Albert Barnes Commentary Deuteronomy 11:14

"that I will give the rain of your land in its season, the former rain and the latter rain, that thou mayest gather in thy grain, and thy new wine, and thine oil." — Deuteronomy 11:14 (ASV)

The first rain and the latter rain - The former is the proper term for the autumn rain, which falls around the time of sowing, and is known as “the former” because it occurs in the early part of the Hebrew civil year, namely, in October and November. The other word refers to the spring rain, which falls in March and April, because it prepares the earth for the ingathering of the harvest. Between these two wet periods, and apart from them, there was little or no rain in Canaan.