The Wettest 12 Months Ever for Cincinnati

This post departs from my regular routine and does not coincide with my Inside The Forecast segment for the day.

We all know that Cincinnati had the wettest year ever in 2011 recording 73.28" of rain. Included in the total of course is melted snow and ice.

But if you think about it a year is an artificial division of time relative to weather. In fact so are weeks months and 24 hour days.  It is not a difficult concept weather events are not confined to time intervals humans define.

But .... we have to organize the information some way so we talk about wettest days, months and years.

The reality is that by looking at rain totals over intervals of 12 consecutive months we can gain better insight.

That is just what I did.  Reliable monthly rainfall data goes back to November 1834 and official monthly data back to November 1870.  The earlier data set was observed by teachers at Woodward College (later High School) in Over The Rhine, Downtown Cincinnati.  The official data was less than half-mile away also in  Downtown Cincinnati.  The Woodward data later moved to near the entrance of Eden Park about one mile into Walnut Hills from Downtown.

The data sets overlap from November 1870 through December 1902. I mention this because it allows us to compare the two and judge the accuracy of the unofficial data. The two are comparable.

For 12-consecutive month periods the wettest is 77.09" from Feb 2011 through the end of Jan 2012 almost 4" greater than the wettest year in history at 73.28".

The Table below lists the 20 wettest 12 month periods in Cincinnati history. The columns are year, ending month, total rainfall and departure from the normal annual rainfall for the 1981-2010 normal period.

20 Wettest 12-Month Periods

2012	1	77.09	34.57
2011	12	73.28	30.76
2011	11	68.53	26.01
2011	10	67.14	24.62
1847	10	66.59	24.07
1847	11	66.28	23.76
1880	6	65.46	22.94
1847	12	65.18	22.66
1880	7	65.17	22.65
1848	3	65.15	22.63
1848	1	65.05	22.53
2011	9	64.60	22.08
1848	5	64.41	21.89
1848	2	63.80	21.28
1848	4	63.58	21.06
1882	9	62.31	19.79
1882	8	61.25	18.73
1880	5	60.82	18.30
1847	7	60.74	18.22
1882	5	59.95	17.43

By the way the driest 12-month period in Cincinnati history enede November 1901 with only 15.63" of rain while the driest year in Cincinnati was 1901 with 17.99" of rain.

So you see consecutive 12-month periods tell a more extreme story than calendar year data.

Here are the 20 driest 12-month periods in Cincinnati history. The columns are the same as for wet periods.

20 Driest 12-Month Periods

1901	11	15.63	-26.89
1902	3	17.71	-24.81
1901	12	17.99	-24.53
1902	2	18.25	-24.27
1902	4	18.65	-23.87
1902	1	19.22	-23.30
1901	10	19.39	-23.13
1901	8	19.61	-22.91
1931	2	20.14	-22.38
1931	3	20.20	-22.32
1901	9	20.25	-22.27
1857	3	21.13	-21.39
1941	5	21.20	-21.32
1931	1	21.21	-21.31
1857	2	21.88	-20.64
1905	3	22.07	-20.45
1931	4	22.08	-20.44
1871	6	22.33	-20.19
1857	1	22.39	-20.13
1902	5	22.57	-19.95