Oklahoma’s geographic location and topography have a critical effect on the state’s climate. Like many plains states, Oklahoma is known for its changeable and varied weather patterns. During the winter it is common for the south and southeast regions to bask in springlike temperatures when as much as 300 mm (12 in) of snow falls in the Panhandle. About four-fifths of Oklahoma outside of the Panhandle is categorized as humid subtropical, with very hot, long summers and moderate short winters. The western portion and the Panhandle are classified as a steppe, where precipitation, typically 250 to 500 mm (10 to 20 in), is the controlling characteristic.
January is usually the coldest month with an average of about 3°C (38°F) and extremes from -33°C (-27°F), the lowest ever recorded, to 33°C (92°F). Summer are long and hot with temperatures in the upper 30°s C (lower 100°s F) common from May until September across the state. The growing season varies from less than 180 days in the western Panhandle to more than 240 days in the southeastern Coastal Plain. Oklahoma occupies a transitional precipitation zone, with a humid east and a semi-arid west. Rainfall averages from 1,270 mm (50 in) in the Ouachita Mountains to just 380 mm (15 in) in the far western Panhandle.
Spring is generally the wettest, but in the west this advantage is offset by the high evaporation rate. Two defining weather phenomena in Oklahoma are drought and tornadoes. Periodic droughts occur particularly in semiarid areas of western Oklahoma, the most famous of which occurred during the Dust Bowl era of the 1930s. The state averages dozens of tornadoes annually, especially during the months of April and May. These destructive storms are embedded in thunderstorms and move from southwest to northeast across the state. "Oklahoma" © Emmanuel BUCHOT, Encarta, Wikipedia
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