Emergencies and elections don't get along well. The threat of emergencies, like acts of terrorism or massive weather events, remain a concern in elections, but we seem to lack many structures in place to handle such events.
Fires in Sonoma County, California prompted Governor Jerry Brown on October 19, 2017 to sign an executive order declaring an all mail ballot election for the November 7 election.
I was a bit skeptical of what I thought to be a fairly late emergency declaration and wondered how it might play out. Granted, it's an admittedly low-turnout election, but on the surface it appears that canceling in-person voting had a negligible impact, if any, on turnout.
The 2013 election had 6364 absentee and 1248 precinct ballots for 35.2% turnout. The 2015 election had 7003 absentee and 1235 precinct ballots for 33.0% turnout. Surely, a high percentage of voters already casting absentee ballots helps minimize any damage from canceling precinct voting. The final results this election were 6590 absentee for 31.2% turnout--a decline, but no bigger than the previous off-year-over-year decline.
I'm certainly not equipped to address matters like the competitiveness of the candidates or contentiousness of the issues or any of the many other confounding variables that could affect turnout. But, it's a small data point to consider in the larger scheme of thinking about how to handle emergencies and elections.