Area Forecast Discussion
Issued by NWS San Diego, CA

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FXUS66 KSGX 240406

Area Forecast Discussion
National Weather Service San Diego CA
906 PM PDT Tue Apr 23 2019

Warm days are ahead this week with high pressure building over the
Southwest through Friday. A shallow marine layer and a weak coastal
eddy will keep the coastal areas cooler. Night and morning low
clouds and fog west of the mountains will retreat back to the
beaches each afternoon. Sunday and Monday will be cooler with a
chance for showers as a trough of low pressure moves inland across
southern California.



Low clouds finally cleared from most of the coast late this
afternoon. With the exception of Huntington Beach northward, skies
are mostly clear this evening. Winds along the southern San Diego
County coast have turned southerly, indicative of a developing
coastal eddy. This will help bring low clouds and fog back to the
coastal areas, spreading around 10-15 miles inland by Wednesday
morning. The remainder of the forecast remains on track with no
changes this evening.

A warm upper air pattern will be in place this week with nearly
stationary high pressure aloft over the Southwest. Today the 500
mb heights rose from 570 dm to 578 dm. The valley, mountain and
desert temperatures responded in kind by warming 5-15 degrees
compared to yesterday. However, areas within a mile of the coast
didn`t see much warming due to the shallow marine layer and
scattered low clouds.

This will be the trend through Friday. It will be warm inland with
near steady 582 dm heights under a dome of high pressure. There may
be a few record highs too, primarily at Palm Springs and Thermal on
Thursday, where the record high of 102 at each station may be
reached or breached. Coastal temperatures will remain closer to
average due to a persistent shallow marine layer and weak coastal
eddy. The low clouds may be slow to dissipate too, as warming aloft
strengthens the inversion and slows the mixing.

The marine layer will be a little deeper tomorrow and areas within
15 miles of the coast may actually be a degree or two lower
tomorrow. Then on Thursday the marine layer turns a little shallower
for what looks to be a warmer day.

.LONG TERM (Saturday through Monday)...

A compact, yet potent, low pressure system over the Pacific will
approach SoCal Saturday for minor cooling and increasing onshore
flow. The GFS and ECMWF bring the trough directly over Southern
California Sunday and Monday. It`s still a long way away, but even
the ensemble mean shows a sharp trough, so confidence is a little
higher than normal at such a long range. The POP fields were
increased and the precipitation area was expanded Sunday and Monday
with this forecast package.


240400Z...Coast/Valleys...Areas of BKN/OVC stratus will develop
overnight within 15 miles of the coast with bases 600-1100 ft MSL
and tops to 1400 ft MSL. Timing of arrival of stratus at airports is
most likely to be between 06Z and 10Z. Areas of vis 1-3 miles will
occur 09Z-16Z Wed over higher coastal terrain, locally below 1 mile.
Most areas will clear 15Z-17Z Wed except for local stratus lingering
near the beaches through Wed afternoon. Stratus will spread back
onto land Wed evening.

Mountains/Deserts...Clear with unrestricted vis through Wednesday


No hazardous marine conditions are expected through Sunday.


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




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