Area Forecast Discussion
Issued by NWS San Diego, CA

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912
FXUS66 KSGX 192014
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
114 PM PDT Fri Apr 19 2019

.SYNOPSIS...
A pair of troughs will move over Southern California this weekend,
ramping up the onshore flow and the marine layer. Gusty west winds
will accompany these systems over the mountains and deserts, and a
few light showers may develop as well, especially western San Diego
County. Cooler this weekend, then warmer next week as high pressure
builds aloft and onshore winds weaken and trend offshore, sending
temperatures back above average.

&&

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

At 1 PM PDT...Marine clouds covered the Bight, while higher bands of
altocumulus clouds drifted from south to north over the region.
Surface pressure gradients were weak, with the predominant wind
direction still from the east inland. Near Banning, a report
indicated east 15 Gust 25 MPH.

A weak upper-level trough is on track to move inland across SoCal
tonight, followed by another, more dynamic system from the northwest
on Saturday night. These systems will conspire to increase westerly
winds and build the marine layer inland to the coastal slopes. As it
deepens, some light showers could develop, especially in San Diego
County (along and west of the mts) Sat night. Once the second trough
passes, a third system form the north will drop south through the
Great Basin Sunday night, tightening up the onshore gradient one
more time late Sunday/Sunday night, before the gradient relaxes and
trends offshore late Monday/Tuesday morning.

The overall onshore gradient these systems will generate will keep
gusty winds over the mts/deserts, and below average temperatures
through the weekend. A warming trend will begin as the gradient
relaxes and trends offshore. Coastal warming is more uncertain as
there is a suggestion of an eddy developing over the CA Bight, which
could hold the marine layer there into early next week. As the week
progresses, a strong EastPac ridge is forecast to expand along the
West Coast before collapsing late next week. Warming looks more
certain for the midweek period when max temps should be 5-10F above
average most areas.

The main concern over the next few days will be the wind. Given the
support indicated, a Wind Advisory has been posted for Sat afternoon
through early Sunday over the mts/deserts when the strongest winds
are likely from the ridges, along the deserts slopes and into
adjacent desert areas. Winds will decrease some after Sunday
morning, but remain gusty from the northwest to North, through
Sunday night into early Monday as the upper low digs over the Great
Basin. While some light precip could fall Sat night, amounts look
negligible at this time.

&&

.AVIATION...
192000Z...Coast/Valleys...FEW-SCT clouds AOA 10000 FT MSL in the
valleys. FEW-SCT clouds AOA 1000 FT MSL along the coast. Moderate
confidence low clouds with bases 800-1000 FT MSL just off the coast
will cause periodic BKN conditions at coastal TAF sites before 02Z
Sat. BKN low clouds expected to impact coastal TAF sites 02Z-06Z
Saturday with cigs 800-1000 ft MSL and tops rising to near 2000 ft
MSL. Low clouds expected to move further inland tonight, impacting
KONT and KSBD after 9Z. Reduced vis 3 miles or less possible due to
fog at TAF sites and over higher terrain. SCT condition expected by
17Z Sat.

Mountains/Deserts...Mostly clear skies and unrestricted vis expected
through tomorrow afternoon. West winds are expected to pick up after
07Z Sat along mountain ridges, desert slopes, and through passes.
Sustained winds of 15-20 kt with gusts of 30-35 kt possible.

&&

.MARINE...
A brief period of NW winds 12-18 kt over the outer coastal waters is
expected this afternoon/evening. A Small Craft Advisory has been
issued for 05Z Sunday to 16Z Sunday for NW winds 10-15 kt gusting 20-
25 kt over the outer waters. Combined seas of 7-8 FT are expected
during that time period as well. Winds will weaken Sunday afternoon.
There is a slight chance of showers late Saturday night into Sunday
morning. No marine concerns are expected after Sunday.

&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Wind Advisory from 2 PM Saturday to 6 AM PDT Sunday for Apple
     and Lucerne Valleys-Coachella Valley-Riverside County
     Mountains-San Bernardino County Mountains-San Diego County
     Deserts-San Diego County Mountains-San Gorgonio Pass Near
     Banning.

PZ...Small Craft Advisory from 10 PM Saturday to 9 AM PDT Sunday for
     Waters from San Mateo point to the Mexican Border Extending
     30 to 60 nm out including San Clemente Island.

&&

$$

PUBLIC...10
AVIATION/MARINE...CO



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