The climate of the district is predominantly hot and dry to the west of the watershed, hot and moist eastward of it; but very cold weather is apt to prevail for a few weeks in January and February, with strong north winds, on both sides of the watershed, and the transition from piercing cold to great heat at these times is often brought about very suddenly by a change of wind direction. There is seldom any frost, but water-bags are occasionally frozen on the mountain tops at night. Cool north-west winds prevail in the north part of the area, while hot damp winds from the south-east are usual in the south. In the central part, round Berenice, absolute calms are frequent.[39] The highest mountain-masses are frequently swathed in clouds for weeks together, especially from January to March. The hot, dry, sand-laden winds called _Khamsin_ occasionally blow for four or five days together in March and April; at these times the shade temperature rises to over 45° C., and the air is thick with sand and dust. Rain falls in most years, but its quantity is very variable; in some years there is barely enough to keep the wells supplied, and much of the vegetation withers; in others, heavy storms produce wild downrushes in the wadis, filling them for short periods with raging torrents. Curious electrical and optical phenomena can sometimes be seen on the mountain-tops during storms and in mists.[40] The Elba region is seldom free from clouds, and receives far more rain than any other portion of the area, forming in fact the northern limit of the rainy tropical zone; it is in consequence relatively well wooded, while the other mountains are a dreary waste of naked rocks. PLATE II. [Illustration: SKETCH-MAP OF SOUTH-EASTERN EGYPT. Showing Drainage-Basins. Ball. Geography & Geology of South-Eastern Egypt. Photo-Metal-Process. Survey Dept. Cairo 1910. (60-190) Scale 1:2,000,000.] =Scenery.=