Wavenumber-1 to wavenumber-2 evolution in today's 00Z GFS. Highly uncertain - a lot will depend on the tropospheric evolution of the ridge near 0°E - but something to keep an eye on. Note also the barotropic trough anomaly around 60°W, which would help drive cold over N America. pic.twitter.com/8Hdh2ak18C

— Dr Simon Lee (@SimonLeeWx) December 11, 2019