From John Chesnut:

High likelihood of Central California rain beginning Thursday this week. These are trailing rain bands from low pressure systems crossing the high North Pacific.

Genesis: a nearly stationary low near Kauai, Hawaii was blocked by persistent high pressure centered over the Western states. This high pressure will drift westward and displace the low. The movement of the high pressure opens a channel along the west coast for shortwave rain bands to be pushed south.

On an even broader scale, the movement of the high and low pressure couple is a consequence of the periodic progression of the “Madden Julian Oscillation [MJO]” eastward across the tropical Pacific.

The MJO is a paired pattern of high convection (thunderstorms) and dry descending air linked in the Indian and Pacific Ocean along the equator. It moves eastward from the Horn of Africa to the coast of Peru in a 30-90 day cycle. The eastern most phases (near the coast of South America) of the MJO weaken or split the North Pacific jetstream, which allows the prototypical western North American high to detatch from the western desert and drift westward across the Pacific.

The El Nina pattern (with high Ocean temperatures) has been observed to strengthen the impact of the MJO ( whereas the El Nino (Pacific storm)pattern overpowers and suppreses it). The El Nina pattern (and general climate warming) slows the eastward drift of the MJO in the Pacific (and shortens its residence in the Indian Ocean).

As of 8 am this morning, 12/9, Big Sur has had between .20 and .25” since last night.