Area Forecast Discussion
Issued by NWS San Diego, CA

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FXUS66 KSGX 201510

Area Forecast Discussion
National Weather Service San Diego CA
810 AM PDT Sat May 20 2017

High pressure aloft will continue warm weather through Tuesday, with
temperatures around 10 degrees above average. The warming will peak
near the coast today, then slowly back off through Tuesday as the
marine layer returns and slowly deepens. Cooler all areas by
Wednesday as low pressure moves inland to the north, increasing the
onshore flow for the latter half of the week. This will deepen the
marine layer further, push daytime temperatures back below average,
and result in gusty westerly winds across the mountains and deserts.
Warming returns next weekend as high pressure rebuilds aloft.



Satellite imagery this morning indicated completely clear skies
across the Southland, including the CA Bight. Marine stratus was
well west of the islands at 8 AM PDT. The 12Z atmospheric sounding
from Miramar showed a layer of moderate easterly winds above 6K FT,
peaking at 35 KT around 9K FT MSL. Modest warming of the column
below 15K FT spiked to 9 degrees C 700 FT above the surface. Surface
dewpoints all the way to the coast remained depressed in the low-mid
40s F. Surface pressure gradients were holding at about 4 MBS
offshore NV to KSAN, and weak onshore to the lower deserts with an
overall weak onshore trend.

The forecast was updated to boost temperatures a few more degrees
today, based on the sounding this morning, otherwise the forecast is
on track.

From previous discussion...

High pressure aloft off the West Coast and weak offshore flow will
bring warmest high temperatures for coastal and western valley
areas today with high temperatures 10 to 15 degrees above average.
Weak onshore flow will return for tonight through Tuesday with
patchy stratus returning near the coast late tonight into early
Sunday morning with slowly increasing coverage and inland extent
through Tuesday as the marine layer slowly deepens. Slow cooling
will spread inland for coastal and valley areas for Sunday through

Farther inland...slow warming will continue for today through
Tuesday with high temperatures in the lower deserts peaking on
Tuesday around 10 degrees above average with high temperatures
around 107.

For Wednesday through Friday...a trough of low pressure will move
inland to the north with stronger onshore flow for Southern
California. High temperatures slightly above average near the
coast on Wednesday and 4 to 8 degrees above average for inland
areas...will cool to slightly below average on Friday. The marine
layer will continue to deepen with areas of night and morning low
clouds and fog spreading farther into the valleys. The stronger
onshore flow will also bring gusty southwest to west winds to the
mountains and deserts each late afternoon through late evening.

High pressure aloft will return near the West Coast next weekend
with slow warming.


201449Z...Primarily P6SM vis and mostly SKC for all areas through
21/0600 UTC. 21/0600-1600 UTC, there`s a chance that patchy dense
fog/low stratus will develop within 5 SM of the coast. Bases of low
stratus would be 200-400 ft msl with tops around 500 ft msl.
However, confidence in low stratus/dense fog impacting KSAN, KCRQ
and KSNA is low at the moment, with greatest chances for dense fog
occurring during the 21/1200-1500 UTC time-frame. Otherwise, P6SM
vis and mostly SKC continuing.


Patchy dense fog may develop over the coastal waters early Sunday
morning into Sunday night, and perhaps into Monday as well.
Otherwise, no hazardous marine weather is expected through Wednesday.


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





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