parts of the province experience higher rainfall and lower evaporation rates caused by cooler summer temperatures. The south and east-central portions are prone to drought-like conditions sometimes persisting for several years, although even these areas can receive heavy precipitation, sometimes resulting in flooding. In the winter, the Alberta clipper, a type of intense, fast-moving winter storm that generally forms over or near the province and, pushed with great speed by the continental polar jetstream, descends over the rest of southern Canada and the northern tier of the United States. In southwestern Alberta, the cold winters are frequently interrupted by warm, dry Chinook winds blowing from the mountains, which can propel temperatures upward from frigid conditions to well above the freezing point in a very short period. During one Chinook recorded at Pincher Creek, temperatures soared from in just one hour. The region around Lethbridge has the most Chinooks, averaging 30 to 35 Chinook days per year. Calgary has a 56% chance of a white Christmas, while Edmonton has an 86% chance. After Saskatchewan, Alberta experiences the most tornadoes in Canada with an average of 15 verified per year. Thunderstorms, some of them severe, are frequent in the summer, especially in central and southern Alberta. The region surrounding the Calgary–Edmonton Corridor is notable for having the highest frequency of hail in Canada, which is caused by orographic lifting from the nearby Rocky Mountains, enhancing the updraft/downdraft cycle necessary for the formation of hail. Ecology Flora In central and northern Alberta the arrival of spring is marked by the early flowering of the prairie crocus (Pulsatilla nuttalliana) anemone; this member of the buttercup family has been recorded flowering as early as March, though April is the usual month for the general population. Other prairie flora known to flower early are the golden bean (Thermopsis rhombifolia) and wild rose (Rosa acicularis). Members of the sunflower (Helianthus) family blossom on the prairie in the summer months between July and September. The southern and east central parts of Alberta are covered by short prairie grass, which dries up as summer lengthens, to be replaced by hardy perennials such as the prairie coneflower (Ratibida), fleabane, and sage (Artemisia). Both yellow and white sweet clover (Melilotus) can be found throughout the southern and central areas of the province. The trees in the parkland region of the province grow in clumps and belts on the hillsides. These are