Here is a Pacific satellite picture showing the storms. The first storm is west of San Francisco around 40N 140W, part of a double-barrel structure. The second storm in the series is out around 45N and 168W.

The first storm will bring the heaviest rain to the northern half of the state while the second storm aims its heaviest rain at the southern half. The first storm will bring rain inland along the north-central and northern coast Wednesday morning and spreads the rain east and south during the day. Rain will move into Southern California Wednesday night, except in the San Diego area where it may not rain much until near dawn Thursday. There will be a period of strong and gusty winds on the central and northern coast and in the mountains with this first storm. Snow levels will be high, 7,500 feet or a little higher around Tahoe and above 8,000 feet in Southern California. Expect rain amounts of 0.75 to 1.50 inches in north-central and northern California with 0.50 to 1.00 inch in the Central Valley. On the west-facing slopes, I think 1.50 to 2.75 inches falls on average. In Southern California, expect 0.33 to 0.75 of an inch around the Los Angeles Basin and more like 0.20 to 0.40 of an inch in the San Diego area.

There will be a lull on Thursday. Any leftover rain Thursday morning in the south will end. There can be a couple of showers around anytime Thursday in the northern third of the state but nothing heavy or prolonged.

The second storm has some very impressive dynamics with it, more so than with the first storm, with a strong mid-level jet bringing copious amounts of moisture and lift aimed at Southern California. Here is the GFS at 12Z Friday showing the amount of precipitable water. Notice the nose of 1.2 to 1.5 inches aimed right at Southern California.

The low-level jet will also help to enhance rain amounts on south-facing mountains from Santa Barbara County to Ventura and Los Angeles County. Rain will fall everywhere in the state Friday and Friday night with the heavy rain mostly in the southern third of the state. Along with the rain expect another round of gusty wind. Expected rain amounts are 0.50 to 1.25 inches in north-central and northern California with 1.00 to 1.50 inches in the Central Valley. In Southern California around the Los Angeles Basin, I am thinking 2.00 to 3.00 inches of rain in a lot of places with the south-facing mountains picking up 3 to 6 inches. Somewhat lower amounts are likely in San Diego but still a big storm with 1.00 to 2.00 inches on average. Snow levels will fall from 7,500 to 5,000 feet in the northern and central Sierra and drop to 5,500 feet in Southern California by late Friday night. Snow levels Saturday in a more showery pattern drop to 4,500 to 5,000 feet. Snow totals at the resorts in Southern California will be 1 to 2 feet with local amounts somewhat higher. Around the Tahoe resorts and Mammoth, I am looking for 1 to 3 feet.

Here are rain and melted snow totals through the day Saturday from the GFS.

Do note though, the European is giving about an inch more of rain/melted snow to the southern third of California than the GFS. And this model could very well be right. My forecast is certainly leaning more on the upper end of rainfall amounts between the two models.

These storms are certainly very much needed and welcome. However, with any storm of this magnitude, there are going to be problems. The rain will cause local flooding problems especially in low-lying spots. This can bring travel difficulties on some roads, even freeways. Second, the heavy rain on recent burn areas brings the high risk of mudslides and debris flows. If you live near these areas, be ready to get out in a hurry if authorities ask you to do so. Air travel delays are also likely at times because of big hubs such as SFO and LAX will have to slow the amount of arrivals and departures during times of heavy rain and gusty winds. It will not be if there will be delays it will be how many delays there will be.

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