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Area Forecast Discussion (AFD)

Issued by San Diego, CA (SGX)

FXUS66 KSGX 131731

Area Forecast Discussion
National Weather Service San Diego CA
930 AM PST Thu Dec 13 2018

Warmer west of the mountains today with gusty Santa Ana winds near
and below the coastal slopes of the mountains and below passes and
canyons. Onshore flow will bring cooling for coastal and valley
areas on Friday, with more mid and high clouds moving across the
area. A little warmer this weekend as a weak trough moves inland.
There is a small chance for some light precipitation on Monday, 
then dry and warmer into midweek as high pressure builds aloft and 
winds turn back offshore.



Skies were clear over SoCal at 9 AM PST. The sfc pressure gradient 
from SW NV to KSAN was around 9 MBS. This was supporting NE winds 20 
MPH with gusts to 30-35 MPH along the coastal foothills and through 
the passes. No changes to the forecast at this time. 

From previous discussion...

There will be high pressure aloft along the West Coast today with
surface high pressure over the Great Basin. Satellite imagery 
shows a few patches of stratus early this morning, mostly over the
coastal waters, with a few high clouds as well. The surface high 
pressure over the Great Basin will bring periods of gusty east to 
northeast winds near the coastal slopes of the mountains and below
passes and canyons. The mountains and deserts may be slightly 
cooler today than on Wednesday with several degrees of warming 
west of the mountains with greatest warming for inland coastal 
areas into the western valleys. 

For Friday, a trough of low pressure moving inland to the north 
will bring a return of onshore flow which will spread cooling into
coastal and valley areas. That trough of low pressure will also 
draw mid and high level subtropical moisture northward across the
area with more clouds on Friday into Friday night. Onshore flow 
will be weaker for the weekend with slightly warmer high 
temperatures for most areas.

For Monday, the range of model solutions for a trough of low
pressure moving inland across California has not changed much from
the past two days with the solutions ranging from a less 
amplified trough of low pressure moving inland faster to a little 
slower moving low pressure system that briefly closes off near the
California coast as it moves inland. The faster solutions would 
be mostly dry while the slower moving more closed solutions would 
bring more widespread precipitation and would more effectively 
tap a subtropical moisture plume directed into southern California
ahead of the low pressure system. The current forecast remains 
with an intermediate solution that would have a weakening front 
moving across southern California with some light precipitation 
possible for portions of southwest California. 

For Tuesday and Wednesday, high pressure aloft will strengthen  
along the West Coast with surface high pressure over the Great
Basin. This will bring a warming trend with periods of gusty
northeast to east winds near and below the coastal slopes of the
mountains and below passes and canyons.


131630Z...Clear skies with unrestricted vis will prevail through 
Friday. Areas of NE-E surface wind gusts of 25-35 kt are expected 
mainly in foothills and below passes through 21Z today, then mostly 
15-25 kt through Friday morning.


No hazardous marine weather is expected through Sunday. A large WNW 
swell Monday and Tuesday will likely generate seas of 10-13 feet, 
highest in the outer coastal waters (beyond 30 nm), though the 
period will be quite long, 18-20 seconds.


A large long-period (18-20 seconds) swell from the west-northwest is 
currently projected to arrive Monday and continue through Tuesday. 
The direction from 290 degrees will limit the effects somewhat, 
though surf of 6-12 feet is still quite possible, especially in 
southern San Diego County. Stay tuned in coming days to any hazard 
products as the swell approaches.


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