The most-underrated economic factor is still the weather
Economists struggle to predict the impact
There was a great chart on Bloomberg TV just now, it showed how cold spells in the United States have been followed by periods of economic weakness as measured by the Citi Economic Surprise Index.
With a harsh cold bearing down on the US and a big snowstorm in the forecast, this is one to keep in mind. The disappointment tends to peak 1-4 months after the cold.