Elections Alberta has published the unofficial voter turnout for the advance polls.
There were 4 days of advance polling, from April 29 to May 2.
According to Elections Alberta there was a 31% increase in participation in advance polls between 2012 (179,820 voters over a three day period) and 235,410 voters in 2015.
There was a 12% increase in the voters list since 2012, which may account for some of the increase. But it seems like advanced polls are becoming more popular (see the recent increase in PEI) as voters take advantage of the convenience of multiple days of voting opportunities.
Polls close tonight at 8:00pm Mountain Time, and unofficial results and voter turnout should become available shortly after.