AccuWeather.com

By Alex Sosnowski, Expert Senior Meteorologist

Feb 1, 2011; 6:25 AM ET

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For more details on the storm and how it will affect the Midwest, click on this video.

Both a major blizzard and an ice storm will unfold across a large portion of the central Plains and Midwest today and tonight. Arctic air will charge in during the storm in some areas and after the storm in others, leading to additional concerns.

For some locations, the storm may be a two-day event or much longer than a typical winter storm. It could even end up being one of Chicago's biggest snowstorms in history.

An area of snow and ice that developed on Monday evening across the southern Plains, even with embedded lightning and thunder, forewarns a dire situation for millions of people.

Immobilizing Blizzard

Blizzard conditions will target areas from Wichita Falls to Oklahoma City, Wichita, Kansas City and Chicago today and tonight with blinding snow and extensive blowing and drifting. The snow could fall fast enough to strand motorists on roadways.

For a map of expected snow accumulations, visit the AccuWeather.com Winter Weather Center

State of emergencies have already been declared in Oklahoma and Missouri, barring non-essential travel. Additional declarations are possible later today as conditions deteriorate.

Airline passengers may be stuck at airports for an extended stay as some of these facilities may be forced to ground many flights.

While areas from Omaha to Minneapolis will escape the heaviest snow, fierce cold rushing in behind the storm will make for dangerous conditions to be outdoors or to travel for a time.

Already, snow that fell in the Minneapolis area on Monday has been responsible for a number of automobile accidents.

The storm will hit the Chicagoland area very hard with from 1 to perhaps 2 feet of snow and an all-out blizzard. Detroit will share in the blizzard with the potential for up to 18 inches.

Major Ice Storm

An ice storm will be another serious aspect of the storm from part of the southern Plains to the Ohio Valley, with the heaviest icing evolving from west to east through the day today.

Freezing rain will stretch from portions of southern and central Ohio westward to southern Illinois and southern Missouri into the southern Plains. In some areas, the glaze of ice and sleet may exceed 0.25 of an inch. Cities at risk for an ice buildup include Zanesville and Columbus, Ohio, Indianapolis, Ind., and Decatur, Ill.

The possibility exists that some areas along that zone could have over a half-inch of ice buildup.

Where ice accrues over 0.25 of an inch, there is an elevated risk of power outages due to falling trees and utility lines. With wind speeds expected to increase later tonight and tomorrow, additional damage could leave some without power for days.

Other areas will get ice, too. However, the ice may occur as rain changes to freezing rain and sleet briefly then switches to all snow. This is likely in St Louis and Springfield, Mo., to Tulsa, Okla., where snow will be the big story.

Rapid Freeze-Up

Another possibility for some areas is that snow falls, then melts, then freezes. This is the chain of events that is most likely over the middle Mississippi Valley to the southern Plains.

These areas and others will share in the risk of power outages as the weight of the ice combined with clinging snow will pull down trees and power lines just the same as a pure glaze.

As many experienced motorists know, ice under snow is difficult to drive on. There is no traction on a glaze of ice, no matter what vehicle you are driving whether it is a semi, SUV or subcompact.

Even in areas that get mostly rain from this storm, as temperatures plunge from northwest to southeast in the wake, untreated wet areas will freeze. In areas that get snow, slush will freeze underneath.

The bottom line is a historic storm impacting not only people in the Midwest and in the Plains, but the Northeast where the worst of the storm will strike on Groundhog Day. A severe weather outbreak could also spawn tornadoes in the South.

AccuWeather.com Meteorologist Bill Deger contributed to the content of this story