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 Mon Apr 23 2018

Weak onshore flow will result in more widespread low clouds and fog
nights and mornings, otherwise fair and mild weather will continue
this week under weak high pressure aloft. Low pressure will move
toward the north coast of California late in the week, strengthening
the onshore flow, and deepening the marine layer. Areas of night and
morning coastal low clouds and fog will expand into the valleys,
along with cooling.



Marine clouds gathered quickly this evening along the coast, then
pulled back just after sunset for a time. Higher clouds spreading in
from the west were obscuring some of the lower clouds at 8 PM PDT.
The 00Z Miramar sounding had a weak 3 degree C inversion based near
1500 FT MSL. This was several hundred feet deeper than yesterday.
Dewpoints were higher inland as well this afternoon, but all things
considered, not a whole lot of change from yesterday. A few wind-
prone desert areas had peak gusts of 25 MPH, but winds were mostly

Given the lack of change in the synoptic situation, expect more fog
will form overnight with an emphasis on the coastal mesas, higher
terrain, and far western valley areas. No forecast changes are
anticipated, except for visibility improvement over the coastal
waters outlined below.

From previous discussion...

Weak high pressure aloft and otherwise benign synoptic pattern
will continue a deep marine layer contributing to night and
morning low clouds and fog each day through the end of the week,
with warm and sunny afternoons each day. Patchy dense fog could
bring some impacts near the coast and along the mesas each
morning. There will also be areas of brisk winds through mountain
passes and into adjacent deserts each evening, but with gusts
mainly 35 mph or less.

A low pressure trough will develop off the coast of Northern
California during the latter part of the week. Some model solutions
have it going northward this weekend, and others have it digging
southward, moving into Southern California around Sunday. These
solutions are bouncing around regarding the intensity of this
trough, but especially the timing of it. It could bring rain, or
nothing. We`ll need much more confidence before adding chances of
rain to the forecast. For now, the most responsible forecast is for
cooler weather with an expanded marine layer and more extensive
coastal clouds. Daytime temperatures look to sink below average by
the weekend.


240400Z...Coast...After a mid-evening break, areas of BKN-OVC
stratus and fog will likely spread around 10 miles onshore again
later tonight, though timing at airports is uncertain. Bases will be
700-1000 ft MSL with tops to 1400 ft MSL. Areas of vis 2-4 miles
will occur with local vis below 1 mile over higher coastal terrain.
Most of the stratus will clear 16Z-18Z, except for local BKN stratus
along the immediate coast Tue afternoon. Stratus will likely develop
again Tue evening.

Valleys/Mountains/Deserts...SCT clouds at/above 25000 ft MSL with
unrestricted vis will continue through Tuesday evening.


Patchy fog will occur over the coastal waters each night through
Wednesday, but visibility should remain above 1 NM. Stronger west to
northwest winds will develop in mainly the coastal waters beyond 30
NM each afternoon and evening Thursday through Saturday with gusts
between 20 and 25 knots possible


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





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