Winter can be spotty in NJ. In some past winters, I've used race skis at High Point until mid March; other years winter ends pretty early. When it snows, use your imagination and you'll find a place to ski right in your neighborhood. If we're blessed with a blizzard or two during winter, it can be pretty amusing to tour your town before the streets are plowed.
The following are places I like to ski, both in NJ and within a reasonable driving distance. It is by no means exhaustive. The NJ Division of Parks and Forestry seems to list every park in NJ as a place to go skiing. Know that you'll be setting your own tracks when you go to these places: to my knowledge, none are groomed. Most of them should be pretty interesting, however, I feel that some are probably better suited for snowshoeing. Ken Roberts has a comprehensive listing of options in New York State, many in the lower Hudson Valley.
High Point Cross Country Ski Center. Located in High Point State Park. Good views from the appropriately named Scenic View trail, and the Cedar Swamp. High Point offers rentals, lessons and food service. The grooming is good and, if necessary, they can cover 2 km of trails with manmade snow. Due to the elevation, they often have snow when most of the Garden State is green. Accurate condition reports at (973)702-1222.
Jockey Hollow National Park, Morristown. Lots of rolling trails including a couple of exciting downhills. There needs to be a good base of snow to cover rocks and roots on the trails. Jockey Hollow connects to Lewis Morris County County Park, offering a wide variety of trails when the weather is good.
Freedom Park, Randolph. Located on Millbrook Road. Developed in 2001, this park has a network of gravel-covered bike paths that go on both sides of Millbrook Road. Ungroomed, but easy to follow. You do run the risk of punching down to the gravel if there's not much snow on the ground. Because it's located at a higher elevation than Jockey Hollow, it does get and retain more snow.
Lord Stirling Park, Basking Ridge. Ski around the edges of the Great Swamp, on flat, gentle trails meandering through woodland and meadows.
Fahnestock State Park, near Cold Spring, NY. Fifteen km of fun, interesting trails through mostly hardwood forest. Good grooming. Phone for conditions: 845-225-3998.
Lake Minnewaska State Park, New Paltz, NY. Minnewaska has a lot of sentimental value to me, it's where I learned to ski. On a clear day, you can see New York City from Castle Point. Awosting Road and Castle Point are rolling; there are a couple of crankin' corners and stiff climbs going around the lake. The state bought a grooming machine in 2000; so trail conditions should be much improved after years of neglect. Dress warmly because it can get windy atop the escarpment; there's no lodge or shelter of any sort. Phone 914-255-0752.
Prospect Mountain, Woodford, VT. Just east of Bennington on Rt 9. It's a longish but worthwhile day trip from northern NJ. Good mix of trails in an area which gets lots of snow. Accurate condition reports online or at (802-442-2575) and a very nice lodge.
Notchview Reservation, Windsor MA. About 15 miles east of Pittsfield. 17 km of trails through a mix of hardwood and pine forest, much of which are designated for classic skiing only. Be sure to bring your lunch as food service is primarily hot drinks and energy bars.
Tobyhanna State Park, Tobyhanna, Pa. Located on State Rte 423 just a few minutes off Interstate 380. Main trails are easy terrain; with some narrower, more rolling trails also. To my knowledge, the trails aren't groomed. Relatively high altitude should help them hold snow.