Weather security

How dangerous (and historic) is the Polar Vortex hitting the Midwest?

...The cold air came, of course, from the Arctic. Events were set in motion several weeks ago, when the normal westerlies circling the Northern Hemisphere midlatitudes at an altitude of 20 to 50 miles, forming what’s called the stratospheric polar vortex, broke down into a disorganized mess. This breakdown, which seems to be more common in recent years, sets the stage for large excursions of warm air toward the pole and cold air toward lower latitudes.

Then, over a week ago, a seemingly inconsequential storm spun up in the Sea of Japan and moved eastward across the Pacific. As it continued spinning, it was able to ingest part of a plume of moisture, an atmospheric river originating in steamy tropical air near the Philippines. The moisture reinvigorated the storm as it was carried aloft and condensed into precipitation. 

Partly because of this invigoration, the downstream jet stream bent northward, then toward the east and then back southward, creating an upper-level ridge. Often, you’ll get a new winter storm forming downstream of such a ridge, in a process called downstream development.