7:45 pm EST Thursday 2-23-12:
New forecasts coming in now and still trending cooler. This means that the secondary low will develop more quickly and reach a greater intensity before being driven off by approaching high pressure that will be building in for Saturday.
Low will approach the area tonight and snow will start at around 5:30am. Little accumulation before dawn but this thin layer will set the stage for more efficient accumulations with heavy snows later. Heavy snow will come with the 2nd low forming roughly 50 miles NE of Boston. This new low will start out fairly strong and will continue to deepen though cyclogenisis is not expected at this point. The new low will start to pull in sufficient cold air starting around 11:00. Warm air advection (which is warm air interacting with cold air usually overtaking it and produces precipitation) will be halted or significantly slowed by this point due to cool air being wrapped in by this point by the secondary low.
East winds brought on by the secondary low passing south of us will draw in warmer air along the coast and we will see a change to sleet possibly mixing with rain.
Snow amounts: Southern York County: 1-3″
Coast north of Portland to 20 miles inland: 3-5″
Inland and foothills: 4-6″