Lanham experiences a humid subtropical climate (Köppen climate classification *Cfa*), typical of the mid-Atlantic region.
Summers are generally hot and highly humid, with average high temperatures in July reaching the upper 80s to low 90s Fahrenheit (31–34°C). Winters are cool to cold, with January lows averaging in the upper 20s (-2°C). Precipitation is well-distributed throughout the year, averaging around 43 inches of rain annually. Snowfall is highly variable but averages about 15 inches per winter, with occasional heavy Nor'easters bringing significant accumulation.
The best times to visit are during the transitional seasons of spring (April to early June) and autumn (September to early November), when temperatures are mild and the local foliage—particularly the cherry blossoms in spring and changing leaves in autumn—is vibrant. Natural disasters are relatively rare, though the area is occasionally subject to severe summer thunderstorms, localized flooding, and the remnants of Atlantic hurricanes.