Area Forecast Discussion
Issued by NWS San Diego, CA

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FXUS66 KSGX 242048

Area Forecast Discussion
National Weather Service San Diego CA
147 PM PDT Sat Mar 24 2018

A low pressure trough along the West Coast will maintain onshore
flow and cool weather this weekend under a deep marine layer with
areas of night and morning low clouds and patchy fog extending onto
the coastal slopes. A few light showers or sprinkles are possible
again tonight into early Sunday as well. A warming trend begins on
Monday as offshore flow shrinks the marine layer and high pressure
builds along the West Coast for the balance of the week.



At 1 PM PDT...Satellite imagery showed marine stratus rapidly
developing and moving north, just offshore of the San Diego County
Coast. Gusty S-SW winds were accompanying this development along the
immediate coast. The sfc pressure gradients were accelerating
onshore. From KSAN to SW NV it was 10 MBS, and KSAN to the lower
deserts was about 7 MBS. Peak wind gust reports of 25 MPH or more
were more widespread over the San Diego County Mts and across desert
areas than this morning.

Moderate onshore flow will continue a deep marine layer with a
chance of some sprinkles or scattered light rain showers along and
west of the mts through Sun morning. It will remain cool as well
with daytime highs running between 6 and 12 degrees below average.

A low pressure area off the PacNW coast will drift inland over the
intermountain West and weaken through Mon. At the same time, energy
spinning off this system will deepen the trough over CA, with the
axis forecast to pass SoCal Mon afternoon. Thickness values (sfc-500
MB) fall through 12Z on Mon, and then slowly recover on Mon
afternoon as winds turn northerly. This begins the scouring process
for what is left of the marine air. The ensuing offshore pattern
will dominate next weeks weather, largely limiting any marine
influence to the coastal strip. This will keep any low clouds and
fog to a minimum.

A ridge will replace the departing low over the far EastPac early
next week, peaking along 130W on Wednesday, then deflate and be
replaced by a weak low pressure trough next weekend. The process
looks dry, but there will be a variation in daytime highs with
warming each day to 6 to 10 degrees above average by Thu, then
cooling to just a few degrees F above average next Sat. The offshore
pattern will support periods of gusty easterly winds through and
below passes and canyons each morning Tue-Thu.


242030Z...Coasts/Valleys...Multiple SCT/BKN low cloud decks, with
bases from 3000-5000 ft MSL, will continue through this afternoon.
Stratus will then refill the coastal basin this evening and
overnight, with slightly higher bases. -DZ is possible at times
tonight, mainly in the foothills, as the marine layer deepens. Low
clouds will become more SCT by late Sunday morning.

Mountains/Deserts...SCT high clouds and P6SM VIS through Sunday
morning. Westerly surface wind gusts of 30-45 kt will develop over
and east of the mountains this afternoon and continue through Sunday
morning. Areas of LLWS and strong UDDFS likely east of the
mountains, including near KPSP and KTRM.


Northwest wind gusts of 25 to 30 kt are expected over the waters at
times through Monday night, with strongest gusts across the outer
waters. Small Craft Advisories have been issued for the area through
2 AM Tuesday. The winds, along with combined seas of 7-10 ft at
times and steep waves, will produce hazardous boating conditions.


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


PZ...Small Craft Advisory until 2 AM PDT Tuesday for Coastal Waters
     from San Mateo Point to the Mexican Border and out to 30 nm-
     Waters from San Mateo point to the Mexican Border Extending
     30 to 60 nm out including San Clemente Island.



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