Remember when last December, a bout of cold weather crushed the US economy for the next 3 months, and subtracted about $100 billion from trendline growth, and when one after another economist (who were then predicting the yield on the 10 Year would "greatly rotate" to 4% by right about now, and who expected the US economy to have reached escape velocity in the second half only to see a 2014 GDP trendline as follows Q2: 4.6%, Q3: 3.5% (soon to be reviser lower), and Q4 now estimated just about 2.0%) blamed the then -3.0% GDP print on snow in the winter? Well here comes round two, because as CBS reports, "prepare for an invasion from the north. A blast of polar air is about to send temperatures plunging in the heart of America." The polar vortex is back, and this time it means even less business: A mass of whirling cold air will dip southward this weekend, sending the mercury plunging. As the cold air moves south and east, it has the potential to affect as many as 243 million people with wind chills in the single digits in some places and snow.