Area Forecast Discussion
Issued by NWS San Diego, CA

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FXUS66 KSGX 242120
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
220 PM PDT Sun Sep 24 2017

.SYNOPSIS... High pressure over the Great Basin will force weak to
moderate offshore flow over Southern California for most of the
week. The dry northeast winds will lower humidity, and bring
much warmer days and continued cool nights. Winds will be gusty
at times along the coastal foothills, and will increase the threat
of extreme fire behavior, especially from now through the middle
of the week.

&&

.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...

Offshore winds have kicked in today for locations along and west
of the coastal slopes. Winds have not been particularly strong but
the VWPs have been showing some isolated 25 knot measurements
just off the deck. these winds are bringing very dry and much
warmer conditions to the valleys with temperatures about 10
degrees above yesterdays readings, and dewpoints as much as 20 to
30 degrees lower. With the offshore flow as expected skies are
completely clear.

The offshore winds will increase tonight into Monday morning with
diurnal drainage and will pick up through the canyons and along
the coastal slopes, however we are not expecting these winds to
reach advisory levels except in isolated and remote locations as
is common during a moderate offshore regime. The pattern will
continue through Wednesday and then we will see some relaxing in
the offshore gradients due to a brief cutoff low developing in the
bottom of the trough over SE CA and W AZ with some marine layer
and sea breeze action each day over the coastal strip and into the
western valleys.

By next weekend, a broad high pres ridge may settle over SoCal
bringing another warmup with temperatures several degrees above
normal for all areas and no rain in site.

&&

.AVIATION...
242030Z...Clear skies and unrestricted vis will continue through
Monday. Local gusty northeast winds will occur through and below
passes and along the coastal slopes, with peak gusts 25-30 knots
this afternoon, increasing to 35-45 knots late tonight and Monday.
This will produce weak to moderate up/downdrafts and LLWS over and
southwest of the mtns. LLWS will most likely impact KONT as NE winds
will only occasionally reach the surface at that airport tonight
through Monday despite higher winds 1500-2000 ft above the surface.

&&

.MARINE...
No hazardous marine weather is expected through Friday.

&&

.FIRE WEATHER...
Offshore flow has developed this morning, and will become gusty
below the coastal slopes, canyons and passes of San Bernardino,
Riverside, and Orange Counties Mon/Tue. The RH will drop
considerably today, with minimum daytime values as low as 10% by
Monday. In the favored, offshore wind-prone areas, we are still
expecting to see occasional winds of 25 to 35 mph with isolated
gusts to 40 to 45 mph, especially Mon/Tue mornings. Several hours
of near critical fire weather conditions are possible in these
foothills areas, canyons, and passes, mainly north of San Diego
County Mon/Tue due to low RH and with winds exceeding 25 mph.
However, with the limited coverage and duration of critical
conditions, no fire weather product issuance is anticipated at
this time.

For the second half of the week, lighter winds are expected, with
a sea breeze each afternoon/evening. RH will show some modest
improvement, but it will remain very warm and dry through next
weekend.

&&

.SKYWARN...
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...NONE.
&&

$$

PUBLIC/FIRE WX...Brotherton
AVIATION/MARINE...Maxwell


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