Philadelphia is great to visit any time, although given the city's seasonal popularity and the constant flow of conventions, you'll find the best deals in the fall and winter. Concert and museum seasons run from early October to early June, and July 4th draws a festive crowd to Independence Hall.
The city has four distinct seasons with temperatures ranging from the 90s (30s Celsius) in summer to the 20s (around 0°C) in winter. (Below-zero temperatures normally hit only one out of every four winters.) Summers, the height of tourist season, can get swelteringly humid. In the fall, the weather becomes drier. Spring temperatures are variable; count on comfortable breezes. I like late September and late May best.
Banks, government offices, post offices, and many stores, restaurants, and museums are closed on the following legal national holidays: January 1 (New Year's Day), the third Monday in January (Martin Luther King, Jr., Day), the third Monday in February (Presidents' Day), the last Monday in May (Memorial Day), July 4th (Independence Day), the first Monday in September (Labor Day), the second Monday in October (Columbus Day), November 11 (Veterans Day/Armistice Day), the fourth Thursday in November (Thanksgiving Day), and December 25 (Christmas). The Tuesday after the first Monday in November is Election Day, a federal government holiday in presidential-election years (held every 4 years, and next in 2012).
Note: This information was accurate when it was published, but can change without notice. Please be sure to confirm all rates and details directly with the companies in question before planning your trip.