rain用a few或者a little都是可以的。都表示小雨的意思。
举例：
About five o'clock next morning there were a few drops of rain in the wind.
清晨五时许疏疏落落下了几点雨。有风。
In the desert, as we know, there is a little rain but it is not good enough for most plants.
正如我们所知，沙漠还是会下雨的，但对大多数植物来说这点雨量并不足够。