Abstract
In Kawantõ district when sõutherly wind blows, the overcasted weather and even sometimes drizzle is often experienced after the sunset, especially in morning, thought it is fine in day time. Some examples of such weather situation were investigated by synoptic atlas and it is found that they are explained by discontinuity between land and sea caused by nocturnal cooling of the land. The mode of the development of the discontinuity was mathematically treated under a simple assumption and the result was obtained which agrees well with the observation
