Finally, and just in the nick of time, gentler weather has arrived so that March can go out in the prescribed manner **.
Crocuses in a corner, tulips in a row.
** In the evening at the beginning of March, Leo the Lion rises in the east just after dusk to bring March in.
After the vernal equinox, the Sun is in Aries the Ram (lamb), the first sign of the zodiac. Therefore, at the end of March "the lamb" is setting in the west at dusk, and taking March out with it.
So from an astronomical point of view, the saying more correctly would be, "March comes in with the lion, and out with the lamb." However in this case meteorology trumps astronomy and so we say, "March comes in like a lion, and out like a lamb."