Okay, my email has been full of material on the humidity issue and paper ballots.

It turns out that Doug Jones of Iowa has written a bit about this problem relating to optical scanning devices:

t is worth noting that paper ballots change size slightly with changes in humidity! Commercial printers use the rule of thumb that a 10% increase in relative humidity causes paper to expand by about by one part in 1000; as a result, the size of a piece of bone-dry paper could expand by as much as 1% as it picks up moisture in an extremely humid environment. This comes to 1/10 inch in 10 inches, while many mark-sense voting targets are about 1/8 inch in their short dimension!

The early mark-sense scanners used for scoring tests solved the problems caused by humidity changes by storing all test papers in a controlled atmosphere for some time prior to tabulation, but on modern mark-sense vote tabulators, the design accommodates humidity changes by spacing the sensors to the midrange of variation in paper size and using voting targets that are wider than the sensors.
…

If one or more of the top or bottom index marks are not seen on a pass through the scanner, the scanner typically stops with an error message indicating a misfeed. This could be due to an extreme dimensional change in a ballot, for example, because the humidity is too high for reliable scanning or because the paper has been crumpled and then flattened, or it could be because the paper passed through the scanner on a diagonal.

The fact that sensing tracks are narrower than the voting target means that a mark may be seen on one pass through the scanner and not on a later pass, perhaps because of a humidity change from one pass to the next. The fact that a ballot may be on a slight diagonal as it is scanned introduces the possibility that identical marks in two different places on the ballot might be counted differently, even when they are seen by the exact same photosensor.

And here is a report from 2004 in Lawrence, Kansas:

Today’s humidity did more than make voters uncomfortable — it also helped gum up the works during vote counting at the county courthouse, election officials said.

Marni Penrod, deputy Douglas County Clerk, said Tuesday night that one of the county’s two vote counting machines typically was susceptible to minor problems related to the counting of paper ballots. But today, in particular, the high humidity made some ballots stick together and the machine had trouble counting some ballots.

Ballots from two precincts were particularly troublesome: Those from the North Wakarusa precinct, which votes at Wakarusa North Fire Station and those from the Coffin Sports complex at Haskell Indian Nations University. Neither of those polling stations have air conditioning.

“There were a lot of problems with those ballots, Penrod said. “They’ve gathered a lot of humidity all day.”

And there were many other similar reports …

Thanks to those of you who mailed me these materials and examples today.