Jamieson, Fausset and Brown on Deuteronomy 11:14

14. the first rain and the latter rain--The early rain commenced in autumn, that is, chiefly during the months of September and October, while the latter rain fell in the spring of the year, that is, during the months of March and April. It is true that occasional showers fell all the winter; but, at the autumnal and vernal seasons, they were more frequent, copious, and important; for the early rain was necessary, after a hot and protracted summer, to prepare the soil for receiving the seed; and the latter rain, which shortly preceded the harvest, was of the greatest use in invigorating the languishing powers of vegetation (Jr 5:24; Joe 2:23; Am 4:7; Jas 5:7).