Distribution of precipitation during the year differs among regions within the Great Plains.
Most of Texas and Oklahoma have pronounced bimodal regimes with peak levels of rainfall occurring both during May-June and September-October.
In contrast, most of the rest of the Great Plains has a unimodal regime with peak precipitation occurring only during May or June.
Regardless of the regime, 70 to 75% of the annual precipitation occurs during the growing season.
Unimodal Precipitation Regime
Bimodal Precipitation Regime