Читать книгу Weather For Dummies - John D. Cox - Страница 49

When a warm front moves into the space occupied by a retreating cold air mass, it develops a completely different precipitation pattern than an advancing cold front would. While a cold front digs in underneath a warm air mass, because its air is denser, the lighter air of a warm front rides up above the cold air it is replacing. In this rising warm air, clouds form far out ahead of the advancing warm front’s boundary. Hundreds of miles ahead of the surface edge of a warm front, the cloud cover slowly thickens, finally bringing rain or snow. All this happens long before the surface edge of the warm front finally passes. When that happens, the sky is usually clear. A typical warm front can travel about 10 to 20 miles per hour, most often moving north and east.