Why does rainfall decrease from east to west in the prairies of north America?

Answer 1

Prairies are typically located.

1. To the west of these grass lands are the mountain ranges of Rockies. To the East is the river Mississippi. Then farther east are the Appalachian mountains.Thus the Westerly winds are not likely to be responsible for the bulk of precipitation in the Prairies. The winds coming up from the Gulf along the great river should be giving the precipitation. Summer features depending on local water sources like the Great lakes and the MM river system should add to the annual rain fall. The in blowing polar easterlies in winter from Canada will bring precipitation but once again it decreases from E to W, though not so significantly from N to S either as snow or rain or both.

2. As the moisture laden winds ascend the up slopes of the prairies the rain fall must naturally decrease from the East to the West.

3. The rain fall must decrease not only from East to West, but also from South to North,in USA and this factor must be the dividing line between red and white wheat areas when it is influenced by temperature.

4. The westerlies are arrested by the mountain walls on the Pacific coast. are they not? No sooner the Pacific coast mountains and Sierras are crossed we find deserts and mountainous climates even before reaching the Rockies.

5. It seems a correction is needed in the directions mentioned. In the northern hemisphere the westerlies, generated in the subtropical highs blow from southwest to northeast, rather than NW to SE as stated. But that is not the issue. The coast ranges of western cordilleras act as the first barrier and the wind ward side of Rockies act as the last barrier for the westerly influence to reach the prairies from the West. Thus either in Canada or in US the Westerly wind influence can at the most reach the western or wind ward side of the Rockies, so Prairies are deprived of that share of rain as those are on the lee ward side.

6. The Easterly ifluence that might have reached the prairies is stopped by the Appalachians though the Gulf stream adds to the increase of rains, on the US coasts. On the Canadian part the winds are off shore.

Source:Elements of Geography by Finch and Trewartha & others. see sections on BSk, Caf, and Daf types of climates.Other sources North America by JH Stembridge-OUP-Chapter III