Baltimore sits at the head of the Patapsco estuary on Chesapeake Bay in central Maryland, on the fall line between the coastal plain and the Piedmont at approximately 39.29°N, 76.61°W. It has a humid subtropical climate (Köppen Cfa) — with hot, humid summers and cool winters — moderated slightly by the bay.

Summer, from June to August, is hot and humid, with July the warmest month — average highs around 31–32°C — and heatwaves that can exceed 35°C, made stifling by humidity off the Chesapeake. It is the wettest season, with frequent afternoon thunderstorms, and tropical systems occasionally bring torrential rain in late summer.

Winter, from December to February, is cool and variable, with January the coolest month — average highs around 6°C and lows near -3°C. Snow falls, around 50 cm a year, though totals swing dramatically depending on whether nor'easters track close to the coast; freezing rain is a recurring hazard on the fall line.

Baltimore receives around 1,050–1,100 mm of precipitation a year, spread fairly evenly through every month with a summer maximum from thunderstorms and tropical systems. Live rainfall, humidity, and pressure readings for the city are shown in the panels above.

Baltimore sits on the fall line where the coastal plain meets the Piedmont, a boundary that often marks the difference between rain and snow in winter storms — the same storm can drop heavy snow on the city's northern suburbs and cold rain on the harbour a few kilometres south.

To follow any single measurement in Baltimore more closely, use our live instruments: the online barometer for atmospheric pressure, the thermometer for temperature, the hygrometer for humidity, the anemometer for wind speed, the wind vane for wind direction, and the rain gauge for rainfall.