Over the next 4 weeks in this CFSv2 forecast, the height anomaly pattern across North America evolves from the "Pacific Trough" regime (bringing very mild weather across the continent) to the "Alaskan Ridge" regime, associated with much colder conditions. (1/3) pic.twitter.com/CxHS5ey4aD

— Dr Simon Lee (@SimonLeeWx) January 21, 2020