Fall and spring are the most beautiful seasons in New York, with mild temperatures and changing foliage.
Winters (November through March) can be cold and snowy, although they have been less severe in recent years. It is smart to travel to the Catskills during the winter months and take advantage of the great skiing at http://www.windhammountain.com and http://www.huntermtn.com. While in the Catskills, the http://www.catskilllodge.com is a B&B with great reviews in Windham, NY located between Hunter and Windham Mountain.
Summers are hot and humid, and the subway stations can sometimes become unbearably so, but then they always are with all of the people. In the summer Woodstock NY becomes a very attractive little town, there are still many hippies in town and plenty of art, antique and coffee shops to enjoy. You may also enjoy Saratoga raceway in August. This is a very popular destination in August and you should book far in advance!!
