FXUS66 KSGX 172122
Area Forecast Discussion
National Weather Service San Diego CA
122 PM PST Sat Nov 17 2018
High pressure aloft will keep the weather fair and dry through next
Tuesday, with patchy night and morning low clouds and fog near the
Coast. A weak trough will develop off the Coast next weak and move
inland over the Holiday weekend, bringing cooling and higher
humidity. Rain will be likely over northern parts of California by
Wednesday. Some light rain could even survive the trip into Southern
California Wednesday night or Thanksgiving Day. The cooler weather
and higher humidity will prevail through the Holiday weekend, and
some light, marine layer precipitation will be possible at times as
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
Skies were fair across SoCal as high, cirrus clouds drifted from
west to east. There evidently was enough instability aloft for some
cirrus floccus with long ice crystal tails to develop, adding to
the diversity of cloud type. The sfc pressure gradient was weak,
keeping winds light most areas. Relative humidity remained very low,
except along the immediate coast.
High pressure aloft will force any incoming energy and moisture from
a weak Pacific low pressure area offshore, to the south. The net
affect of this interaction will drive better offshore flow through
Monday, keeping any meaningful rise in humidity confined to coastal
areas. See FIRE WEATHER discussion below for more detail. A more
significant trough will get carved out over the far EastPac during
the latter half of next week, bringing some needed rainfall to
northern and central portions of the State. As it swings farther
inland, some light precip could brush SoCal Wed night/Thanksgiving
Day. Since the system is weakening, prospects for much rain look
remote at this time with chances decreasing from north to south.
The flow aloft remains mostly zonal after the passage of the holiday
trough, keeping temperatures seasonal, and humidity levels elevated
in a fairly deep marine layer. The passage of additional weather
systems to the north may even squeeze some drizzle or light rain
from the marine layer west of the mts at times through next
weekend, but nothing heavy appears in the offing.
172100Z...SCT-BKN high clouds will continue to push in from the west
this afternoon and evening with bases at or abv 15000 ft MSL with
unrestricted vis. Potential exists for low clouds with bases AOB
1000 ft MSL, and Fog making an appearance late tonight along the
immediate coast and in some coastal valleys, though confidence is
low at this time.
No hazardous marine weather is expected through Wednesday.
.FIRE WEATHER...Widespread RH levels remained at 15% or less at
midday inland, and vegetation remains very dry, but winds are light.
Although there will be a slight onshore push this afternoon, winds
will turn back offshore tonight into Sunday, and increase Sunday
night into Monday. This will reinforce the dry conditions westward
into the valleys with minimum RH levels in the 10-20% range. Coupled
with the offshore winds of 15 to 25 MPH along the coastal slopes and
below passes and Canyons, fire weather conditions will again be
elevated late Sunday and Monday, although critical conditions are
not expected at this time.
SKYWARN... Skywarn activation will not be needed this weekend.
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