Area Forecast Discussion
Issued by NWS San Diego, CA

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FXUS66 KSGX 222040
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
140 PM PDT Fri Sep 22 2017

.SYNOPSIS...
A low pressure trough covering the West will continue the cool
weather through Saturday. The trough will weaken early next week,
allowing offshore flow to develop, bringing much warmer and drier
days, and clear, cool nights. Northeast winds could get gusty at
times below offshore wind-prone passes and canyons at times.
Autumn officially began this afternoon at 102 PM.

&&

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

Partly cloudy skies continue west of the mountains under a weak
marine inversion that has allowed shallow convection. Expect
similar partly cloudy skies through at least Saturday morning.
The atmosphere jumped the sun by bringing cool fall weather a day
early yesterday. That came courtesy of a big and unseasonable
trough of low pressure over the West. But wait, now that it`s
fall since 102 pm, it has become a big early season trough. Bring
in the cats and close those windows the next couple nights; we`ll
be dropping into the 50s for most areas. The big trough will take
its sweet time to move east because recent model runs keep
showing shortwaves dropping down the west side of the trough. The
northerly flow on the west side of the trough along with offshore
pressure gradients will get the offshore flow going on schedule
Sunday. That will sweep all clouds away and crank up some
northeast winds. The strongest winds will appear in foothills and
locally into valleys, primarily in and below the Cajon Pass.
That`s because the offshore pressure gradient from Nevada is
northerly, so San Diego County will not be in a favorable position
for strong winds. Monday and Tuesday look like the strongest wind
days overall, although offshore flow will continue all week.
Temperatures will slowly and gradually rise a couple degrees each
day as high pressure aloft slowly and gradually builds. Then
comes the uncertainty as some model guidance features a weak cut
off low to settle over the Southwest around the middle of next
week. That will keep the offshore flow going, but may dampen the
warming trend. As we see it now, it will warm up into the 90s for
some areas the latter half of next week. But the hotter days will
be tempered by the dry northerly flow and cool nights.

&&

.AVIATION...
222030Z...Coast/Valleys/Coastal Slopes...VFR will continue to
prevail today with FEW-SCT040-050 with just a few BKN patches. More
stratus with bases mostly 2500-3500 ft will develop after 23/04Z and
persist through mid-late morning on Saturday with clearing during
the day occurring.

Mountains/Deserts...Clear with unrestricted visibility through
Saturday afternoon.

&&

.MARINE...
Northwest winds near 20 KT will be accompanied by combined seas of 5-
8 ft and steep waves, resulting in hazardous boating conditions. The
Small Craft Advisory continues through 1 AM Saturday. Lighter winds
and smaller seas are expected over the weekend.

&&

.FIRE WEATHER...
Offshore flow will develop Sunday, dropping RH considerably, and
periods of gusty northeast winds are likely along the coastal
slopes and foothills, peaking through and below favored passes and
canyons of San Bernardino, Riverside, and Orange Counties
Mon/Tue. At this time, it looks like local winds of 25 to 35 mph
with isolated gusts topping 40 mph, especially Mon/Tue mornings.
Several hours of near critical fire weather conditions are
possible in these foothills areas, mainly north of San Diego
County Mon/Tue as RH falls to 10-15% and winds exceed 25 mph.

&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...

CA...NONE.
PZ...Small Craft Advisory until 1 AM PDT Saturday for Waters from San
     Mateo point to the Mexican Border Extending 30 to 60 nm out
     including San Clemente Island.

&&

$$

PUBLIC/FIRE...MM
AVIATION/MARINE...Gregoria



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