Climate is the summary of weather conditions for a region over a long period of time. There is a difference between weather and climate; climate is an estimation of long term data, while weather is the current atmospheric condition of the area. It is affected by the exchange of energy and moisture in the atmosphere with relation to the earth. Temperature and precipitation are the major determining factors of a region's climate. The Battlefield's temperate climate results from a collection of global weather patterns and features of nearby landscapes. The park's proximity to the Chesapeake Bay and the Blue Ridge Mountains greatly impacts the climate of the area.
Summers at Manassas National Battlefield are warm and humid while winters are relatively mild. Generally pleasant weather prevails in spring and autumn. Mean annual temperature is about 55 degrees (F) and ranges from 42 to 65. The coldest period, when minimum temperatures average 21 degrees, occurs in late January. The seasonal snowfall is nearly 24 inches but varies greatly from season to season. Snowfalls of four inches or more occur only twice each winter on average. The warmest period, when mean maximum temperature may reach 88 degrees, occurs in the last half of July. Annual precipitation has ranged from about 25 inches to more than 55 inches. Rainfalls of over 10 inches in a 24-hour period have been recorded during the passage of tropical storms. Accumulations of over 20 inches from a single storm are extremely rare. Prevailing winds are from the south except during the winter months when they are from the northwest with the highest average wind speed occurring in March.