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000 
FXUS66 KSGX 180943
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
243 AM PDT Wed Oct 18 2017

.SYNOPSIS... 
A deepening trough over the West will bring a cooling trend 
and more marine layer clouds through Friday. On Saturday the flow
turns offshore as high pressure builds. That will bring Santa Ana
conditions, clear skies and hot weather next week.

&&

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

Scattered high clouds and just a hint of fog around Imperial Beach 
are all we got in the sky this morning. Today will be cooler as a
low pressure trough deepens to our north and onshore flow 
increases. This trough will also help spin up a coastal eddy that 
will rebuild a marine layer and develop some coastal clouds. 
Patchy coastal clouds should develop tonight into Thursday, then 
increase and spread over the entire coastal basin Thursday night 
and Friday morning. For a brief time Friday morning these coastal 
clouds will thicken enough to produce patchy drizzle west of the 
mountains. The increased onshore flow will produce westerly winds 
through mountain passes and into the deserts Thursday evening and 
night. Top gusts in top spots will exceed 40 mph. Still breezy 
Friday, but not as strong. The trough moves through the interior 
West Friday night and high pressure begins to build over 
California this the weekend. The marine layer will get somewhat 
suppressed and diminished by early Saturday and then the offshore 
flow will flush it out completely. Offshore pressure gradients 
from the Great Basin don't look too steep Sunday, but they max out
Monday and Tuesday mornings for some gusts in the foothills that 
could exceed 35 mph in spots. At the same time high pressure 
really builds on top of California to bring more heat. Offshore 
flow will bring legitimate warm Santa Ana conditions with those 
winds. The winds do not look very strong or very widespread, but 
will help cook the already hot air and push it to the coast. 
Temperatures appear to top out Monday and Tuesday with lots of 
90s, even at a few beaches, along with some 100-degree readings at
lower elevations. It will be a dry heat to be sure, and that also
means nights will cool off efficiently.

&&

.AVIATION... 
180840Z...SCT clouds AOA 15000 ft through Wednesday with unrestricted 
vis. Low clouds and fog is unlikely this morning. Low clouds/fog 
will likely return late this evening.

&&

.MARINE...
No hazardous marine weather is expected through Thursday. Winds will 
increase to 20-25 kt in the outer coastal waters late Thursday night 
and Friday, decreasing by Saturday.

&&

.BEACHES...
A south southwest swell from 200 degrees from 3-4 ft/17 seconds will 
peak today. This will produce 3-6 ft surf with sets to 7 ft over 
Orange County and northern San Diego County. Highest surf will be on 
southwest facing beaches. Strong rip and longshore currents will 
accompany the elevated surf. Swell and surf will lower Thursday but 
surf to 6 ft with strong rip currents will continue. As a result, 
the beach Hazard Statement has been extended to 5 pm Thursday.

&&

.FIRE WEATHER...
Hot and dry weather will return this weekend as high pressure
builds aloft and offshore flow develops. The dry air and winds
will start through and below the Cajon Pass on Saturday, then
spread across the entire region Sunday. Offshore winds will peak
Monday and Tuesday mornings, and those days will be the hottest
and driest as well. Relative humidity will fall to single digits
Sunday through Tuesday away from the coast. Humidity recovery 
will be poor in localized areas where winds persist during the 
nights. Critical fire weather conditions are likely at least in 
the windy areas of the foothills and downstream valleys.

&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Beach Hazards Statement through Thursday afternoon for Orange 
     County Coastal Areas-San Diego County Coastal Areas.

PZ...NONE.

&&

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