Janus is almost upon us, and it’s looking like the big storm of Winter 2014. At least, I hope we don’t get one bigger than this. Tuesday will be an interesting day for the MidAtlantic states.

By the time Janus is finished on Wednesday, the most heavily populated region of the U.S. will be snow-covered, with millions of people affected. Snow from at least as far south as Richmond, maybe even North Carolina, to north of Boston.

All day Monday, forecasters were busy charting the course of the big chill coming south from Canada. It was snowing in Chicago Monday night, with a possibility of heavier “lake effect” snow east and south of Chicago and into northern Indiana.

But the main event begins Tuesday morning, far southeast of The Windy City, as the big cold front pushes through West Virginia, Pennsylvania, Maryland and Virginia. A major low-pressure system is expected to form over the Atlantic, not far offshore.

That low-pressure system will mix lots of moisture from the ocean into the freezing Canadian air, creating the biggest snowstorm in at least three years for the Washington, D.C., region. The snowfall is expected to intensify through the afternoon and evening as Janus storms straight up the East Coast, involving Baltimore, Philadelphia, all of New Jersey and New York City.

Four to six inches of snow are predicted for Northern Virginia and the Nation’s Capital. Make that four to eight inches north of Washington, from Baltimore to New York City. Long Island is expected to be hit harder than NYC, and the worst conditions are expected in the greater Boston and Cape Cod area.

But this is a big and powerful winter storm, with a combination of high winds, frigid temperatures, and an unlimited supply of moisture off the Atlantic. Forecasters are warning that local areas from D.C. on north might get as much as a foot of snow. Heaviest accumulations are likely from Long Island to Boston.

For a worst-case scenario, see http://firsthandweather.com, where blogger Matthew Holliday doesn’t hesitate to use the B-word, as in Blizzard. In Maryland, the storm looks to me more like a Nor’easter than a blizzard. But Nor’easters can be plenty fierce along the Atlantic coast. The good news is that the storm should be fast-moving, not hanging around for three days and inflicting damage. Matthew Holliday warns us that another big winter storm out of Canada is possible next week, the last week of January. Let’s not think about February.

In the Central Maryland suburbs north of D.C., the contrast from Monday, with high temperatures in the low 50s, to Tuesday, with a high of maybe 27 degrees, will be sharp. And sharper still when you factor in the wind chill. We’re talking storm winds in the 15-25 mph range in Maryland. The freezing temps will hang around all week. I doubt we’ll see 32 degrees before Saturday. The cold will be far more bitter, even dangerous, across the northern tier, from Minnesota and Wisconsin to New England.

In Montgomery County, north of Washington, the temperature has fallen nearly 20 degrees from 4 p.m. Monday to midnight. Heaviest snow is expected in late afternoon and evening. By Wednesday, the sun may be out, but it will remain below 30 degrees Wednesday and Thursday. No quick melting for this snow.

Many school systems in the Maryland and Virginia suburbs have already announced they’ll be closed Tuesday. Check WTOP radio or its Web site for specific closings. In the Baltimore area, check WBAL radio. Or check the Web page of your local public schools.

I haven’t heard anything yet about plans for the D.C. public schools or federal employees.

Good luck, stay warm, and remember to bring your animals inside from the storm. What are conditions like in your state or locality? You can leave comments below.

— John Hayden