Small Multiples

Accumulated precipitation by calendar year, Seattle.

An example of small multiple charting is shown above.  There are 16 small charts grouped together showing sixteen consecutive years of accumulated precipitation in Seattle Washington.  These small charts allow you to see if any patterns exist and, if so, also to see if certain years stand out compared to others.

The details of each chart is pretty low resolution.  But an overall pattern across all years is clear.  Seattle, in a calendar year view, is dominated by three clear periods: a wet first third (winterspring); a dry middle period (late spring-to-early fall); and a very wet late fall.  In fact, the season change is very predictable.  

Out in the west, the more common view is more often a water year view, with the water year beginning on October 1 and ending on September 30 of the following year.  A graph charted to that period would show a steady increase in accumulated precipitation followed by a long flat period, representing the droughty summers we typically experience from late May to October.  The chart on the bottom of the page illustrates this view.  Clearly, 2015-16 has been a wet period by any measure.

A close-up of a single year from the small multiple chart shown above.

A view of most of the same years shown above using a water year calendar (Oct 1 to Sep 30).