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The city of Dallas has a humid, hot climate and is often prone to storms (Köppen climate classification Cfa), though it is located in a region that also tends to receive warm, dry winds from the north and west in the summer, bringing temperatures about at times and heat-humidity indexes soaring to as high as . A couple of times each year, warm and humid air from the south overrides cold, dry air, leading to freezing rain, which often causes major disruptions in the city if the roads and highways become slick. On the other hand, daytime highs above are not unusual during the winter season. Extremes in weather are more readily seen in Dallas and Texas as a whole than along the Pacific and Atlantic coasts, due to the state's location in the interior of the United States. Spring and autumn bring pleasant weather to the area. Vibrant wildflowers (such as the bluebonnet, Indian paintbrush and other flora) bloom in spring and are planted around the highways throughout Texas.〔(TXDOT ) - (Wildflower and Fall Foliage ). Retrieved on 17 April 2007.〕 Springtime weather can be quite volatile, but temperatures themselves are mild. The weather in Dallas is also generally pleasant between late September and early December, and unlike springtime, major storms rarely form in the area. In the spring, cool fronts moving south from Canada collide with warm, humid air streaming in from the Gulf Coast. When these fronts meet over north central Texas, severe thunderstorms are generated with spectacular lightning shows, torrents of rain, hail, and occasionally, tornadoes. Over time, tornadoes have perhaps been the biggest natural threat to the city. Summers are hot, with temperatures approaching those of desert and semidesert locations of similar latitude. Heat waves can be severe. The U.S. Department of Agriculture places Dallas in Plant Hardiness Zone 8a.〔(USNA ) - (USDA ) (Plant Hardiness Zone Map: South-Midwest US ). Retrieved on 13 June 2006.〕 According to the American Lung Association, Dallas has the 12th highest ozone air pollution in the nation, ranking it behind Los Angeles and Houston.〔(Lungusa.com ). Retrieved on 2 March 2006.〕 30% of the air pollution in Dallas, and the Metroplex in general, comes from the three cement plants in the town of Midlothian, as well concrete installations in neighboring Ellis County,〔(Downwindersatrisk.org ) - (Pollution in Midlothian ). Retrieved on 17 April 2006.〕 but the foremost contributor to air pollution in Dallas is exhaust from automobiles. Due to the area's spread-out nature and high amount of urban sprawl, automobiles are the only viable mode of transportation for many residents in the metropolitan area. The city's all-time recorded high temperature is during the Heat Wave of 1980, while the all-time recorded low is in 1980 and 1899 respectively.〔(【引用サイトリンク】title=Dallas/Fort Worth - Normal, Means, and Extremes )〕 The average daily low in Dallas is and the average daily high in Dallas is . Dallas receives approximately of equivalent rain per year. == Volatile weather == 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Climate of Dallas」の詳細全文を読む スポンサード リンク
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