U.S. natural gas futures spiked to their highest levels in nearly three years as models now show a frigid first half of December across the Lower 48. Several forecasters are also warning of a potential polar-vortex-driven Arctic blast event later this month, which could drive temperatures even lower. Let's begin with an unusual sight (for this time of year) of winter storm alerts across the Northeast on Tuesday morning. ???? WINTER STORM TODAY ????Heavy snow (5-10" expected) in the Interior Northeast & disruptive…