The saying "in like a lamb, out like a lion" refers to the weather in the month of March. It suggests that March may start off mild and calm (like a lamb) but end with more fierce and stormy weather (like a lion).

"March comes in like a lion and goes out like a lamb."

It's a very old saying and refers to the weather in March----it means that March starts out with ferocious weather (e.g. mean, tough, and rainy), and then has gentle weather (warmer and mild).

The month of March.

March comes in harmful and goes out peaceful
It means it starts out with bad weather and end with good weather.

March is wet and windy at the begging and is warm and calm when it ends