Preliminary data indicates that summer 2017 ranked as the 15th warmest summer season since records began in 1895 (tied with the 1995 and 2008 summer seasons). The statewide mean summer temperature of 75.3°F was 0.8°F above the 1981-2010 mean value of 74.5°F (Figure 1).
The statewide mean precipitation of 18.24 inches was 6.24 inches above the 1981-2010 normal of 12.0 inches, and was the 12th wettest summer season since 1895, and the 5th year in a row with above normal summer precipitation (Figure 2).
Statewide Spatial Averages
Data from the Delaware Environmental Observing System (DEOS) show that summer temperature anomalies varied between positive and negative, depending upon location within Delaware and Chester County, PA (Figure 3). The Wilmington/New Castle County Airport recorded 16 days of temperatures greater than or equal to 90°F, very near the 1948 – 2017 normal of 17 days.
Summer precipitation was above normal across the entire State (Figure 4). However, the size of the positive anomalies varied greatly from one location to another. The variable pattern of precipitation is due to the small-scale nature of convective storms; dropping heavy precipitation in some areas, while leaving others relatively dry.