Officially classified by climatologist Wladimir Köppen as having a humid sub-tropical climate, Arkansas is indeed humid, but numerous weather extremes run through the state. Humid sub-tropical is classified generally as a mild climate with a hot summer and no specific dry season. The Köppen classification is correct in that regard, but the state truly has four seasons, and they can all range from fairly mild to incredibly extreme.
The topography of the land and its proximity to the plains to the west and the Gulf of Mexico to the south play a crucial role in its climate and weather. In the United States, warm, moist air travels into the plains from the Gulf of Mexico and interacts with cool, dry air coming over the Rocky Mountains. Strong, low pressure or cold fronts can lift this moisture and quickly produce super cell thunderstorms. The flat terrain of the plains gives the inflow hardly any friction to slow down the rapid growth of these destructive storms. The state of Arkansas is a microcosm of this dynamic, with mountainous terrain in the west and flat prairie to the east.
Arkansas generally has a humid sub-tropical climate, which borders on humid continental across some of the northern highland areas. The state is close enough to the Gulf of Mexico for the warm, large body of water to be the main weather influence in the state. Hot, humid summers and mild, slightly drier winters are the norm. Fall brings the first tastes of cooler air arriving in September, but it has been ninety degrees as late as November 17. Lasting cold usually arrives by the start of November.
Winters can be harsh for brief amounts of time. Snow usually brings the state to a slow down, but an ice storm can shut it down completely. Minor ice accumulations happen somewhere in the state almost every winter, while major ice storms happen every five to ten years and can be extremely devastating. Cold but shallow air masses allow warmer, moisture-laden air to move up and over the cold air, producing freezing rain. This happens often because of the state’s proximity to the Gulf of Mexico.
The first hints of spring arrive by early March, with most vegetation reaching full bloom by early April. Winter can still cause damage to crops in April, as the latest “last freeze” of the season has happened as far into spring as May 13. Spring is also the primary severe weather season in the state. Floods and severe thunderstorms are the primary threats from March to May.
Shale is a sedimentary rock that is often associated with oil deposits. This is due in part to the tiny and very fine grains that make up shale. As the sediments are compacted, organic matter is trapped by the particles of clay and silt.
Later, as sedimentation continues and the layers are buried farther underground, the heat and pressure convert some of the organic material into oil. While much of the gas escapes the porous shales, some also remains trapped in the rock layer.
