October Superstorm. Lowest Pressure On Record For The USA. Welcome to the Land of 10,000 Weather Extremes. Yesterday a rapidly intensifying storm, a “bomb”, spun up directly over the MN Arrowhead, around mid afternoon a central pressure of 953 millibars was observed near Orr. That’s 28.14″ of mercury. Bigfork, MN reported 955 mb, about 28.22″ of mercury. The final (official) number may be closer to 28.20-28.22″, but at some point the number becomes academic. What is pretty much certain is that Tuesday’s incredible storm marks a new record for the lowest atmospheric pressure ever observed over the continental USA. That’s a lower air pressure than most hurricanes, which is hard to fathom. [Ed. Note - this record refers to storm forming over the interior U.S.]
How did this happen, especially coming after 4 dry, mild, unusually sunny & quiet weeks/row? Generally speaking, the larger the “baroclinicity” (the north-south temperature contrats across N. America) the greater the potential for an epic storm to develop. Yesterday all the ingredients converged over Minnesota, an unusually powerful jet stream core (blowing at close to 200 mph 5-8 miles overhead). The approach of a “jet streak” aloft caused a partial vacuum to form over the MN Arrowhead, air rushing into this low pressure system accelerated to speeds as high as 60 mph, downing trees and powerlines, cutting off power to WeatherNation in Excelsior for a time during the evening hours.