At Greater Lafayette, 98 of 162 (1864-2026) Octobers have had at least a trace of snowfall during the month (60.4% of the Octobers since 1864 have had at least a few flakes).
However, the occurrence of October flakes or snowfall tends to cluster on the time line.
Note how the occurrence of getting snow flakes in October has been decreasing overall since the 1860s as the line slopes downward:
However, only 5 years have had flakes before October 12 & only 8 of those 162 Octobers have had MEASURABLE snow (0.1” or more) reported. So less than 5% have seen measurable, accumulating snowfall.
I have a post on the September 1942 snow flakes here & the accumulations in our northern counties (up to 4” at Wheatfield!). That is the only September I have ever seen records of snowfall in our forecast area back to 1895 so far & the only September at Greater Lafayette since 1864.
The second earliest snowflakes since 1864 were in 1987 when flakes fell on the morning of October 3.
That entire October was unusually cool, cloudy & wet while the western U.S. was unusually warm to hot & sunny.
Note the chunk of time at the Purdue Airport that was mostly cloudy to cloudy during the month (gray & light gray):