 At the same time, Arctic air was being drawn southward from Canada into the Great Plains, and large amounts of warm tropical air from the Gulf of Mexico were being pulled northward into much of the eastern U.S.The storm was a classic Panhandle Hook which moved from Colorado into Oklahoma before turning northward towards the Upper Midwest.It produced record low barometric pressure readings in the Midwest, with the pressure falling to an estimated 28.38 in (961 mb) just north of the Minnesota border in Canada.