Climographs in Maryland, 1991-2020

Weather and climate are closely related, but they are not the same. Weather represents the state of the atmosphere (temperature, precipitation, etc.) at any given time. On the other hand, climate refers to the time average of the weather elements when the average is over long periods. If the average period is long enough, we can start to characterize the climate of a particular region.

It is customary to follow the World Meteorological Organization (WMO) recommendation and use 30 years for the average. The 30-year averaged weather data is traditionally known as Climate Normal (Kunkel and Court 1990), which is updated every ten years (WMO 2017). Establishing a climate normal or climatology is important as it allows one to compare a specific day, month, season, or even another normal period with the current normal. Such comparisons characterize anomalous weather and climate conditions, climate variability and change, and help define extreme weather and climate events (Arguez et al. 2012). The current climate normal, or just the climatology, is defined for 1991‒2020.

Maryland has a varied geography. The Allegheny and Blue Ridge mountains to the west, the Piedmont Plateau in the center, the Chesapeake Bay, and the Atlantic Coastal Plain to the east. The range of physiographic features and the state’s eastern placement within the expansive North American continent contribute to a comparatively wide range of climatic conditions. Thus, it is expected that the climate over the counties in the south and close to the Bay be different to the climate of the counties over the mountains in the west or farther to the north. A traditional tool in Climatology used to objectively characterize the climate of a region is the climograph.

A climograph is a graphical summary of the climate of a region through the display of the monthly annual cycle of temperature and precipitation. The following are clickable graphics that will display the climographs of the state, climate divisions, counties and Baltimore City.