Does CA have a winter blend gas starting November?

I just refilled at Costco, Tustin, CA on November 2 and immediately saw mpg drops ever since (for 2 days). In my communting route, I can easily achieve over 60 mpg. But in the past 2 days, I have to try hard to maintain 55 mpg. I don't fill any less power. It has to be the gas. Does CA have winter blend gas starting in November every year? Or else.

In looking at my fuel mileage spreadsheet, it looks like over the last 2 years, winter blend gas came in (Bay Area) at the end of Nov/beginning of Dec.

Anyone in SoCal knows the switching date from summer blend to winter blend? I checked on the web and couldn't get a concrete answer.

I just did an email exchange with Gary Richards (Mr. Roadshow) of the San Jose Mercury News.

Summer blend gasoline comes to the Bay Area no later than May 1st. He said that it varies by region (he thought So. Cal gets it earlier, like April 1). I didn't get info regarding when winter blend gas comes in, although as I mentioned earlier, I see it in Bay Area gas stations at the end of Nov/beginning of Dec.

Hope that helps.