THEWEATHERMOGIL:: Winter finally arrives!
As December’s warmth fades into short-term memory, folks nationwide are going to start shivering. Don’t be surprised if you start to hear a transition from, “OMG, it’s soooo warm,” to, “this cold is horrible…wish the weather would warm up.”
This transition will be linked to a significant shift in the upper level wind flow pattern. The eastern U.S. ridge is going to be replaced by the evolution / relocation of the infamous “Polar Vortex.” Meanwhile, the western U.S. trough will be transformed into a strong upper level ridge (Fig. 1). Note that such upper air wind flow transitions (a.k.a. “flip flops”) are not uncommon.
Based on computer models, the general cool down across the U.S. will be continuing. The chilling will be most profound where the weather has been the warmest (i.e., the eastern U.S.). By mid-month, some mornings will see freezing temperatures in every one of the 48 contiguous states. By mid-month, sub-zero readings may be affecting northern Minnesota, the Dakotas and parts of northern New England.
Linked to this cool down will be an active southern branch of the jet stream. This will allow for storminess to affect California and the southwest U.S. and then spread wintery weather conditions across the central U.S. Redevelopment of low-pressure systems along the East Coast will ensure that snow will become a factor in eastern U.S. weather by around Jan. 11. Current computer models suggest a major East Coast snow event from about the Washington, DC area northeastward into New England.
As always, any forecasts/outlooks beyond a few days should always be viewed and acted upon carefully. Meteorology involves a complex interaction of many atmospheric variables, such that forecasts can sometimes change dramatically.
© 2016 H. Michael Mogil
Originally published 1/3/16