Because the Mt Washington observatory says so!
Spencer, in response to your earlier post, I am not a professional meteorologist. I have taken a number of college courses, and it is a major hobby of mine. When I post regarding storms, I always try to state what professionals are forecasting, not my personal opinions. I check 4 major weather models, the three Boston stations, WMUR, the Mt. Washington Obs site, and a few others, and then try to form my own opinion. I share my opinions with family and friends, but don't post it on the internet. Whenever possible, I do provide links to the professional sites.
I hope that no one is using these posts as there only weather source. That being said, the info that is posted is generally pretty usefull.
I contribute to these threads as I can not count the times that I have run into experienced hikers on the trails and say something like, "Good thing were getting a foot of snow tonight", only to hear in reply "Oh, is going to snow?"
Besides, I like computers, predictive modeling, and talking about the weather!