Roanoke has topped 60 degrees on 9 days in this warm December, and Wednesday has a shot at being the 10th. It may also very well be the last 60-degree day of 2012. Clouds and showers will likely hold it below 60 on Thursday, and then the passage of an Arctic cold front will slap us with blustery winds from the frozen north on Friday. The HPC weather map for Friday shows a double-barrel low to our north and lots of isobars, or lines of equal pressure, packed together. This is a sign of strong winds, blowing in from the northwest in this case. Some 50+ mph gusts will be possible Friday. A winter storm watch has been issued in several West Virginia counties as these winds lifting over the western slopes of the Appalachians sill squeeze out intermittent snow squalls and snow showers from Thursday night through Saturday, with accumulations of 5-plus inches expected especially in higher elevations and along west-facing ridge slopes. Some snowflakes will get carried in the breeze eastward into the New River Valley on Friday — a dusting is possible for anybody that gets under a heavier snow squall for several minutes — and perhaps even into the Roanoke Valley and points east. Temperatures may not get out of the 30s even at Roanoke on Friday, and several mostly dry days of 40s highs/20s lows will follow, likely into Christmas.
Then there is the matter of the after-Christmas storm. The HPC weather map locates its infancy in Louisiana on Christmas. This one could be a headline-maker for much of the country, though there remains much conjecture on its eventual track. Even a track west of us could lead to some wintry precipitation if cold-air damming develops (as the position of some of the highs to the north on this map suggest would be possible). There remains a chance that blocking features in Canada will force the storm much farther south and east and increase our region’s snow threat. Wherever it goes, Arctic air will pour around its back side toward us late next week, so even if it were to go far west and swing in some milder air, it would last only a day or two. We will continue to watch the models play with it the next few days. Anyone traveling for Christmas should be aware that this storm will have the potential to hamper transportation in a wide swath of the nation for a couple or three days after the holiday.