Source: everlaneToday in SF it’s 36º. Just last week we were in the high 60’s. We’ve been bundled up in cashmere all week at the office and have been wondering what has caused this drastic change in temperature?With a little research we found out that winter’s cold is felt as the jet stream dips southward in North America. Usually it dips later in January. This year, however, the flood of arctic air has gotten a much earlier start.It’s going to be a long cold winter. Bundle up.