DETROIT (AP) -- First comes more snow to Michigan, then the freeze. Well, a deeper freeze.
The National Weather Service says winter storm warnings go into effect in Saturday evening in southwestern Michigan and Sunday's early morning hours in the southeastern region.
Much of the southern portion of the state will be blanketed with anywhere from six inches to nearly a foot of snow by late Sunday. Meteorologist Dan Thompson of the weather service's office in Oakland County's White Lake Township says a temperature plunge will immediately follow that sends the thermometer to well below zero on Monday night.
The so-called polar vortex is caused by a counterclockwise-rotating pool of cold, dense air.
A relative warm-up comes later in the week, when temperatures will reach the high 20s.