Mercer Island Washington Climate Data

Monthly Average Climate Data for Mercer Island Washington

Switch Data to Celsius/Metric Units
MonthAvg. LowAvg. HighAvg. Precip
January35.7 °F46.7 °F5.58 in.
February35.6 °F49.3 °F3.9 in.
March37.9 °F53.3 °F4.4 in.
April41.2 °F58.5 °F3.26 in.
May46.7 °F65.4 °F2.09 in.
June51.0 °F69.7 °F1.85 in.
July54.5 °F76.3 °F0.79 in.
August54.7 °F76.8 °F0.97 in.
September50.9 °F71.0 °F1.64 in.
October44.6 °F60.1 °F4.14 in.
November39.0 °F51.1 °F6.61 in.
December35.2 °F45.7 °F6.18 in.
Annual43.9 °F60.3 °F41.41 in.

Climate Data for Mercer Island Washington

Average First Frost DateNov. 11 - Nov. 20
Average Last Frost DateApr. 1 - Apr. 10
Average Days With Frost30-40 Days
Plant Hardiness Zone - 2023Zone 9a : 20°F to 25°F
Plant Hardiness Zone - 2012Zone 8b : 15°F to 20°F
Current Drought ConditionsAbnormally Dry
Köppen Climate ClassificationCsb - Warm-Summer Mediterranean Climate