Beijing is renowned for its pleasant springs (65-75 F/18-24 C) and brisk falls (50s F/10-15 C). Summers are hot, with temperatures ranging 85-95 F/30-35 C. Persistent smog can hamper views on particularly hot days. Winters can be extremely cold and dry, especially when Siberian winds blow in from the north; expect frequent temperatures below freezing.
Beijing's rainy season is June-July. Be prepared for dust and sand storms at almost any time, but especially in early spring. September-October—except for the first week of October, which is a national, week-long holiday—is the best time to visit Beijing, hands-down, as blue skies, crisp air and fewer crowds permeate the city.