The initial piece of energy, which is weaker, will bring widely scattered showers Monday night into Tuesday. The stronger upper low will swing under the belly of the system in the Gulf Of Alaska and then approach the our area Tuesday night into early Wednesday. This will bring rain and occasional downpours. Isolated thunderstorms will also be possible Wednesday as colder air aloft arrives in the region.
I'll be the first to admit that storms like this (broken in pieces) can be difficult to forecast. The amount of rain we receive is largely dependent on the strength of the storm as is passes. This second wave has me concerned because it will be intensifying as it passes overhead, giving us a wider range of possibilities. This is compounded by the threat of thunderstorms, which means that some people might see torrential rain, while others might not see much at all.
At this point, I think the computer forecasts are being a tad too aggressive, especially GFS, which has been terrible with storm placement and strength lately. Below are the NAM projected rain totals through Wednesday evening. You can see that we could potentially get about an inch of rain. Also notice the heavier amounts for Northern California.
Yet another system could pass the area on Saturday. I'll focus on that system later in the week. Afterwards, it looks like the start of next week (Sun-Mon 12/21-12/24) will be mild and dry for Southern California as an upper level ridge nudges into the West Coast (marked on the map below).
