Baddour, Omar (Direction de la Meteorologie Nationale, Casablanca, Maroc)
Morocco's climate is controlled by two major general circulation features that are depicted at sea level pressure by the Acores high and Saharian low. The first controls, according to its strenght and position, the alternance of nice and ramy weather during winter over a large part of Morocco. During summer and nearby periods, the Saharian low controls the easterly flow blowing from arid and hot region of the north African desert. Sometimes during this period of the year a vertical instability of the atmosphere take place in association with the presence of hot air at low levels and potentialy cold westerly air aloft.
The Atlas mountains barrier plays a great mesoscale influence on triggering and strengthening the convection and the associated storms. From climatological point of view, middle Atlas area corresponds to a maximum thunderstorm and hail days occurrence over the country. A yearly crop damage average in this area rises up to 200 Millions Dirhams (18 Millions USD) as reported by the Agricultural authority. Other damages such as humain and animal life loses is recorded nearly each year as a result of severe storm causing, in addition to hail fall, thunder strikes and flash floods. This paper gives some light on the thunderstorm and hail occurrence over the middle Atlas mountains. The investigation concerns the climatological averages, extremes and spatial temporal variability of thnderstorms and hail occurrence using 20 years data records from 1970 to 1990.