Area Forecast Discussion
Issued by NWS San Diego, CA

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FXUS66 KSGX 210415

Area Forecast Discussion
National Weather Service San Diego CA
900 PM PDT Fri Sep 20 2019

Fair and warmer weather is expected over the weekend, with limited
night and morning low clouds and fog near the coast. A low pressure
system will bring partly cloudy skies and slight cooling Monday and
could bring enough moisture from the south to bring a few showers or
thunderstorms Tuesday through Thursday. A broad trough of low
pressure moving into the West Coast will bring additional chances of
precipitation late next week.



Skies were clear this evening with mostly light winds. High
temperatures recovered to just slightly below seasonal normals
overall, and the 00Z NKX sounding had generally 1-3 deg C warming
below 800 MB. That warming trend will continue Saturday as the upper
level ridge moves over, along with further warming aloft. Stratus
will be very limited tonight along the coast as a combination of the
subsidence plus some northwest flow along the immediate coast this
evening makes the marine layer more shallow, and stratus off the
northern Baja coast appears to be drifting a little bit south.

The forecast for next week is a bit low confidence right now as GFS,
ECWMF and Canadian/GEM ensemble solutions show substantial
variability with the position of the closed low after it moves
southeast over the far western US Monday, and the remnants of
Hurricane Lorena move north over or near Baja California. Most
likely, the main moisture will stay just to our east, but 1/3 to 1/2
of the solutions are far enough west that some showers or possibly
thunderstorms could form over our forecast area of extreme
southwestern California. Some moisture from Lorena will likely
interact with the low in some way, and instability of the cold core
low certainly could enhance any convection. Chances of any heavy
rain is fairly low right now, but I did add slight chances of
showers or thunderstorms to parts of the area Tue-Thu, mainly in the
afternoons/evenings. The mountains would be the most favorable
location for convection, but lower elevations are not exempt. If the
upper low ends up to our east, some offshore flow could develop,
though models generally do not have much wind as there is no cold
air mass over the Great Basin to advect in and help enhance any
mountain waves. Temperatures will depend on the upper low position
but will likely be near or just slightly below normal. Regardless,
the marine layer stratus should be limited, either if there is an
offshore flow solution or upper low/convective solution. Ensembles
are mostly showing a deep trough over the West Coast the following
weekend (28-29 Sep) but with differences in timing by a day or two.
This would likely bring cooler weather, some showers and locally
strong westerly winds starting as early as Friday.


210200Z...Coast...Low confidence forecast tonight. Low clouds are
expected to develop first in San Diego County, starting as early as
07Z, but most likely after 09Z. CIGS should arrive quite a bit later
at KSNA, and there`s a chance they may not even appear. Moderate-
high confidence in at least some periods of prevailing BKN-OVC at
KSAN/KCRQ 10Z-16Z. Bases will be lower tonight, around 800-1200 FT
MSL, and locally below at KCRQ. CIGS will mostly be confined to the
immediate coast, with VIS restrictions of 2-4 SM likely in areas a
few hundred feet MSL 10-16Z. High confidence in terminals clearing
by 16Z Saturday.

Valleys/Mountains/Deserts...VFR conditions will prevail through
Sunday, with CLR skies and unrestricted VIS.


No hazardous marine weather expected through Wednesday.


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





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