Most / Least Educated Cities in WA. The average temperature of Ellensburg is 48.68°F, which is lower than the Washington average temperature of 50.47°F and is much lower than the national average temperature of 54.45°F.5.03 mph. U.S. 16.93 mph. * The temperature, snow fall, and precipitation information on this page were calculated from the historical data of 18,000+ U.S weather stations for the period of time from 1980 to 2010.