Weather clutter was measured using an L-band long-range (200 nmi.) air-route surveillance radar (ARSR), from the stored data of five scans. It is shown that weather clutter obeys a Weibull distribution, and moreover such Weibull-distributed weather clutter also obeys a Weibull distribution after passing through a moving target indicator (MTI) processor realized by a double canceller. Some adaptive methods for suppressing Weibull-distributed clutter are summarized.