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Area Forecast Discussion (AFD)

Issued by San Diego, CA (SGX)

FXUS66 KSGX 162005

Area Forecast Discussion
National Weather Service San Diego CA
105 PM PDT Sun Jun 16 2019

Weak low pressure aloft will maintain typical June weather with near 
to slightly below normal daytime temperatures and marine clouds and 
local fog spreading well inland each night. Midday clearing back to 
coastal areas is expected, but will likely be delayed or limited, 
especially over coastal areas on Monday. The deserts will be 
seasonably hot under fair skies. Slight warming is expected midweek 
as a ridge attempts to build aloft, but a return to cooler weather 
is likely before next weekend as troughing returns. Dry, and cooler 
than average conditions are likley to develop all areas and persist 
into next week.



A weak trough aloft spread some feathery cirrus clouds across SoCal 
today, which were mainly seen inland due to persistent marine 
stratus closer to the coast. Surface pressure gradients were just 
beginning to trend more onshore, but were fairly weak at Noon PDT. 
For most wind-prone areas that meant peak westerly winds were under 
30 MPH.

It looks like we are about to see another rather dramatic shift in 
the upper air pattern over the North Pacific as a deep cold low 
pressure area over the Gulf of Alaska acquiesces to high pressure. 
The process occurs over this week, and by early next week models 
show a highly amplified ridge along 150W forcing the low pressure 
and associated cold air downstream, which in turn feeds persistent 
troughing over the West.

Over the next two days we will be experiencing the result of weak 
troughing aloft over the SW which actually becomes displaced by the 
building ridge over the EastPac, but only temporarily. As a matter 
of fact, Wednesday may be the only day we actually have the eastern 
extent of that Pacific Ridge over us. It will get squeezed back to 
the west Thu/Fri as the cold trough digs SE over the PacNW and 
northern Rockies. 

For SoCal it means typical June weather with lots of night/morning 
stratus lingering into the afternoons some days over coastal areas. 
Monday could be the most persistent, followed by a decrease Tue/Wed 
under the ridging. Wednesday should be the warmest day (about 
normal), then troughing from the north returns, which will help to 
rev up the onshore flow and start the cooling Thursday into next 
weekend. Daytime temps will be running some 5-10F below average, 
with the greatest anomalies in the mountains. Still quite 
comfortable, given how hot it could be this time of year. Of course 
in the deserts, mostly clear skies and below average temps is still 
hot. For Palm Springs it means forecasting a maximum daily 
temperature a few degrees south of the "century mark" on Saturday.

This pattern ensures no early return of the monsoon before the end 
of the month, which the extended runs of the GFS model still show 
some signs of attempting to emerge early next month.


161935Z...Coast/Valleys...Low clouds with bases 1000-1600 ft MSL are 
still clearing out of San Diego and Orange County valleys. Only 
localized intermittent clearing is expected along the coast this 
afternoon. Low clouds with bases 1000-1600 ft MSL, expected to 
spread inland overnight after 02Z. Local vis restrictions of 3-5 SM 
in BR/HZ in the valleys and higher terrain obscured in clouds. SCT 
conditions expected in the valleys by 17-20Z tomorrow, with only 
intermittent clearing at the coast after 20Z. 

Mountains/Deserts...Mostly clear with unrestricted vis today. West 
winds with sfc gusts 25-35 kt will occur along the mountain crests 
and desert mountain slopes and below the passes from 22-04Z, 
weakening overnight. Areas of up/down drafts are possible over and 
east of the mountains.


No hazardous marine conditions are expected through Friday. 


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