Sorry I saw that its a 2000 after I hit post.
Well this falls into the category, if you look at the back of your sunvisor you will read all about how your Explorer is a truck and handles differently then a car, etc etc.....
So thats it, its the nature of the beast. If you have a limited slip rear axle that could make things worse, but basically just know that your truck will do this, and use caution.
It may not be a bad idea to spend some time in a vacant lot getting to know the handling of your truck in different situations.....
Heck my truck will actually lift a front tire if I turn fast and hard enough......

I have gotten the BII sideways a hudred times, three times were not on purpose, two of those on ice. Once the rear kicks out, it doesnt take much to get it all the way around. Now my BII is ALOT different from your 2000, but anything with a higher center of gravity (read SUV) and a shorter wheelbase will handle like this.
Best thing you can do is just be familiar with the handling characteristics of your truck, even if it means practicing in a vacant lot, so you will be better prepared to react in the future.
Nothing is scarier then losing control of the vehicle, I did a 360 ALMOST into oncoming traffic at about 40 MPH in my lifted BII on ICE. I was able to stop in the center divider lane facing the wrong way and not go into oncoming traffic......only because I had been sidways before in my truck, and I have learned how to feather the gas and brakes to bring it back into control.