411
FXUS66 KSGX 252021
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
121 PM PDT Sat May 25 2024

.SYNOPSIS...
Slightly cooler today in some areas, with gusty southwest to west
winds in the mountains and deserts. Only partial clearing of the
low clouds this afternoon. High pressure to the south will bring
some warming for Sunday through Thursday, more noticeable inland.
The marine layer will become shallower with night and morning
coastal low clouds only extending into western portions of the
valleys by the middle of next week.

&&

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

This afternoon, low clouds still cover most of the region west of
the mtns but there are now spaces between the elements of
stratocumulus through which sunshine is reaching the ground. We
expect to see more breaks in the clouds for a few more hours
before the coverage begins to increase again later this afternoon.
In some locations, temps are a little higher than at this time
yesterday and in some locations they are a little lower. Sfc
pressure gradients remain onshore with 4.2 mb SAN-DAG and 6.2 mb
SAN-IPL. Gusty westerly winds continue, with the wind-prone
locations reporting gusts of 35-45 mph locally up to 62 mph at
Whitewater. HiRes models indicate a weakening trend for the next
several days.

From previous discussion...
Troughing continues to dominate the pattern over the western U.S.,
bringing unseasonably low temperatures and breezy conditions
today. There is good consensus among ensemble members across model
platforms through Wednesday then solutions tend to diverge more.
Indications are for the trough to move east on Sunday, allowing
for height rises with near-zonal flow aloft. This will produce
somewhat higher temperatures and reduced coverage of marine layer
low clouds. Daytime highs will be 5-10 degrees higher on Sunday
away from the coast, though still several degrees below normal.
There will likely also be better clearing of the low clouds
inland, although clearing at the coast could be restricted if the
height rises were to strengthen the marine layer inversion.

Through Wednesday, the upper level high centered over central
Mexico will gradually shift westward and a north-south ridge axis
will amplify downstream of a low pressure system intensifying in
the Gulf of Alaska. There will be competition between the trough
associated with the low and the building ridge. For SoCal this
will likely result in modest warming across the region on Monday
with little variability through Wednesday. Daytime high temps
will generally be close to seasonal normals during this period. The
effects to temps will be much more significant over the Great
Basin and the Rockies. The marine layer will be shallower, with
low clouds and fog limited to the coastal areas and western
valleys each night and morning, and there will be a better chance
of clearing each afternoon including on the Memorial Day holiday.

After Wednesday, ensemble solutions begin to diverge significantly
with respect to the progression and strength of the low pressure
system in the Gulf of Alaska as it moves across the Pac Northwest
and the subsequent ridging that follows behind it. About 50% of
ensemble members favor more of a ridge/warmer weather over the
west coast, 25% a trough with cooler weather, and 25% somewhere
in between. The cluster analysis suggests that members favoring
either solution generally break down by model platform. Members
from the same model platform tend to favor similar solutions. This
continues into the weekend. The temperature forecast reflects the
NBM solution which maintains near seasonal temps through the end
of the week.

&&

.AVIATION...
251945Z...Coast/Valleys/Coastal Slopes...SCT-BKN with bases 2000-
4000 FT MSL are occurring over some coastal areas this afternoon,
with some reverse clearing at the coast also evident on satellite.
Additional clearing should occur across the Inland Empire/inland
Orange County through 22z with limited clearing across southern San
Diego County this afternoon. Widespread BKN-OVC again tonight-Sun
morning. Bases will be similar, if not slightly lower than today,
generally in the 1500-2500 FT MSL range.

Mountains/Deserts...Mostly clear through tonight. W-SW gusts of 20-
35 kt continuing through 10z Sun, with MOD UDDFS over/east of the
mountains. Local VIS 3-5 SM will occur in local BLDU.

&&

.MARINE...
West to northwest winds around 20 knots will occur in the outer
coastal waters each afternoon and evening through Monday.

&&

.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...PG
AVIATION/MARINE...Adams