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000 
FXUS66 KSGX 171608
AFDSGX

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

.SYNOPSIS...
Low pressure over the Lower Colorado River Valley today will 
keep gusty northeast winds over the mountains, and through and below 
canyons and passes, strongest to the north of San Diego County. 
Lighter wind Monday and Tuesday with seasonal temperatures. Strong 
onshore flow will develop Wednesday, pulling in the marine layer 
briefly, then turn back offshore with gusty northeast winds again 
through the passes, and along the coastal foothills. Fair skies will 
prevail, with cooler conditions Wednesday, then a bit warmer by the 
weekend. 
  

&&

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

Satellite imagery early this morning showed low pressure spinning 
over far NW Mexico, slinging some moisture and clouds back to the 
west across eastern portions of the CWA. This moisture eased the 
dryness across the region at mountain top and in the mid-levels last 
night. The 12Z Miramar sounding still had moist layer between 9K and 
15K FT. Winds were NE up to 20KT below 8K FT. The sfc pressure 
gradient was still weakly onshore KSAN to the lower deserts, but was 
13 MBS offshore from SW NV. The strong offshore gradient was fueling 
N-NE winds 25-40 MPH with gusts 50-60 MPH in offshore wind-prone 
areas of Orange, San Bernardino, and Riverside Counties. Peak gust 
through 8 AM this morning has been 65 MPH at Fremont Canyon.

No forecast changes this morning. 

From previous discussion...

.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... 
171603Z...Areas of SCT-BKN clouds AOA 10000 ft MSL will prevail 
through 1800 UTC, then dissipate 1800-2200 UTC. P6SM vis will 
continue through Monday morning. N to NE winds 15-30 knots with 
gusts 35-50 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. 
High confidence in KONT being impacted by surface wind gusts of at 
least 35 kt this morning, and possibly up to 45 kt, with winds 
starting to weaken by 2000 UTC. Meanwhile, moderate confidence in 
KSNA getting surface wind gusts of 25-30 kt this morning, with winds 
starting to weaken by 2000 UTC. Winds and associated UDDFS/LLWS 
across the area will gradually weaken 2000 UTC through Monday 
morning. 

&&

.MARINE...
7 am buoy reports indicate 8-9 foot seas in the outer waters and 4-7 
foot seas in the inner waters. These numbers indicate a trend 
downward in wave heights from previous hours. The west-northwest 
swell will continue to dissipate today, with seas lowering to 3-6 ft 
in the outer waters and 2-4 ft in the inner waters by this evening. 
Some northeast to east wind gusts could reach 20 knots today, 
remaining just below Small Craft Advisory criteria. No hazardous 
marine weather is expected through Thursday.

&&

.FIRE WEATHER...
A Red Flag Warning remains in effect for portions of the Inland 
Empire, Santa Ana Mts, Orange County coastal plain, and lower 
coastal slope and foothill areas of Riverside and San Bernardino 
Counties for strong northeast winds/gusts, and several hours of 
marginal RH values near 15%. Elevated conditions farther south, 
mainly due to stronger offshore flow.

Low pressure over far northwest Mexico will move eastward today with 
residual mid-level moisture over the mountains and deserts of San 
Bernardino...Riverside...and San Diego Counties this morning, then 
decreasing through the day. This will keep RH levels over the 
mountains (other than the lower coastal slopes) from falling to 
critical thresholds today. 

Northeast winds of 20 to 35 MPH with gusts 50 to locally 65 MPH this 
morning over wind-favored northern portions of the forecast area. 
Lower speeds in general for San Diego County at 15 to 25 MPH with 
gusts 35 to 40 MPH. Peak gusts around 50 MPH on the windiest coastal 
slopes. RH values are expected to remain above 15% most areas.

The winds will ease tonight and Monday. Strong and gusty onshore 
flow returns late Wednesday for the mts/desert slopes.

&&

.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.

&&

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