# January averages
t.rast.series input=monthly_aggregates \
    output=jan_average method=average \
    where="start_time = datetime(start_time, 'start of year', '0 month')"

# February averages
t.rast.series input=monthly_aggregates \
    output=feb_average method=average \
    where="start_time = datetime(start_time, 'start of year', '1 month')"

# March averages
t.rast.series input=monthly_aggregates \
    output=mar_average method=average \
    where="start_time = datetime(start_time, 'start of year', '2 month')"