Some very interesting atmospheric and oceanic events around the world may very well be signaling a change to the overall weather pattern here in the northeastern US as we progress through the second half of the month to one that is stormier and colder. The northeastern US has largely avoided any sustained cold weather during the month of December and accumulating snow has been quite sparse. At the same time, several regions around the world have suffered through some serious cold spells with snow including in much of Europe, Asia, western Canada and Alaska.
To begin with, there has been a sudden warming of stratospheric temperatures in the northern latitudes in recent days. This sudden change in the upper atmosphere followed several weeks of orderly temperature drops. Secondly, a daily index that is tied to the tropical Pacific Ocean sea surface temperature pattern called the Southern Oscillation Index (SOI) has plunged in recent days deep into negative territory following several weeks of slightly positive readings. If sustained, negative SOI readings can indicate some warming of sea surface temperatures in tropical Pacific waters which can, in turn, help to activate the southern jet stream across the US. Finally, another index that we closely monitor here during the winter season is the North Atlantic Oscillation (NAO), and it has dropped sharply in recent days into negative territory. A sustained negative NAO can be a leading indicator to a stormier and colder pattern in the northeastern US depending on some other factors. Some of the computer forecast models are now picking up on a stormier pattern in coming weeks for the northeastern US; however, it is likely that the models will have all kinds of difficulty and variability during this pattern transition period - and we’ll continue to monitor it at thesiweather.com.