current_season_summer

current_season_summer = {
	#southern region with rainy/dry seasons
	trigger_if = {
		limit = {
			location = {
				geographical_region = seasonal_region_deccan
			}
		}
		current_month >= 3
		current_month < 6
	}
	trigger_else_if = {
		limit = {
			location = {
				geographical_region = seasonal_region_rajasthan
			}
		}
		current_month >= 4
		current_month < 7
	}
	trigger_else_if = {
		limit = {
			location = {
				geographical_region = seasonal_region_bengal
			}
		}
		current_month >= 4
		current_month < 6
	}
	trigger_else = {
		#Generic Northern Hemisphere
		current_month >= 6
		current_month < 9
		#Not present/has different name in these regions
		location = {
			NOR = {
				geographical_region = seasonal_region_west_africa
				geographical_region = seasonal_region_east_africa
				geographical_region = seasonal_region_peninsular_southeast_asia
				geographical_region = seasonal_region_maritime_southeast_asia
			}
		}
	}
}

As written in game/common/scripted_triggers/00_weather_triggers.txt.