A map from 1906 of North America showing the mean annual isotherms of the region given in degrees Fahrenheit. "The climate of North America naturally varies greatly, depending on latitude, the general atmospheric circulation or direction of the prevailing winds, and the form and relief of the land areas. The influence of latitude is evident as we proceed from the tropical climate of Central America to the arctic climate of the far north. The greater part of the continent lies within the region of the anti-trades or prevailing west winds, and as a consequence the Pacific coast has an insular climate, moist and without great extremes of temperature. As the mountains lie near the coast, the winds soon lose their moisture, and the interior region east of the coastal ranges has but a slight rainfall and is largely arid or desert, presenting the wide extremes of temperature and rather light rainfall which are characteristic of a continental climate. The rainfall gradually increases as we approach the Atlantic Ocean and Gulf of Mexico, the great sources of supply for the eastern region. The effect of the difference in climate brought about by the prevailing winds, tempered as they are by the surface over which they have blown, is seen in the difference between the climates of similar latitudes in Labrador and southern Alaska. Proceeding from the region of the anti-trades to that of the trade winds, the conditions are reversed, and it is now the east coast which receives the rainfall." - Hart, 1906, p. 17.