The jet stream has taken a sharp plunge south from Canada across the eastern third of the country. This jet stream dip is accompanied by a chilly, expansive and very strong area of high pressure at the surface that can be traced back to the Arctic. The barometric pressure was as high as 1048.5 millibars (30.90 inches of mercury) at Lincoln, Neb., early Tuesday morning.
This pattern change is leading to a widespread area of well-below-average temperatures.
Source: The Weather Channel