Baltimore has a humid subtropical climate with hot, humid summers and cool winters moderated by the nearby Chesapeake Bay. At Baltimore-Washington International Airport, the 1991-2020 reference averages range from a daily high of 43°F (6°C) in Jan to 89°F (32°C) in Jul. Monthly precipitation averages sum to 45.0 inches (1143 mm) per year.
Spring warms quickly, with thunderstorm chances increasing through May. Summer is hot and humid, with heat indices near 100°F and afternoon storms, while bay breezes nudge shoreline temperatures. Late summer can bring tropical remnants and tidal flooding around the harbor. Fall is crisp and reliably pleasant. Winter varies wildly year to year, with the rain-snow line often wobbling right along the I-95 corridor.