Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Diego California
845 PM PDT Friday Sep 30 2016
a low pressure trough will slowly move across California this
weekend bringing cooler and breezy weather Sunday and Monday. The
strongest westerly winds will surface in mountains, deserts, and
coastal waters. Marine layer cloudiness will become progressively
more extensive each night and morning with drizzle possible Sunday
night into Monday morning. Dry with modest warming Tuesday through
Discussion...for extreme southwestern California including Orange...
San Diego...western Riverside and southwestern San Bernardino
Skies were clear this evening with little low cloud development at
the coast through 8 PM. However the vis was down to 3 miles at Red
Beach and 6 miles at Imperial Beach, and temp/dew point spreads were
less than 5 degrees at the coast. So expect areas of low clouds and
fog to form later tonight in the coastal zones.
Friday was yet another very warm day in what has been week of hot
weather. Cooling is just around the corner though. A deep upper low
west of British Columbia will move south Saturday and develop into a
longwave trough along the West Coast. Saturday will still be another
warm day here in socal, but not quite as warm as today. Sunday and
Monday will be noticeably cooler by about 10 degrees as the trough
axis sweeps across socal.
As the trough moves in Sunday, breezes will pick up everywhere,
particularly in the mountains and deserts during the afternoon and
evening. Preliminary estimates on top gusts for the windiest spots
will exceed 50 mph. Monday it will really feel like fall with
breezy/windy weather and daytime highs at or below average.
The marine layer will deepen over the weekend in the increasing
onshore flow and an intermittent coastal eddy. Low clouds will
spread farther inland Sunday and Monday, and it may be deep enough
for areas of drizzle west of the mountains Monday morning. Light
measurable precip is possible on the foothills and lower mountains
The tough moves out Tuesday and is followed by weak ridging that
will bring modest warming and weak offshore flow Wednesday and
010345z...coast/valleys...patchy low stratus and fog could develop
late tonight along the coast and reach a few coastal airports.
Confidence is low with occurrence and timing, but the most likely
period of stratus/fog would be 11z to 16z Sat. If clouds develop,
bases will likely be below 800 ft mean sea level with patchy vis below 2 miles
and a small possibility of dense fog with vis 1/4 mile or less.
Mostly clear skies with unrestricted vis will prevail Saturday after
16z with a better chance of stratus/fog Saturday night with higher
Mountains/deserts...mostly clear skies with unrestricted vis will
prevail through Saturday night.
no hazardous marine weather is expected through Saturday. An area of
low pressure moving inland along the California coast will produce
unsettled conditions Sunday afternoon through Monday. Northwesterly
wind gusts during this period are expected to be 25-30 kt for the
outer coastal waters, with combined seas of 6-8 ft. A Small Craft
Advisory will likely be needed Sunday afternoon through Monday for
the outer coastal waters.
3-4 foot southerly swells from 190 degrees will bring 3-5 foot surf,
with occasional 6 foot sets north of Oceanside, through Saturday.
These swells may also produce strong rip and longshore currents at
the beaches. For Sunday into early next week, the southerly swell
will slowly diminish and mix with a building short period northwest
wind swell. This will result lower, but choppier surf conditions.
as a trough of low pressure generates strong onshore winds on
Sunday, there will be a time of low humidity below 15 percent
combining with those strong winds Sunday afternoon and evening
mainly on the Lee slopes of mountains and into parts of adjacent
deserts. However, the humidity quickly rebounds as the trough
arrives Sunday evening. Critical fire weather conditions may
happen, but only for a short time and only on isolated mountain
Lee slopes. Will continue to monitor, but at this time no
hazardous fire weather products are anticipated.
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.