Area Forecast Discussion
Issued by NWS San Diego, CA

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000
FXUS66 KSGX 141633
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
933 AM 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 from
this morning into 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...

This morning...satellite imagery shows patches of low clouds over
the coastal areas and localized radiation fog inland under clear
skies. This should all burn off or mix out by 11 o`clock as the
offshore flow develops. Currently, the sfc pressure gradients are
-9.8 mb SAN-TPH but the gusty northeast winds have not yet developed.

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 strengthen later this morning and continue
through Sunday morning before weakening Sunday Afternoon. The
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.

&&

.AVIATION...
141600Z...Marine stratus with bases near 1000 FT MSL and tops 1500-
2000 FT MSL this morning will slowly scatter out and push to the
coast by 18Z. East to northeast winds of 15-25 KT will develop along
the coastal mtn slopes/foothills this morning after 18Z, 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 develop today and 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 will develop near the
coastal foothills and below passes and canyons this morning and
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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