Abstract
The thundery conditions which often develop in Egypt, Palestine and Syria, during the autumn, have been further investigated. They have been found to occur when the Sudan monsoon low intensifies towards the north and supplies the eastern Mediterranean with a warm southโeasterly current.
In a great many cases, shallow depressions form over the southeastern Mediterranean, or the adjacent land areas, as a result of the meeting of the above current with the relatively cold northeasterly air of antiโcyclonic distribution in Asia Minor. In a few cases they form over the western Desert in a manner resembling the formation of khamsin depressions. After being fully developed, these depressions move eastwards or northโeastwards, while the inflow of the cold air in the rear gives thundery showers. Such thunderstorms are specially marked over the sea, Palestine and Syria.
Over Egypt, however, highโlevel instability frequently exists between the warm current and the cool air advancing above. Owing to the stability of the surface layers, this highโlevel instability cannot pass into the thunderstorm stage without sufficient convergence of damp air. With a high degree of latent instability severe thunderstorms are then produced.