Latest on the Impending Winter Storm in the East 12/19-20, 2009

So no one on here really cares about the meteorology behind the storm. Y'all just want to know how much in my backyard. I'll try and make it simple. Some might argue I shouldn't care either. It's going to be 70-75 and sunny all weekend here. But, hey, when you get no weather and you love weather, you miss weather. I'll live vicariously.

This is a very complex setup. Cold air has drained in. You have major atmospheric blocking taking place out West, over Greenland, in the Arctic. You have energy driving in from the west. You have a monstrosity of moisture lifting north from the Gulf. It's what I call a powder keg setup, because something is going to explode. This may very well be what is needed to explode.

The philosophy early on was that the moisture from the Gulf was going to slide into the Carolinas and Virginia. Then that second batch of energy would follow suit and bring some snow showers north of Richmond, VA into PA. That never really entirely made sense, but it's what the models were saying...so other than screaming "Potential!" there's been no way to really hammer that someone is going to get rocked.

So there are a number of different "models" we use. Like the runway, some are hotter than others. There's the NAM (only forecasts 3.5 days, but is a higher resolution). There's the GFS (main American computer model, that forecasts out 16 days...generally useful in the first couple days (though that's debatable) and then can just be used to identify trends (hotter, colder, wetter, etc.) in the longer range. There's the European model (similar to the GFS, but generally superior). And then there's a bunch of others. A Canadian, the UKMET (British model), and a bunch of high resolution, short-range models that we use as well.

The NAM was the first to bite and crushed areas south of the Mason-Dixon line with heavy snow. The NAM edged northward with time. The European model this morning absolutely blasted DC to Boston. All the models are generally trending toward one another now that we're close in (though the Euro threw a curve ball tonight, which I don't trust). So we can say a few things.

- Storm will spread moisture/snow into the Mid-Atlantic (south of Philly) Saturday before sunrise.

- Snow should develop across South NJ and Philly through Saturday morning.

- Snow will struggle to get north of I-195 through the day Saturday.

- As the storm system undergoes rapid cyclogenesis (strengthens rapidly) off the coast of MD/DE/NJ, heavy snow will rapidly explode and spread north through NJ, eastern PA, NYC, CT, Long Island, RI and MA.

- That should occur Saturday evening or before Midnight.

- Heavy snow will linger through the night Saturday and wind down from DC through NYC from 7 AM to 4 PM Sunday. Snow may not end til Monday morning around sunrise in Boston.

So how much? Here you go!

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