By SETH BORENSTEIN
AP Science Writer
Winter has started out weird in the United States. It’s been flip flop weather in much of the country with the Pacific Northwest getting record rainfall while Denver and the Rockies still are waiting for their first significant snowfall of the season. Meteorologists say a stuck jet stream, the river of air that brings weather systems west to east, and La Nina, the flip side of El Nino, are the main causes. The planet also gets more weather extremes with climate change. Even though astronomically it’s still fall, meteorological winter starts Dec. 1. But no one told the weather that this year.