The central and eastern United States have been in the grips of a much colder weather pattern in the second half of January, and conditions this week will be the worst yet.
One instigator for this outbreak of cold air is a displacement of a lobe of the polar vortex to a position over the Great Lakes, according to a wunderground.com blog entry  from Jeff Masters and Bob Henson.
The outbreak this week may be the coldest in more than 20 years in parts of the Midwest and will smash dozens of daily record lows in some areas.
Incredibly, this could be the first January daily record low set in Minneapolis-St. Paul since 1977, according to the National Weather Service.
There could also be a few cities that come close to all-time record lows for any day of the year on Thursday morning.
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