Average Temperature Outlook for CLE ELUM (issued in July 2015) suggests that during Aug-Sep-Oct 2015:

There is a 99% chance that the average 3-month temperature will be within the range of 53.6 and 60.8 Deg F,.

There is a greater ( 77.0%) chance that the temperature will be higher than the climatological median* of 57.2 Deg F, and a lesser (23.0%) chance that the temperature will be lower than the climatological median*.

*For the climatological reference information, the median statistic is reported. The median value means that during the present climatological reference period (1981-2010), half of the years (50%) temperature was greater than the median and in the other half (50%) less than that.