Weather Service Report


069 
FXUS66 KSGX 230413
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
913 PM PDT Wed Sep 22 2021

.SYNOPSIS...
After today's heat, Southern California will start to see some
cooler weather through much of the next week. An area of low
pressure will bring cooler weather as well as a chance for showers
and storms mainly across the mountains and into the deserts for
Thursday into early next week. Another larger trough of low 
pressure will impact the West Coast by early next week providing 
additional cooling, stronger onshore flow and an increase in 
night and morning low clouds.

&&

.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...

The ridge of high pressure over the Desert Southwest that brought
us the last several hot days is being displaced to the southeast
as SoCal begins to come under the influence of a low pressure
trough moving inland to the north. Temperatures this afternoon
were not quite as high as yesterday and only one high temp record
was tied. The cooling trend begins in earnest tomorrow when daytime
temperatures are likely to be on the order of 5-15 degrees lower 
than today.

The trough moving inland to the north will move into the Great
Basin and will likely develop a closed low over southern Idaho by
Thu morning. This low is expected to move southward to a position
in the vicinity of the lower Colorado River basin on Fri. There is
general agreement on this solution across deterministic and 
ensemble models, however there are minor differences in the timing
and trajectory that create some non-trivial uncertainty with
respect to the sensible weather outcomes.

Most likely it will result in cooler weather and a deeper marine 
layer, along with the chance of showers and thunderstorms, mainly
over the mountains and lower deserts. Models also indicate that 
this area of low pressure will become nearly stationary over 
SoCal and Arizona into the weekend. For now, the highest chance of
precipitation will be on Saturday afternoon. Ensemble models 
still do not have a great grasp on this system, but a fair amount 
continue to show light precipitation amounts overall.

This low pressure system will depart to the east on Monday as another
large trough of low pressure from the Gulf of Alaska makes its way 
the Golden State early next week. This will lead to increasing night
and morning low clouds across the western valleys to the coast 
along with cooler weather and stronger onshore flow. Depending on
how strong this system becomes will determine how much we cool 
off. Current indications are that the coolest day will be next
Wednesday when the upper deserts will be in the low 80s and the
lower deserts will be mostly in the mid 90s.

&&

.AVIATION... 
230330Z...SCT100-200 tonight and Thu except for areas SCT-BKN005 
over the coastal waters and in vcnty KSAN from 12-16Z Thursday with 
local vis 1-3 miles in FG/BR.

&&

.MARINE...
No hazardous marine weather through Sunday. Wind gusts to 20 kts 
over the Outer Waters Thursday afternoon.

&&

.FIRE WEATHER...
After another hot an dry day, there will be only modest humidity 
recovery in the inland areas tonight. For Thursday through the 
weekend, a weak low pressure system will enter the Desert 
Southwest and will bring a cooling trend and a gradual recovery in
humidity for inland areas. There is also a slight chance of 
thunderstorms, mainly in the mountains each afternoon Thursday 
through Sunday. Uncertainty is still moderate to high but the
potential for afternoon thunderstorms cannot be ruled out.

&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.

PZ...NONE.

&&

$$

PUBLIC/FIRE WEATHER...PG
AVIATION/MARINE...Moede

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