An early-season heavy snowfall struck central & northern Indiana on October 25, 1805.
At the White River Mission, a fort on the White River in Madison County, a diary mentioned that “it began to snow hard” on the afternoon of the 25th. It also stated “the Indians were frightened on account of it. They said they had never seen the like, this time of year, in this place….”
By the morning of the 26th, the entry read, “it looks as it does in mid-winter.” Fort Wayne reported 12” of snowfall.
Northern Ohio reported up to 3" snowfall.
Lack of settlement where the heaviest snowfall occurred made snowfall reports from this system scant.
Snow may not have fallen at Vincennes, Indiana (southwest part of the state), as there is no mention of it in local press there. That was one of the few main early settler settlements in the state in 1805.
In Lewis & Clark's Expedition, Clark states in his diary from the Columbia Gorge area of Washington & Oregon:
The morning fare after a beautifull night, the nativs approached us this morning with great caution. our two old chiefs expressed a desire to return to their band from this place, Saying "that they Could be of no further Service to us, as their nation extended no further down the river than those falls, [NB: they could no longer understand the language of those below the falls, till then not much difference in the vocaby.]  and as the nation below had expressed hostile intentions against us, would Certainly kill them; perticularly as They had been at war with each other;" we requested them to Stay with us two nights longer, and we would See the nation below and make a peace between them, they replied they "were anxious to return and See our horses" we insisted on their Staying with us two nights longer to which they agreed; our views were to detain those Chiefs with us untill we Should pass the next falls, which we were told was verry bad, and at no great distance below, that they might inform us of any designs of the nativs, and if possible to bring about a peace between them and the tribes below.
There are many mentions of how nice, bright, sunny & warm the weather was. Typically, it turns quite wetter during this time, but the drier, pleasant weather indicates upper ridging in the West, which promotes troughiness & cold weather in the East. This makes sense as the historic snowstorm pivoting up through the Ohio Valley & Great Lakes.