Why the Snow Forecast busted for Baltimore & DC

Even after all of our advances in technology, these things can still happen. The atmosphere is a VERY complex machine! Everything started out just fine, forecast-wise, early Wednesday morning. A nice band of overrunning snow swept across the I-95 corridor before sunrise, and produced 1” to 3” of snow in most areas. After that, things went downhill. The surface area of Low Pressure near Norfolk, VA. , and the Upper Level Low over Central VA became what we call “stacked”. One on top of the other. Now, most of the computer models…the American GFS and the NAM…forecasted this feature to drift to the NE. Instead, it moved South! It only moved about 100 miles South of where it was forecasted, but that’s all it took to mess things up for us weather folks. The heaviest precipitation was circulating around, and close to, the center of the Low…that means the precip became very light around Baltimore and DC. The thermal profile of the atmosphere was set up in the I-95 corridor with a very shallow layer of mild Marine Air near the surface. At about 1500 or 2000 feet up, the temps were below freezing. In the heavy precip bands, the rain/snow is able to “pull” down the cold air to the surface. So basically, when the precip is light, it’s rain at the surface…when it’s heavy, it’s snow. Now, because the computer models thought the storm was going to be 100 miles further North, they were forecasting up to 2 inches of liquid precipitation for Baltimore and DC! The normal conversion rate for liquid to snow is 10 to 1. So, if this were Jan or Feb I would have forecasted 15 to 20 inches of snow! Considering all of the above, I forecasted 5 to 10 inches of snow. Bust! Looking back, the European Model again out forecasted the American Models…even in the short term range. This model typically out performs the GFS and the NAM in the long range, but it’s supposed to be the other way around in the short forecast range (24 to 48 hours out). That’s my story, and I’m sticking to it.