Get out now while you still have the chance! A blizzard warning has been issued for New York City and much of the tri-state area beginning at midnight Tuesday as Winter Storm Stella threatens to dump as much as 18 inches of snow. Whiteout conditions are expected to make travel extremely dangerous and power outages are likely amid crippling wind gusts of 20 to 40 mph, according to AccuWeather senior meteorologist Tom Kines. New Yorkers stockpile supplies as massive snowstorm looms. “Travel will be poor at best, if not impossible,” Kines told The Post on Monday. “If you have the...