The Rain-shadow Effect Sheltered by mountains by Philip Eden
"Rain shadow" is a phrase often used by meteorologists in their
day-to-day work, and is occasionally mentioned by television
weather forecasters. Some may regard it as a solecism, but it
well describes the phenomenon whereby much less rain falls on
the lee side of a mountain range compared with the windward
side. Last week produced one of the best examples of the rain-
shadow effect we have seen in the UK in recent years thanks to a
persistent southwesterly airflow. Things are very different on
the leeward side of the mountains. The air-mass has now lost
much of its moisture, and as the winds descend the lee slope the
air becomes denser again, and therefore warmer. As it warms up
its capacity to hold moisture increases again, thus it is no
longer saturated. The mechanism which produced the persistent
rain on the windward slope is now switched off, the rain stops,
and the clouds dissipate. Last week's rain shadow effect (see
plot above) was very promi