The Pacific ranges, standing transverse to the course of the prevailing westerlies near the Pacific Ocean, are of the greatest importance in this respect; it is largely by reason of the barrier that they form that the tempering effects of the Pacific winds are felt for so short a distance inland in winter, and that the heat centre is displaced in summer so far towards the western coast.
The ranges of the Rocky Mountains in their turn receive some rainfall from the passing winds, but it is only after the westerlies are reinforced by a moist indraft from the Gulf of Mexico and the Atlanticthe result of summer or of cyclonic inflowthat rainfall increases to a sufficient measure on the lower lands to support agriculture without irrigation.
In California the effect of the strong equatorward turn of the summer winds is to produce a dry season; but in the states along the Gulf of Mexico and especially in Florida the withdrawal of the stormy westerlies in favor of the steadier trade winds (here turned somewhat toward the continental interior, as explained below) results in an increase of precipitation.
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