Kevin Myatt is The Roanoke Times' weather columnist.

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As expected, it was a wet Christmas, not a white Christmas.

Even if much more cold air had been available, it still probably wouldn't have been a snowy Christmas. Most likely, because of the path of the storm system causing the precipitation, it would have been an icy Christmas instead.

Much hinges on the exact track of a low pressure system, especially in winter, when cold air may be involved.

Our most moisture-laden low pressure systems, originating in or near the Gulf of Mexico, generally move to the northeast, but there are many different paths they can take.

Four possibilities are broadly categorized in the accompanying graphic.

The most simple principle to keep in mind about any of these storm paths is that the warm part of the storm is to the east, or right, of the storm's track, while the cold part is to the west, or left, of the track.

This is because of the counterclockwise circulation of a low pressure system. To the east of it, winds are out of the south and east, drawing warmth and moisture from the Gulf of Mexico and Atlantic Ocean. To the west, winds are out of the west and north, drawing colder air from Canada and the northern United States.

Typically for precipitation to be more wintry in Southwest Virginia, the storm must track to the east of us, so we can be on its cold side.

It gets more complicated when cold-air damming is involved. Cold-air damming is the term applied to the banking of cold air against the east side of the Appalachian Mountains.

When a high pressure system is properly placed in southeast Canada, it drives northeast winds down the East Coast that push cold air southwestward, sometimes as far south as Georgia and Alabama. The cold air presses against the mountains, but generally does not cross them.

When cold-air damming is present, a system moving to the west of us will still draw up warm, moist air from the Gulf of Mexico, but that humid air will overrun a colder dome of air trapped at the surface.

When the banked cold air is above freezing, that results in the dreary, damp, foggy kind of weather we've been experiencing.

If the cold air is more intense and temperatures are below freezing, warm air drawn over cold air often results in sleet and freezing rain.

The Christmas Day storm was an "Appalachian runner." The low formed in the Gulf of Mexico and then followed a path to the northeast generally along the Appalachian Mountains.

We have had some big ice storms out of Appalachian runners in the past.

Other times, when the cold air is especially deep, we've had those winter storms where we start with several hours of snow, then change to sleet, then to freezing rain. Walking or driving is like breaking through ceramic.

But this time, the cold air wasn't deep enough. There was a bit of cold air damming, but only enough to keep surface temperatures in the upper 30s and low 40s. Enough to make it dreary, but not icy.

Most of the winter storms we've seen so far this season have been of the "Lakes cutter" variety, or even farther west as a true Plains storm. As a result, it's been a big season for the Rockies and the central U.S. to see winter storms, but not at all for the eastern U.S.

We are at the time of year when an "inland runner" or "coastal storm" traveling east of us has the potential to manufacture significant snowfall even if the cold air is marginal. So every new storm bears watching to see if its path will go east of us, giving us a winter storm threat.

Until some Arctic air returns, though, even those kind of storms wouldn't have a lot to work with.