A massive atmospheric traffic jam will keep chilly air locked in over the Midwest and much of the eastern United States this week, AccuWeather meteorologists say. Forecasters warn that the same pattern set to deliver weather more typical of March rather than May will bring accumulating snow to some spots as well as another round of frosts and freezes to some locations. A pattern in the jet stream, known as an Omega block, shaped like the Greek letter by the same name, will remain over much of No