Kevin Myatt is The Roanoke Times' weather columnist.

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• Winter trying again to show up with snow
• We got graupel, but not on official record
• Moisture could get caught up in cold blast
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• Many looking past mild, quiet week toward possibly wild weekend
• Sprinkles or flurries possible Tuesday, but maybe something bigger for the weekend?
• For now, it looks like a quiet, mostly mild week ahead for SW Virginia
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Big-time cold and big-time warmth are butting up against each other this week.

That means there's going to be a big-time rumble.

The rumble has already started, as a strong low-pressure system is winding up in the central U.S. along the dividing line between these air masses. This low has already caused heavy snow in the Pacific Northwest, the Rockies and northern Plains, and snow is likely to develop farther east into the Midwest as well.

To the south, severe thunderstorms will be possible in an arc starting today in Texas. That will stretch as far north and east as the mid-Atlantic, and our area, by Friday.

The formula is painfully simple for severe weather: cold, dry air meeting warm, moist air, with plenty of wind at the surface and aloft to give things a spin.

The greatest threat of truly destructive storms, with tornadoes and strong straight-line winds, will be to our south. But don't be surprised to see a few tree-bending gusts with some rumbles of thunder come Friday morning. Mostly, it will just be a gusty downpour for us as the front barrels into the warmth we've had.

Though we've had a few shots of Arctic-influenced cold from Canada, this is the first major intrusion of Arctic air into the United States this season. It's been building in western Canada and eastern Alaska, over a thickening snowpack, for weeks. Temperatures in some areas have dropped below minus 30.

While it will get sharply colder here come the weekend, ending our second round of Indian summer abruptly, the main punch of this cold air will be southward through the central United States. That's why it might even snow as far south as Oklahoma and Arkansas on the back side of the rain shield.

The cold front will push through, and we will chill out, but the Arctic air will have moderated and the core of it will push more northeast than due east. As a result, temperatures will fall back to near or slightly below normal for a few days rather than going into the deep freeze as might happen if the core of the Arctic air was plunging right at us.

Normal highs this time of year in our area are in the 50s and lows are in the 30s. We'll be a little colder than that by the weekend, then gradually moderating to about right on normal early next week.

I alluded to a slight threat of snow or ice this weekend in my last column. That could still happen if a low-pressure system develops along the front once it passes us and stalls in the western Atlantic back into the eastern Gulf of Mexico.

Currently, there's not much indication of that. It would only take a small ripple, though, to throw back just enough moisture into the cold air to the west to give us such a threat.

Next week, there may be some additional cold fronts moving through to keep the chill fresh.

It will certainly feel a lot more like Christmas than this week, though it probably will not be frigid.

We'll have to keep our eyes peeled to see if there's anything on the horizon that could make it look like a postcard Christmas.