Climate classification systems offer a standardized way to describe the general weather characteristics of a region over long periods. Understanding a location’s climate zone is important for various planning activities, including infrastructure development and water management. These classifications provide expectations for seasonal temperature ranges, typical precipitation levels, and general weather behavior. Knowing the climate helps determine which crops will flourish and what kind of heating or cooling demands a building will require.
Arkansas Under the Köppen Climate System
The vast majority of Arkansas falls under the Humid Subtropical climate, designated as Cfa within the Köppen classification system. The “C” indicates a temperate climate where the average temperature of the coldest month remains above 0°C (32°F). The “f” signifies that precipitation is distributed throughout the year with no dry season. The “a” indicates a hot summer, meaning the average temperature of the warmest month exceeds 22°C (71.6°F).
This classification accurately describes the state’s weather, characterized by long, hot, and humid summers. Summer temperatures routinely reach the 80s and 90s degrees Fahrenheit, with high humidity causing the heat index to climb even higher. Winters are generally mild and short. However, they feature significant temperature fluctuations as warm, moist air from the south alternates with cold, dry air masses arriving from the north.
Precipitation is ample year-round, averaging between 40 and 60 inches annually across the state. Rainfall tends to be higher in the southern areas compared to the northern uplands. This distribution of moisture supports the humid designation. The Cfa classification is shared by many of Arkansas’s neighbors, including Tennessee, Louisiana, and parts of Oklahoma, placing the state firmly within the climate type dominant across the southeastern United States.
Defining Planting Zones
While the Köppen system classifies the overall climate, gardeners and farmers use the USDA Plant Hardiness Zone (PHZ) map to determine which perennial plants can survive the winter. This practical classification is based solely on the average annual minimum winter temperature, providing a measure of a plant’s cold tolerance. This is distinct from the Köppen system, which relies on temperature and precipitation averages across all four seasons.
Arkansas is a state of varied growing conditions, spanning several zones. Historically, the state ranged from Zone 6b in the coldest, highest elevations of the northwest to Zone 8a in the warmest southern and eastern regions. With the most recent updates to the USDA map, Arkansas now primarily falls within Zones 7a through 8b. Zone 7a indicates an average minimum temperature range of 0°F to 5°F. Zone 8b, found in the far south, reflects a warmer range of 15°F to 20°F.
The majority of the state is covered by Zones 7b and 8a, which translates to average annual minimum temperatures between 5°F and 15°F. These zones guide gardeners in selecting perennial shrubs, trees, and flowers that are reliably hardy for their specific location. For example, a plant rated for Zone 8 will likely struggle to survive the typical winter lows experienced in Zone 7a without extra protection. The distribution of these zones across Arkansas reflects the underlying physical geography of the state.
Geographic Influences on Climate Variation
Arkansas’s specific climate characteristics and planting zone variations are primarily dictated by two main geographic factors: proximity to the Gulf of Mexico and internal topography. The Gulf of Mexico, located to the south, serves as the predominant source of moisture and heat defining the state’s Humid Subtropical climate. Air masses moving north from the Gulf carry water vapor, contributing to high humidity and significant year-round precipitation. This marine influence keeps winter temperatures milder than inland continental locations.
The state’s varied landscape, particularly the mountainous regions in the northwest, introduces local climate variations. The Ozark and Ouachita Mountains feature higher elevations, which are directly responsible for the lower average minimum winter temperatures found in those areas. This elevation effect currently keeps the northwestern part of the state in the cooler portions of Zone 7.
In contrast, the eastern and southern parts of Arkansas, encompassing the Gulf Coastal Plain and the Mississippi Alluvial Plain, are much flatter and lower in elevation. This lowland topography allows Gulf air to move freely, resulting in warmer winter minimums and a longer growing season. This corresponds to the warmer Zones 8a and 8b. The topography creates a distinct north-to-south gradient in cold tolerance across the state.