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Area Forecast Discussion (AFD)

Issued by San Diego, CA (SGX)

FXUS66 KSGX 140430 AAA

Area Forecast Discussion
National Weather Service San Diego CA
930 PM PDT Fri Sep 13 2019

It will be hot and dry inland through Saturday, while a shallow 
marine layer moderates temperatures along the coast with patchy fog 
nights and mornings. A Pacific trough will bring cooler weather, a 
deepening marine layer, and gusty mountain and desert winds early 
next week. Onshore flow will continue through the week with coastal 
low clouds and patchy fog nights and mornings, and seasonal late 
summer temperatures.



Evening Update:

This evening at 9 pm the temperature trends are in line with the 
ongoing forecast database. The 00Z RAOB from KNKX shows a shallow and 
weak marine inversion. Cloud cover is expected to be patchy only 
near the immediate coast, so the forecast was updated to back off 
the cloud cover a bit. Patchy dense fog will still be a concern but 
back off until late tonight when the best chance would be. No other 
changes to the forecast.

Previous discussion, issued earlier today at 147 PM PDT:

Some heat inland and some dense coastal fog are the focus through 
Saturday. Inland relative humidity in the single digits has allowed 
temps to skyrocket this afternoon. San Bernardino is up to 102 and 
Thermal is up to 108 so far. Patchy dense fog was along the coast 
this morning, and a similar situation is expected early Saturday 
morning and again early Sunday morning. While dense fog will not be 
widespread, look out for it if you're traveling along the coast the 
next couple mornings. Max temps will be nearly identical Saturday to 
those occurring today. A low pressure trough will deepen and swing 
into the West Sunday and Monday. That will bring cooler weather and 
deepen the marine layer. Coastal low clouds should extend a little 
farther inland Sunday night and again Monday night. The trough will 
grab some high level moisture in the form of high clouds Sunday 
night and Monday. That could lead to a sprinkle or two Monday 
morning in the mountains, but there's really no chance of measurable 
rain. The trough axis goes through SoCal Monday night. Coastal 
clouds will probably get into the inland valleys Tuesday morning. 
Tuesday appears to be the coolest day, with max temps 5-10 degrees 
below average. Strong onshore winds through mountains and adjacent 
deserts could reach 45 mph gusts for those favored spots late 
Monday. Previous guidance showed some high pressure and offshore 
breezes to follow this trough passage next week. Latest guidance 
scraps that idea. No ridge appears and we are left with a gradually 
weakening trough pattern. That would bring a very modest warming 
trend bringing temps back to average the latter part of next week.



140415Z...Coast/Valleys...Patchy stratus/fog will occur overnight 
and early Sat morning within 8 miles of the coast, mainly San Diego 
County. Most likely time will be 11Z-15Z Sat, though confidence of 
timing is just moderate. There is about a 50% chance SAN will have a 
CIG late tonight/early Sat. Bases will generally be 300-600 ft MSL 
with tops to 800 ft MSL. Local vis will be less than 1 mile in fog. 
Most areas should clear 14Z-17Z Sat with VFR conditions prevailing 
Sat afternoon and most likely Sat evening.

Mountains/Deserts...Mostly clear with unrestricted vis through 
Saturday evening. 


Patchy dense fog with visibility less than 1 NM will be possible 
late tonight through early Saturday morning and then again late 
Saturday night through early Sunday morning. Otherwise, no hazardous 
marine weather is expected through Wednesday. 


Hot and very dry inland through Saturday. Daytime humidity around 5-
10 percent in the far inland valleys, mountains and deserts this 
afternoon and again Saturday afternoon. Onshore flow increases 
Sunday and Monday for improvement in humidity and some cooling. A 
low pressure trough moving in from the northwest will bring gusty 
westerly winds to the mountains and deserts Monday into Tuesday.
Portions of the mountains could have very low relative humidity
for a short time during the winds.


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