In my "ignore winter until it gets the hint" move (which is strikingly similar to how I end relationships), I've decided to stop believing that the white stuff that is all over the place is snow.
Marshmallow left over from a second Stay Puft Marshmallow Man attack. And this time it was a bigger Marshmallow Man. We're talking at least 1000 feet tall, rather than 100 feet. That's why there's so much! And why it's all over the country!
You see, a Gozer worshipping cult has been growing in strength across the Midwest and Eastern seaboard. And when this cult, mostly made up of millennials, managed to bring Gozer back this time, they just automatically assumed that his physical form was of the Stay-Puft Marshmallow Man, as that is the form they all know he took in 1984. No one other than the Ghostbusters saw the first form that Gozer took! Therefore, Gozer was a 1000+ foot Marshmallow Man this time.
How did they manage to bring Gozer back? Well, by manipulating Louis Tully into sharing his experiences as the Keymaster. You see, Louis's life has been pretty boring in the past 20 years or so. His stint as a ghostbuster was rather short, as shortly after he donned the uniform, Janine was also trying to convince him to style his hair in a familiar tall and top-heavy style that a certain other ghostbuster styled his hair in. Upon realizing that Janine was unintentionally using his willingness to fill the Egon-shaped hole in her heart, Louis left the ghostbusters and tried to just provide legal and financial advise to the team when needed.
But, eventually, he still wasn't over Janine and when the Ghostbusters shut down in 1991, he felt the need to leave New York entirely. It was then that the cult started watching him. And, eventually, he had reached the point in his life where he was so open and looking for something to fulfill him that the cult swooped in and made him feel like a part of something important again. They told him how amazing he was for being picked to be the Keymaster. How important he was to all of history. How very very special he was. They even started just referring to him as "Vinz", the name of the demon that had taken him over.
Louis lapped it all up, desperate for love. Desperate to be cool. And told them everything.
The cult was lead by the great-grandson of Ivo Shandor, a skilled architect that had studied the designs Ivo had used to make the building used in 1984 and had a few ideas on how to improve upon the original. He built several buildings this time to help create the gateway for Gozer to return, knowing that it would have to be at least 30 years after the first attempt. And in those 30 years, the world kindly suffered so many major problems- wars, economical depression, climate change, and so on- that the cult had no problems recruiting new members that believed that Gozer needed to be summoned to end the world.
And, in early 2014, they summoned him. Big time. As the Stay-Puft Marhsmallow Man. This time it took all the regional versions of the Ghostbusters (instituted by Egon when he re-instated the organization in the late 90s) and every proton pack in existence. It took days, but they defeated him, leaving half the country under a thick coat of marshmallow. Marshmallow that also caused atmospheric disturbances that resulted in extreme cold.
So, there you have it. It's marshmallow. And it's going to suck to clean up when it thaws.