Dense fog once again formed in pockets along the Central and Southern California coastlines due to a persistent upper level ridge that has been parked over the Eastern Pacific.

When a ridge is a constant feature an inversion develops for many sites along the California coastline. What that means is that the air at the surface is cooler than the air above which is the "inverse" of what is typical. Hence the name "Inversion". This happens because the air is cooled when it comes in contact with the cooler ocean waters. This is most typical in summer months when there is usually a large difference between ocean temperatures and the temperatures over the land. But this fall has not been typical and with a strong, stubborn ridge over the Eastern Pacifc, temperatures in Southern California have been unseasonably warm for an extended period.