In meteorology, March is said to come in like a lion and go out like a lamb. This is because spring is slowly arriving. The North Pole tilts more toward the Sun as Earth orbits in its yearly procession. In the Northern Hemisphere, more daylight hours and more direct rays of sunshine spell a warming on Earth. So while your lawn may be snow covered on March 1 and the weather may be fierce, by March 31 there is a better chance for grass appearing and the gentle warming rays to be ushering in sweet weather.
In astronomy, March begins with the constellation of Leo the Lion rising in the east as the sun sets in the west. As Leo rises, it leads up a vast stretch of galaxies behind it. For astronomical observers, spring is known as galaxy season.
While there is no real "lamb" constellation, there is Aries the Ram, which is as close as we can come to March leaving like a lamb. Aries is ahead of Leo in the sky. Therefore, by the end of March, as the sun sets in the west, Aries the Ram sets just a bit behind it.