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

There is a 99% chance that the average 3-month temperature will be within the range of 42.8 and 52.0 Deg F,.

There is a greater ( 76.0%) chance that the temperature will be higher than the climatological median* of 47.4 Deg F, and a lesser (24.0%) 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.