http://d.weatherflow.com/navair/analysis.html
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Do you see the little white circles on top of this Naval Air map? National Weather Service Oxnard described this 6/6/12 L.A. weather as “offshore flow”: what they do is take air pressure (barometric) readings at inland sites like Barstow and even Bakersfield, and decide, e.g. whether these white circle locations are having ocean-to-land directions or land-to-ocean directions.

Note West/SW winds at the coastline and where most people live: We are not in a boat.