What is this stuff???

We have spent the past 4 days driving over 1400 miles...Arizona to Louisiana. We arrived in Lake Charles, LA this afternoon. This picture was taken on I-10 on our way from Houston, Tx to Lake Charles. LA. The forecaste for the next several days is much of the same....rain...thunderstorms....rain. But that is not going to stop us from seeing this area of the country. Quack...Quack.