Average Temperature Outlook for CLE ELUM (issued in February 2015) suggests that during Mar-Apr-May 2015:

There is a 99% chance that the average 3-month temperature will be within the range of 42.2 and 50.4 Deg F,.

There is a greater ( 68.0%) chance that the temperature will be higher than the climatological median* of 46.3 Deg F, and a lesser (32.0%) 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.