Area Forecast Discussion
Issued by NWS San Diego, CA

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000
FXUS66 KSGX 142052
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
152 PM PDT Sat Oct 14 2017

.SYNOPSIS...
High pressure aloft over Southern California will bring a warming
trend through Monday, when temperatures will be in the nineties
from near the coast to the mountains. Surface high pressure over
the Great Basin will bring periods of gusty northeast winds near
the coastal foothills and below passes and canyons...mostly
through Sunday morning. Weak onshore flow will return on Tuesday
and strengthen on Thursday and Friday. Slow cooling will begin on
Tuesday and Wednesday with greater cooling on Thursday and Friday
along with a chance of precipitation and periods of stronger and
gusty west winds for the mountains and deserts.

&&

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

Mostly clear this afternoon, except for a few high clouds. Sfc
pressure gradients are now -11.3 mb SAN-TPH, and the offshore
winds are surfacing in the I.E. So far today, the strongest gust
reported is 45 mph at Highland Springs last hour. Highland Springs
is at 2233 ft, a few miles south of Beaumont. The driest
conditions west of the mtns are in the northern I.E. where
relative humidities are less than 10 percent.

A ridge of high pressure aloft will strengthen over Southern
California into Monday with surface high pressure over the Great
Basin. This combination will bring a warming trend with very dry
conditions and periods of gusty northeast to east winds. The
offshore winds will continue through Sunday morning before
weakening Sunday Afternoon. The strongest winds will be near the
coastal foothills and below passes and canyons where gusts to 45
mph will be possible. Monday will likely be the warmest day, with
90+ degree temps from within 1-2 miles of the coast inland to the
foothills. The very warmest locations for inland coastal areas
into the western valleys could have high temperatures near 100 on
Monday.

For Tuesday and Wednesday...the high pressure aloft over Southern
California will begin to weaken in response to a low pressure
trough moving in from the northwest. This will bring a return of onshore
flow which slowly strengthens. Temperatures will begin to decrease
near the coast and spread inland with night and morning coastal
low clouds and fog returning and spreading farther inland later in
the week.

For Thursday and Friday...Temperatures continue to decrease and
onshore flow strengthens as the approaching trough deepens off the
California coast. The increasing onshore flow could bring periods
of gusty west winds to the mtns and adjacent desert areas.
Medium-range deterministic models show a chance for some precip
on Fri. This is dependent on whether or not moisture from the sub-
tropics gets entrained as the trough absorbs an upper level low
currently located at about 35N 140W.

Chances of precip should end next Saturday as the trough axis
moves east.

&&

.AVIATION...
142100Z...East to northeast winds of 15-25 KT through Sunday morning
with the strongest surface gusts of 35-40 KT expected through/below
passes and canyons of the San Bernardino and Riverside County Mts
producing MDT-STG UDDFS and LLWS over and west of the mtns,
including near KONT and KSBD.

&&

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

&&

.FIRE WEATHER...
High pressure aloft will strengthen over Southern California
bringing a warming trend through Monday. Mostly weak offshore flow
will continue into Sunday. Winds will then weaken late Sunday
into Monday. Lowest daytime humidities will be 5 to 10 percent
each afternoon through Monday...with Sunday being the driest day.
Overnight recovery will be poorest near the coastal foothills
where mixing from winds continues overnight. Periods of gusty
northeast to east winds near the coastal foothills and below
passes and canyons will continue at times through Sunday morning.
The stronger winds are expected to be in the Inland Empire below
the Cajon and Banning Passes and near the coastal foothills of the
Santa Ana Mountains. The strongest gusts will be mostly around 45
mph.

&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Red Flag Warning until noon PDT Sunday for Orange County Inland
     Areas-San Bernardino County Mountains-Including The
     Mountain Top And Front Country Ranger Districts Of The San
     Bernardino National Forest-San Bernardino and Riverside
     County Valleys  -The Inland Empire-Santa Ana Mountains-
     Including The Trabuco Ranger District of the Cleveland
     National Forest.

PZ...NONE.

&&

$$

PUBLIC/FIRE WEATHER...PG
AVIATION/MARINE...Brotherton



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