*Annual Rainfall is based on the California Water Year,|
which runs from October 1 through September 30.
FXUS66 KSGX 121558
Area Forecast Discussion
National Weather Service San Diego CA
855 AM PDT Wed May 12 2021
Weak high pressure aloft will bring seasonal May Gray weather west
of the mountains through Thursday. The mountains will be warm both
today and tomorrow, and it will be hot in the deserts. A trough of
low pressure moving into the area this weekend will bring cooler
weather, a much deeper marine layer, and a chance for showers west
of the mountains Saturday night and Sunday morning. Strong west
winds will impact the mountains and deserts.
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
Cloud bases this morning were around 1,200 ft MSL, 400 feet lower
than Tuesday morning. The inversion strength remains strong, still
at 8C on the 12Z NKX sounding, so like yesterday the marine layer
clouds will slowly dissipate back to the coast through early
afternoon. Scattered to broken low clouds may linger a few of the
beaches through the afternoon.
No changes to the forecast this morning. We are evaluating the
strength of the trough that will impact SoCal this weekend, with a
focus on the precipitation chances and amounts west of the
mountains Saturday night and Sunday morning.
*From Previous Discussion*
The warming trend will continue today with high temperatures 5 to
locally 10 degrees above average for the deserts, mountains, and
inland valleys. The marine layer will keep high temperatures
slightly below average for coastal areas into the western San
Diego County valleys. Inland areas may warm another degree or two
on Thursday while the valleys begin to cool.
Cooling will begin to spread inland on Friday as a weak low
pressure system approaches the west coast. The marine layer will
begin to slowly deepen with coastal low clouds spreading a little
farther into the inland valleys for Friday morning.
.LONG TERM (Saturday through Tuesday)...
A low pressure system from the northwest will move slowly
southeastward across California during the weekend. This will
strengthen the onshore flow and deepen the marine layer with a
cooling trend continuing through Sunday.
The coastal low clouds should cover most of the valleys for
Saturday and extend onto the coastal mountain slopes for Sunday
morning. There is the potential for a period of more rapid and
substantial deepening of the marine layer for Saturday night into
Sunday morning with the marine layer deepening to around 6000
feet. There remains the potential for some drizzle or light rain
from this deeper marine layer for late Saturday night into Sunday
morning inland to the coastal slopes of the mountains.
With the cooling during the weekend, high temperatures on Sunday
will be around 5 degrees below average at lower elevations to 10
to 15 degrees below average in some of the mountain and inland
valley locations. With the stronger onshore flow, there will be
periods of stronger and gusty southwest to west winds in the
mountains and deserts for Saturday into Sunday with the stronger
gusts in the windier locations to around 45 mph.
For early next week, the low pressure system will move east with
warming for Monday and Tuesday. The marine layer will begin to
decrease in depth, but still be deep enough for the night and
morning coastal low clouds and fog to cover much of the valleys.
121540Z...Coast/Valleys...Low clouds are covering much of the
coastal basin this morning with bases 1000-1700 FT MSL and tops 2000-
2500 FT MSL. Reduced vis where low clouds intersect terrain. Low
clouds to scatter out 16-17z across inland valleys, and 17-19z near
most coastal areas, though some locations may not fully clear.
Widespread low clouds will redevelop 01-03z Thu, with similar
coverage and bases.
Mountains/Deserts...Mostly clear with unrestricted vis today and
No hazardous marine weather is expected through Sunday.
Skywarn activation will not be needed through Friday.