Thanks to both cloud cover and a modified Arctic air mass that moved in earlier this week, Wednesday definitely had that wintry feel, which has been missing this month so far, with a high of only 39 at Blacksburg and 44 at Roanoke. A shield of rain worked into central North Carolina on the backside of wave of low pressure near the coast, and there were some reports of sleet. The next couple of mornings will be typically chilly for this time of year, with 20s to low 30s common, but afternoon highs will begin gradually climbing back into the 50s, possibly scraping 60 by Sunday. A new cold front, pulled by a low to our northwest over the Great Lakes, will bring a chance of showers late Sunday and Monday, and shave some degrees off the temperatures again.
Already getting more attention than the late Sunday/Monday front and rain chance is a potential storm system that could affect much of the Eastern U.S. in the Tuesday to Thursday timeframe. A few runs of the Global Forecast System (GFS) model in the past few days gave Southwest Virginia snow fans a bit of excitement in depicting a wet low throwing deep moisture into cold air over our region. The European model, at least for one run, seemed to concur, but both models are now less bullish about snowing us on the third anniversary of our Dec. 18-19, 2009, snowstorm. One key difference in the models showing snow for us next week and not showing snow is whether or not a low is located near Newfoundland. Often called the “50-50″ low, because of its position near 50 degrees latitude and 50 degrees longitude, this feature can act as something of a traffic cop and force a storm behind it to take a southerly track near the Gulf of Mexico (scooping up moisture) and then up the East Coast (positioned perfectly for cold to pour behind it.) Another variation is just that the deep Arctic air is a little slower arriving on those models showing no snow. Today’s 12Z run of the Euro, linked here and pictured at left, actually shows a near-perfect track for a potential snowmaker in Southwest Virginia, but it lacks the deep cold air to pull into it to make it snow — it would be windy rainstorm, if something similar to this verified. Unlike with Hurricane/Superstorm Sandy, when the European model locked onto a storm track that turned out to be very close to correct 8 days beforehand, there continues to be some back and forth on the evolution of the storm, whether it will develop near the Gulf Coast and move up the East Coast, or move somewhere inland and then re-develop on the East Coast. The overall pattern, with minimal or misplaced (too far to the east) blocking high pressure in the North Atlantic and the continued PNA-negative pattern of low-pressure dominating in the Pacific Northwest, leans toward a more inland path, perhaps even directly overhead. This would have some potential to bring a much-needed soaking rain to our region to ease the very dry conditions that have developed, but there is also some chance that our region is caught in the gap between the inland storm and a re-forming coastal storm, and we wouldn’t even get much rain. Whatever happens with rain, snow or neither, it does appear likely that we get a substantial surge of cold air for the latter half of next week behind the storm. So take advantage of another fairly mild weekend before things change.
If nothing else, it is certainly the most interesting weather feature we’ve had to monitor in quite a while, and is the first of the actual winter (using the meteorological calendar that started it on Dec. 1) that has at least some chance of being wintry and/or dumping significant and much-needed rainfall. Right now, I am NOT expecting a significant winter storm to come out of this for Southwest Virginia, and I’m scratching my head a little even about the rain potential. Many folks will probably see some snowflakes after it goes by when the cold, northwest winds blow over the mountains, as we typically do, with little or no accumulation in most locations. And it may set the stage for more cold outbreaks and winter precipitation potential as we approach Christmas. We’ll see what exactly this one does before getting too deeply into that.