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Area forecast discussion 
National Weather Service San Diego California 
210 PM PDT Thu may 24 2018 


Synopsis... 
a deep trough over the west will bring cooler than average weather 
and a deep marine layer through Saturday. Areas of drizzle are 
possible west of the mountains Friday and Saturday mornings. Gusty 
west winds are forecast in the mountains and deserts Friday 
afternoon through Saturday. On Sunday the trough will weaken for 
warmer days and better clearing west of the mountains Monday and 
Tuesday. 


&& 


Discussion...for extreme southwestern California including Orange... 
San Diego...western Riverside and southwestern San Bernardino 
counties... 


Short term (today through saturday)... 
rain and drizzle were widespread in the San Diego and Orange County 
coastal and valley areas this morning. A rainfall summary has been 
headlined on our webpage. The highest amount was 0.15" at Bee Canyon 
in the foothills of the Santa Ana Mountains. 


Clearing was very slow today (or nonexistent in some areas) due to a 
very thick 3-4kft cloud layer. Skies cleared in the southeast 
sections of the inland Empire near Perris and Hemet, but skies 
remained mostly cloudy in the Orange and San Diego County coastal 
and valley areas. 


A deep trough off the California coast this afternoon will move 
inland into central California Friday. The marine layer will remain very 
deep tonight and Friday, and there may be areas of light rain or 
drizzle again tomorrow morning. The one change is that cold air 
advection aloft with the trough will weaken the inversion through 
Friday morning. 850 mb temps of 14c this morning lower to 9c Friday 
morning. So despite the deep marine layer, this weaker inversion may 
promote better mixing and a greater chance for earlier clearing from 
the valleys both Friday and Saturday. The trough and the 
accompanying strong onshore surface gradients will bring strong and 
gusty west winds to the mountains and deserts Friday and Saturday 
afternoon and evening. 


It will be cool on Friday and Saturday compared to where 
temperatures should be for late may, with high temperatures near the 
coast a few degrees below average, and from 10-15 degrees below 
average in the valleys, mountains and deserts. 


Sunday through Wednesday...the trough over the west fills and 
weakens as it moves east over the Great Basin. The marine layer will 
be shallower with higher pressure aloft for less marine layer cloud 
intrusion into the inland valleys. The higher heights will also lead 
to warmer days. 


Beyond Wednesday...a weak trough moves inland along the West Coast 
Wednesday and Thursday for minor cooling, but it will be much weaker 
than our current system and temperatures will be at or just a little 
below average for the latter half of next week. 


&& 


Aviation... 
242030z..coast/valleys/coastal mountain slopes...stratus deck with 
bases 2000 to 3000 mean sea level and tops to 5000 ft mean sea level persist. May see a 
few hours of clearing for inland terminals 22-03z but coastal 
terminals likely to retain broken-overcast conditions. Clouds will quickly 
spread back inland 25/03-06z. Overall the cloud deck should be 
thinner tonight with slightly higher bases around 2500 feet and tops 
around 5000 feet. Patchy fog and drizzle expected late tonight and 
early Friday (10-15z). Models indicate faster and more widespread 
clearing on Friday with terminals expected to go scattered 17-20z Friday. 


Mountain crests/Desert Mountain slopes/deserts...winds will be the 
primary concern. Expect northwest winds 15-25 kts with a few gusts 
25-35 kts possible 21z-06z. This may result in localized low level wind shear with 
moderate uddfs over the mountain crests and into the deserts. Similar 
conditions are expected Friday afternoon/evening except the gusts 
could be a bit stronger. 


&& 


Marine... 
west northwest winds with gusts near 20 knots are possible Friday 
night through Saturday evening. Winds will weaken Sunday into early 
next week. 


&& 


Beaches... 
will extend beach hazards statement through Friday. A long-period 
south swell of 3-5 ft/14-15 sec will continue to produce elevated 
surf and hazardous swimming conditions through Friday mainly over 
Orange and northern San Diego counties. Sets to 6-7 ft are possible. 
Surf will begin subsiding Friday night. 


&& 


Skywarn... 
Skywarn activation will not be needed today. 


&& 


Sgx watches/warnings/advisories... 
California...beach hazards statement through Friday afternoon for Orange 
County coastal areas-San Diego County coastal areas. 


Pz...none. 


&& 



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