flow bringing Pacific moisture into the mountains, which is subsequently forced to lift up their slopes and deposit significant precipitation, primarily between August and May. Mesoscale convective systems are common mid-summer near the central border with the United States from the Prairie provinces eastward towards the Great Lakes. Southeastern sections of the country are also wet, due to the development of extratropical cyclones along the east coast of the continent which move northward into Atlantic Canada. During the summer and fall months, tropical cyclones from the Atlantic basin are also possible across Atlantic Canada. Amounts decrease as one works farther inland from the Pacific and Atlantic coasts, and from south to north towards the Arctic. Mexico Rainfall varies widely both by location and season. Arid or semiarid conditions are encountered in the Baja California Peninsula, the northwestern state of Sonora, the northern altiplano, and also significant portions of the southern Altiplano. Rainfall in these regions averages between per year, with lower amounts across Baja California Norte. Average rainfall totals are between in most of the major populated areas of the southern altiplano, including Mexico City and Guadalajara. Low-lying areas along the Gulf of Mexico receive in excess of of rainfall in an average year, with the wettest region being the southeastern state of Tabasco, which typically receives approximately of rainfall on an annual basis. Parts of the northern altiplano, highlands and high peaks in the Sierra Madre Occidental and the Sierra Madre Oriental occasionally receive significant snowfalls. Mexico has pronounced wet and dry seasons. Most of the country experiences a rainy season from June to mid-October and significantly less rain during the remainder of the year. February and July generally are the driest and wettest months, respectively. Mexico City, for example, receives an average of only of rain during February but more than in July. Coastal areas, especially those along the Gulf of Mexico, experience the largest amounts of rain in September. Tabasco typically records more than of rain during that month. A small coastal area of northwestern coastal Mexico around Tijuana has a Mediterranean climate with considerable coastal fog and a rainy season that occurs in winter. Tropical cyclones track near and along the western Mexican coastline primarily between the months of July and September. These storms enhance the monsoon circulation over northwest Mexico and the southwest United States. On an average basis, eastern Pacific tropical cyclones contribute about