rain shadow

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun An area having relatively little precipitation due to the effect of a barrier, such as a mountain range, that causes the prevailing winds to lose their moisture before reaching it.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun meteorology an area of diminished precipitation on the lee side of mountains

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun an area that has little precipitation because some barrier causes the winds to lose their moisture before reaching it