Now that Sandy--the storm itself--is behind us, we can start to ask questions about where a storm like this came from and whether it will happen again. To get a handle on how, exactly, Sandy was created, watch this timelapse animation, from the National Oceanic and Atmospheric Administration’s GOES-13 satellite, which shows how the interaction of several weather events created the nightmare storm.
You can see the whorl of the hurricane rise up from the Caribbean and spread over the mid-Atlantic. But then, instead of heading out to see, as most storms do as they roll northward, Sandy became trapped between a "stationary cold front over the Appalachians and a static high pressure air mass over maritime Canada." Denied a route to the North or East, it headed ashore. From NASA’s website:
The Canadian air mass blocked the storm from moving farther northeast. Instead, the joint dynamics (a north-going jet along the stationary front and easterly winds circulating around the south side of the Canadian high) amplified Sandy and drove it westward into the mid-Atlantic states.
Sandy didn’t officially peter out until 5 p.m. Eastern yesterday, when NOAA announced there was no longer any "discernible surface circulation." The hurricane, which had covered 2 million square miles and caused damage in 17 states, was now just a small band of low pressure over Western Pennsylvania. Almost like nothing ever happened. Until the next time.