ONSET OF THUNDERSTORMS AND PRECIPITATION OVER NORTHERN NIGERIA

An empirical prediction scheme for the start of thunderstorms, and the onset and expected amount of rainfall for any year at Kano, Nigeria, is presented, using 8 years' upper air data. The years investigated include two drought years (1973 and 1974) and 3 years of above average rainfall (1978, 1980 and 1988). Agriculturally sufficient and reliable rainfall begins 5-6 weeks after the vertical wind shear below the African Easterly Jet, DELTA-U(L) (surface, 700 hPa), and the mid-tropospheric shear DELTA-U(M) (700-400 hPa), simultaneously satisfy the condition -20 less-than-or-equal-to DELTA-U(L) less-than-or-equal-to -5 ms-1 and 0 less-than-or-equal-to DELTA-U(M) less-than-or-equal-to 10 ms-1, as previously put forward by Omotosho. The total precipitation for any year is found to be well correlated with the total moisture anomaly (specific humidity) from the week of the above-critical wind shear to the week of rainfall onset. This makes it possible to estimate the expected rainfall total at the very onset of the rains.