A box is plotted for each month of the year that has data.
The extents of the black box mark the lower quartile (25% of data values
are less than this value) and upper quartile (75% of data values
are less than this value), a red line indicates the median, and a
dark green line indicates the mean. The black lines above and below
the box, the "whiskers",
show the extent of the remaining data but have a maximum
length of 1.5L, where L is the length in meters from the lower quartile
to the upper quartile. Data values that extend beyond the whiskers
are "outliers" and are indicated with red crosses.
