DISCUSSION: If you have ever wondered in the past or now currently wondering the reason for why the mercury is forecast to dip as low as the single digits across many parts of the north-central and northeastern United States, here is a great graphical answer to that question. Attached above is what is referred to an ensemble backward air parcel trajectory suite. These ensemble backward air parcel trajectories allow atmospheric scientists to accurately determine where incoming air has originated from; thereby allowing them to determine (even if the air modifies somewhat positively (average air temperature warms) or negative (average air temperature cools) to some degree) where the air is coming from. By being able to know this information, operational forecasters can more effectively anticipate how the forecast will evolve over some reasonable period of time which can improve the likelihood of them having less forecast error. This is especially important for winter-time precipitation forecasts where even a slight change in the lower/mid-level atmospheric temperatures are a critical component of anticipating variable changes in precipitation type.
As shown in the graphic above (courtesy of the National Weather Service office in Taunton, Massachusetts), you can clearly see how the starting point of these ensemble backward air parcel trajectories have their respective origins in far northern Canada. Though it is imperative to acknowledge the fact that these air parcels do in fact have their initial origins in the southern periphery of the Arctic Circle. That pays dividends to know in the operational sector since through the application of basic mathematical equations, operational forecasters can more accurately build their upcoming forecast for this coming weekend!
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©2016 Meteorologist Jordan Rabinowitz