Seth Wenig/AP

The devastating effects of the rare October snow storm that rocked the Northeast over the weekend resulted from the unusual mix of wet, heavy snow and leafy trees.

“The combination of things was a perfect storm,” said Dena Libner, spokeswoman for the Central Park Conservancy.  ”The trees were unusually green and the presence of leaves served to support a lot more snow, causing a lot more damage.”

The storm left thousands of roads littered with debris and millions of people without power. States of emergency have been declared in Massachusetts, Connecticut, New Jersey and parts of New York.

According to Libner, Central Park park may lose 1,000 trees because of the storm.

“This was more devastating than the tornado in August 2009 that hit the north end of the park and took out 500 trees,” she said.

Tree branches cover the roads in northern New Jersey, and downed power lines are draped across many streets. Traffic lights in many northern parts of the state remain out, and residents that are still without power are congregating over their laptops at coffee shops that still have heat.

“This season we’ve had a warm fall and a lot of moisture, even though the days have been changing things are delayed a little bit,” Mark Fisher, director of horticulture at the Brooklyn Botanic Garden, told ABC News. “The leaves are holding so much moisture, and when the snow accumulates on the leaves it can be very destructive.”

In Bloomfield, N.J., the storm even managed to short-circuit Halloween.

“Halloween has been rescheduled for Friday Nov. 4, 2011,” a robocall alerted residents.

(ABC News’ Linsey Davis and Olivia Katrandjian contributed to this report.)