Area Forecast Discussion
Issued by NWS San Diego, CA
FXUS66 KSGX 232051
Area Forecast Discussion
National Weather Service San Diego CA
200 PM PDT Sun Oct 23 2016
A trough of low pressure will move through the region through Monday
and bring up moisture from the south. This will bring scattered
showers tonight and Monday. Instability aloft will also bring a
slight chance of thunderstorms through Monday. While the cooling
trend will continue this afternoon and Monday, temperatures will stay
a little above normal for late October. A high pressure ridge will
develop over the West and bring fair weather Tuesday and Wednesday
except for patchy coastal stratus and fog, with warming by
Wednesday. A rather deep low pressure trough will bring a chance of
precipitation late in the week, though the deepest moisture will
stay to the northwest.
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
Light showers were moving over parts of the area this afternoon,
with greatest concentration over the Inland Empire and San
Bernardino County Mountains, with a few stations recording measurable
precipitation, under 1/10 inch. So far, the dry layer below 750 MB
has resulted in evaporation of much of the precip. A few lightning
strikes have occurred today over the coastal waters.
The trough is roughly 1000 miles west of San Diego, and the trough
axis will move through late Monday or Monday evening. Until then,
the bottom of the moist unstable layer will gradually lower to as low
as about 800 MB tonight and Monday. This will bring a better chance
of measurable precipitation, though most areas will have less than
1/4 inch, but a few mountain locations could have locally around 1/2
inch due to being above most/all of the low-level dry layer. More
thunder could happen again tonight into Monday as NAM and WRF
show instability in the 700-500 MB layer, with WRF MU-CAPE values of
200-400 J/kg through Monday morning with some surface-based CAPE
over the mountains Monday afternoon. The system will move east of
the area late Monday night and end the precip threat then.
Because of cloud cover and a moderately warm profile, minimum temps
will be 10 degrees above normal tonight, with slightly above normal
max temps Monday.
The upper high will build over the western US, but further east than
our latitude Tue-Wed, so we will have surface onshore flow and some
marine layer stratus near the coast. Temps will remain a little
above normal, especially inland, with some warming Wednesday and
possibly Thursday. A rather deep trough will form over the east
Pacific and tap into some tropical moisture, with the possibility of
a tropical system moving by to the south/southwest of southern Baja
contributing to the moisture. Models currently have the best
moisture and precipitation to our northwest, but some precip,
possibly up to 1/2 inch, could occur over some of our forecast area
sometime Thursday night through Saturday. More precip could occur
early the following week due to the positioning of the long-wave
trough over the East Pacific.
232045Z...Patchy stratus may develop again tonight with bases near
1500 ft MSL.
Scattered showers will continue this afternoon and evening, with
mostly light rainfall. Isolated thunderstorms are possible as well
this afternoon and continuing into Monday. Otherwise SCT-BKN cloud
layers at/above 6000 ft MSL and unrestricted vis through Monday
Scattered light showers will move over the coastal waters later this
morning. There is also a slight chance of thunderstorms late this
afternoon through Monday, with the main impact being cloud-to-water
lightning. The Marine Weather Statement continues the thunderstorm
potential through this evening.
There is a slight chance of thunderstorms this afternoon through
Monday as an upper level trough lifts northeast across Southern
California. Cloud-to-ground lightning could occur, resulting in a
danger to beach goers and swimmers.