Area Forecast Discussion
Issued by NWS San Diego, CA
FXUS66 KSGX 210517
Area Forecast Discussion
National Weather Service San Diego CA
917 PM PST Mon Feb 20 2017
It will be mostly dry with cooler than average days due to
continued onshore flow. A storm system moving by to the north will
spread some clouds and a slight chance for light precipitation into
portions of Orange, Riverside and San Bernardino counties through
Tuesday. Otherwise partly cloudy. Cooler and breezy for Wednesday
and Thursday, then a bit warmer again on Friday as flow aloft
turns more westerly. Cooler with increasing clouds into the
weekend, with a chance of precipitation for Sunday through early
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
Variable clouds cover much of the region this evening as a low
pressure system passes to the north over Central California. This
system is producing light showers as far south as Los Angeles
County and a few of those showers could stray even farther south
tonight through Tuesday. Precipitation continues to our north
through Wed as a broad low pressure trough with embedded
shortwaves dominates the pattern over the East PAC/West Coast. On
Wed, the trough deepens enough to bring strong an gusty west winds
to SoCal, mainly in the mtns and the deserts. As the trough axis
shifts eastward, the flow aloft becomes northwesterly bringing
drier conditions. The fair weather continues through Sat even as
the flow aloft becomes more westerly. Through this period, daytime
temperatures will likely remain a few degrees below seasonal
From previous discussion...
Beginning on Sat, medium-range numerical models indicate that the
longwave pattern will undergo a significant shift as a strong
ridge of high pressure builds over the EastPac near 160W and a
shallow, broad trough develops over North America. In addition,
the ridge over the EastPac is forecast to form a closed upper high for
a time over the Gulf of Alaska late in the week, which frequently
results in low pressure systems moving southward out of the
Arctic. The West Coast is downstream of this developing rex block,
and in an unstable northerly flow pattern where shortwave troughs can
deepen and form cut-off lows separated from the westerlies.
This instability has been exhibited in recent ensemble and
deterministic global model runs, which show large solution spreads
beyond about 120 hours. This translates into a low confidence
forecast from late in the weekend into next week across SoCal.
With that in mind...The numerical models continue to adjust their
solutions but still indicate the potential for wet weather Sun
through early next week as a low pressure system moves into SoCal
from the northwest.
210447Z...SCT to BKN clouds over the coast and valleys, with
variable bases 1500-3500 ft msl and variable tops up to 4000 ft msl
through Tuesday. Isolated -DZ/-SHRA possible in Orange and San
Bernardino counties, producing brief vis restrictions 3-5 sm.
Elsewhere, SCT-FEW clouds AOA 8000 ft msl and P6SM vis.
Northwesterly winds and seas will increase Wednesday through
Thursday, with winds reaching 15-25 kt with gusts to 30 kt, and seas
reaching near or above 10 feet. This will result in conditions
hazardous to small craft during that time.
Moderate swells will continue to bring elevated surf of 3-6 feet.
Strong rip current activity is likely through most of this week. A
large, medium period west-northwest swell varying from 280 to 290
degrees will build early Wednesday, peak late Wednesday through
early Thursday at around 12 ft/14 seconds, then lower the rest of
Thursday. This will likely result in another round of high surf of
around 6-9 feet.
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.