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Area Forecast Discussion (AFD)

Issued by San Diego, CA (SGX)

FXUS66 KSGX 130538

Area Forecast Discussion
National Weather Service San Diego CA
938 PM PST Wed Dec 12 2018

A Santa Ana weather pattern will bring gusty winds to the mountains 
and foothills tonight and Thursday. Thursday will be a warmer day in 
the coastal and valley areas, and a cooler day in the mountains and 
deserts. The weather will be dry and mild through the weekend, 
followed by clouds and perhaps a chance of light rain Monday as a 
weak trough moves inland. On Tuesday, high pressure builds over the 
Southwest for dry, mild weather through Friday. 




Patchy low clouds are seen off the coast on satellite imagery.
Offshore flow should keep these off the coast. Offshore winds will
pick up through the passes and along the coastal mountain slopes.
30 mph reported just below the Cajon Pass past hour. Latest WRF
is not aggressive with wind speeds, and this model usually
overdoes speed. Gusts in the most wind prone locales could reach
40+ mph, but not meeting advisory criteria and no significant
impacts are expected. See previous discussion below for further 
forecast details.

...Previous Discussion (Issued at 210 PM PST Wed Dec 12 2018)...

Pressure gradients from the Great Basin have trended offshore at a 
pretty good pace since sunrise, increasing from 0.0 to -6.3 from San 
Diego to Tonopah. A shallow marine layer kept temperatures in the 
mid 60s in the coastal and valley areas early this afternoon, which 
is a little below average. Mountain and desert areas will be a 
little above average today. 

This temperature regime flip-flops on Thursday with the onset of a 
Santa Ana pattern that will bring warming west of the mountains and 
cooling to the mountains and deserts. Coastal and valley highs will 
be in the 70s, with an 80 degree high possible at some sites in 
inland  Orange County sites where downslope warming will be the 
greatest. Mountain highs will in the 50s, High Desert highs in the 
upper 50s, and Lower Desert highs in the upper 60s to low 70s.  

As for the winds, a 1040 mb surface high settles over southern 
Idaho, strong enough to support a period of gusty offshore winds 
later tonight through Thursday morning. This won't be a terribly 
strong offshore wind event, but there will be gusts to 45-50 mph in 
the windiest Santa Ana prone mountain passes and eastern valleys. 
The offshore winds abate Thursday afternoon through Friday morning, 
followed by weak onshore flow Friday afternoon. 

On Saturday and Sunday a weak trough passes through bringing high 
clouds but nothing much more than that. Temperatures will be a 
little warmer than average, and winds will be fairly light. 

A Pacific trough moves inland Monday for cooler weather and small 
chances of light rain. The ECMWF continues it's stronger, wetter 
trend with a closed low traversing SoCal Monday. The GFS is much 
weather with a more progressive wave moving inland farther north 
across central California. On Tuesday a high amplitude ridges builds 
in behind the trough and will bring sunny, mild days through Friday. 


130415Z...A few low clouds with bases around 1500 ft MSL will 
continue along the coast through about 09Z. CIGS at the coastal TAF 
sites are unlikely, though some may have a brief period of 3-5 SM 
vis in BR 06-10Z. Otherwise a few high clouds and unrestricted vis 
through Thursday evening.

NE-E surface wind gusts of 30-40 kt are possible Thu morning along 
coastal mountain slopes and below the passes and canyons. Winds will 
weaken Thu afternoon. 


No hazardous marine weather is expected through Sunday. A large WNW 
swell arriving Monday may generate combined seas of over 10 ft.


Skywarn activation will not be needed through the week. 




PUBLIC...Gregoria (Update)/Moede (Prev Discussion)