The winter storm is fast approaching, and we are now in the final hours of preparation before the first snowflakes start falling. You've probably noticed that, for many days in advance, the First Alert forecast team has been billing this storm as a "big one" for our area. Confidence has grown with each passing day that this February Nor'Easter would be the biggest snowfall in the Beltway since the Snowmageddon year of 2009-2010.
Maybe you're thinking, "I've heard this story before! Why would this storm be any different?" Well, there are several factors working in favor of a big snowfall that haven't been in place for previous storms. (Remember "Snowquester"?)
Factor #1: It's very cold now, and it's been consistently cold. High temps have only been in the mid 30s in DC over the past 4 days, and today, we didn't even crack the freezing mark. This means the ground is frozen in most spots, so the first flakes to fall will accumulate, not melt.
Factor #2: The snow starts falling after sunset. This probably comes as no surprise, but it's more difficult to get snow to accumulate when the sun's warmth is trying to penetrate through the clouds.
Factor #3: Just look at the radar! It's already snowing in locations to our south, such as the Carolinas, where snow is a rare event. And they didn't have Factor #2... their snow fell during the daytime! Yet, it is managing to accumulate. This means the air column is cold enough to support snow throughout, and the only thing that would disrupt the snow at this point would be either a warm surface temperature, or a change in the weather pattern. As I mentioned in Factor #1, we know the surface temperatures are cold, so the only possible limiting factor would be a change in the weather pattern.
Factor #4: The forecast model data supports further snowfall development. While the computer model data does show mixed precipitation along the I-95 corridor on Thursday morning, the models are generally showing a snowy air column. That means the temperature stays at or above the freezing mark through a vertical profile of the atmosphere as the snow is falling. This is what it looks like:
Factor #5: Wet snow will fall on top of drier snow. Since the initial snowfall will happen with all the previous factors in place, we will have a sizable accumulation on the ground by the time the snow starts mixing with sleet and/or rain. In fact, rain may never mix in with the snow for locations west of I-95, including the District! So, unlike with previous storm systems, the wet heavy snow will be falling on top of several inches of relatively light snow. This will limit accumulations somewhat, but it means that the snow won't melt altogether.
So, as you can see, there are several reasons that this storm appears to be a bigger snowmaker than any storm we've had since the "Big Year" of 2009-2010!