冻雨是一种特殊的降水现象，通常发生在冬季或早春。它并非一开始就是冰，而是以液态雨滴的形式从云中落下，但在下落过程中穿过近地面的一层低于0℃的冷空气，使得雨滴温度降至冰点以下却仍未结冰，形成所谓的“过冷水滴”。当这些过冷水滴接触到地面、树木、电线或其他低于0℃的物体表面时，会迅速冻结成一层透明而光滑的冰壳，这种现象就称为冻雨。冻雨的形成需要特定的大气温度结构：高空温度高于0℃，使水汽凝结为液态雨；中层有一层低于0℃的冷空气；而近地面又存在一个更冷的薄层（通常低于0℃）。这种“暖-冷-更冷”的垂直温度分布是冻雨形成的关键条件。与普通的雨夹雪或冰雹不同，冻雨造成的冰层非常光滑且附着力强，容易导致道路结冰、电线断裂、树木折断等灾害，对交通、电力和农业造成严重影响。因此，气象部门在预报冻雨时会特别关注低空温度剖面的变化，以便及时发布预警，减少其带来的危害。
Freezing rain is a unique type of precipitation that typically occurs during winter or early spring. It doesn’t start as ice; instead, it falls from clouds as liquid raindrops. However, as these drops descend through a shallow layer of sub-freezing air near the ground (below 0°C or 32°F), they become supercooled—meaning their temperature drops below freezing without turning into ice. When these supercooled droplets strike surfaces such as roads, trees, power lines, or any object at or below 0°C, they instantly freeze upon contact, forming a smooth, transparent glaze of ice.The formation of freezing rain requires a specific vertical temperature profile in the atmosphere: above-freezing temperatures aloft to produce liquid rain, a mid-level layer of sub-freezing air, and a very shallow cold layer right at the surface (also below freezing). This ‘warm-over-cold’ structure is essential for freezing rain to occur. Unlike sleet or hail, freezing rain creates a slick, hard-to-remove ice coating that can lead to hazardous road conditions, downed power lines, and damaged trees, posing significant risks to transportation, infrastructure, and agriculture.Therefore, meteorologists closely monitor low-level temperature profiles to accurately forecast freezing rain and issue timely warnings to mitigate its potentially severe impacts.
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