Об­ра­зуй­те от слова USUAL од­но­ко­рен­ное слово так, чтобы оно грам­ма­ти­че­ски и лек­си­че­ски со­от­вет­ство­ва­ло со­дер­жа­нию тек­ста.

People have been trying to predict the weather for thousands of years. In ancient times, they closely observed and remembered changes in clouds, wind and temperature that occurred just before _________________ weather events like hailstorms or floods.