The urban heat island effect, causes increased in the precipitation of upwind in the city. The warmer temperatures in cities, creates unstable air which leads to rain. Air is unstable when it is warmer than the air around it. The warm, unstable air starts to rise. The air cools as it rises, which allows water vapor within it to condense and form clouds. If the warm, rising air was carrying enough water vapor, those clouds can grow into rainclouds.
