670-673-676. (See LAXMWWLOX).


A heatwave will likely develop this weekend and extent through the
middle of next week.



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