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Area Forecast Discussion (AFD)

Issued by San Diego, CA (SGX)

FXUS66 KSGX 122208

Area Forecast Discussion
National Weather Service San Diego CA
210 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. 



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. 


122100Z...Coast/Valleys...Mostly VFR conditions will continue this 
afternoon. Patchy low clouds, with bases around 1500 ft MSL and tops 
near 1800 ft MSL, may develop along the coast early tonight before 
offshore flow develops. Confidence in low clouds affecting coastal 
aerodromes tonight is low.

Mountains/Deserts...East to northeast surface wind gusts of 30-40 kt 
are possible Thu morning along coastal mountain slopes and 
foothills. Otherwise, FEW/SCT high clouds through the period.


No hazardous marine weather is expected through Sunday.


Skywarn activation will not be needed through Thursday.