Area Forecast Discussion
Issued by NWS San Diego, CA

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000
FXUS66 KSGX 171040
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
240 AM PST Sun Dec 17 2017

.SYNOPSIS...
Upper level low pressure over northwest Mexico will move eastward
today with residual mid level moisture and clouds over the
mountains and deserts of San Bernardino...Riverside...and San
Diego Counties continuing into this morning...then decreasing
during the late morning and afternoon. Surface high pressure over
the Great Basin will bring periods of stronger and gusty northeast
winds along and below coastal mountain slopes through today.
Warming with weaker winds for Monday and Tuesday. Another low
pressure system moving through the Great Basin will bring cooling
and strong gusty west winds for the mountains and deserts for
Wednesday...followed by strong gusty northeast winds for
Thursday...weakening Friday. Dry with warming and weaker winds for
next weekend.

&&

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

.SHORT TERM (Today through Tuesday)...
Upper level low pressure centered over northwest Mexico early this
morning will move eastward across northern Mexico today.
Overnight...there have been bands of thunderstorms to the north
and east of the center. Mid level wrap around moisture has
extended into portions of Southern California with the mountains
and deserts from the San Bernardino Mountains southward on the
western edge of the more significant moistures...generally
centered in the 600 to 700 mb layer with mid level clouds keeping
skies mostly cloudy in some of these areas. This moisture and the
clouds are expected to extend past sunrise...with the moisture
decreasing and the clouds dissipating later in the morning and
through the afternoon with some residual clouds near the mountains
possible.

Surface high pressure over the Great Basin will bring periods of
stronger and gusty northeast winds along and below coastal
mountain slopes through today. The stronger and more widespread
winds are expected in portions of San Bernardino...Riverside...and
Orange Counties along and below coastal mountain slopes with areas
of northeast winds 20 to 30 mph with gusts to 45 mph with
isolated gusts to 65 mph below the Cajon Pass and near the
coastal foothills of the Santa Ana Mountains. The strongest and
most widespread are expected from after sunrise through the
morning...then decreasing and becoming more localized during the
afternoon and evening. Winds are expected to be not as widespread
nor strong in San Diego County and confined mostly to the
mountains and inland valleys. Through 2 AM...strongest gusts have
been to around 55 mph along the coastal slopes of the Santa Ana
Mountains.

High temperatures will slowly warm into Tuesday with slightly
above average high temperatures for Tuesday.

&&

.LONG TERM (Wednesday through Saturday)...
A low pressure system along the Pacific Northwest coast early
Wednesday...will move into the Great Basin Wednesday night...and
into the central and southern Rockies on Thursday. This will bring
stronger onshore flow for Southern California for Wednesday and
Wednesday night with stronger and gusty west winds for the
mountains and deserts. It will also bring cooling for Wednesday
and Thursday and possibly a brief return of coastal low clouds for
Wednesday night into Thursday morning. Lower level flow will go
offshore on Thursday with a period of moderate strength northeast
winds on Thursday...weakening Thursday night and Friday. The
ECMWF and GFS are in better agreement for Friday into next weekend
over the eastern Pacific and along the West Coast with high
amplitude ridging developing just off the West Coast. For Southern
California...this will continue the dry weather with weaker winds
and warming to near to slightly above average high temperatures,

&&

.AVIATION...
171030Z...SCT-BKN clouds with bases around 10000 ft MSL will prevail
through 18Z today, then gradually dissipate. Vis will be
unrestricted through Monday. N to NE winds 15-30 knots with gusts 35-
45 knots along coastal slopes/foothills and through/below the
canyons and passes will create MOD-STG UDDFS/LLWS over and SW of the
mountains. Strongest winds will be north of San Diego county. Winds
will gradually weaken after 23Z this afternoon.

&&

.MARINE...
The WNW swell will dissipate today, with maximum seas early this
morning around 8 feet in the outer coastal waters. Some gusts around
20 knots will occur today but should remain below Small Craft
Advisory criteria. Otherwise, no hazardous marine weather is
expected through Thursday.

&&

.FIRE WEATHER...
Upper level low pressure over northwest Mexico will move eastward
today with residual mid level moisture and clouds over the
mountains and deserts of San Bernardino...Riverside...and San
Diego Counties continuing into this morning...then decreasing
during the late morning and afternoon. This will keep humidities
for much of the mountains other than the lower coastal slopes
falling below critical thresholds today.

Surface high pressure over the Great Basin will bring periods of
stronger and gusty northeast winds along and below coastal
mountain slopes through today along with lower humidities. For San
Bernardino...Riverside...and Orange Counties...this will bring areas
of northeast winds 20 to 30 mph with gusts to 45 mph with isolated
gusts to 55 mph below the Cajon Pass and near the coastal
foothills of the Santa Ana Mountains.

The strongest and most widespread winds during the morning with
lowest humidities winds this morning with lowest humidities from
late morning through the afternoon. Lowest daytime humidities of
around 15 percent are expected in portions of the Inland Empire
and inland Orange County.

Winds will weaken for tonight and Monday.

&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Red Flag Warning from 8 AM this morning to 8 PM PST this evening
     for Orange County Coastal Areas-Orange County Inland Areas-
     Riverside County Mountains-Including The San Jacinto Ranger
     District Of The San Bernardino National Forest-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-San Gorgonio Pass Near Banning-Santa
     Ana Mountains-Including The Trabuco Ranger District of the
     Cleveland National Forest.

     Wind Advisory until 8 PM PST this evening for Orange County
     Coastal Areas-Orange County Inland Areas-San Bernardino
     County Mountains-San Bernardino and Riverside County
     Valleys-The Inland Empire-San Gorgonio Pass Near Banning-
     Santa Ana Mountains and Foothills.

PZ...NONE.

&&

$$

PUBLIC/FIRE WEATHER...17
AVIATION/MARINE...Maxwell



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