Preliminary data indicates that the statewide average temperature in September was 69.0o F, which is 1.0o F above the 1981-2010 mean value of 68.0o F (Figure 1). September 2020 was the 35th warmest September since observations began in 1895.
Delaware’s statewide precipitation for September 2020 averaged 3.99 inches, 0.02 inches above the 1981-2010 mean (Figure 2), placing this month in the “normal” category for all months since 1895.
Statewide Spatial Anomalies
Data from the Delaware Environmental Observing System (DEOS) show that temperature departures were generally small, and varied in sign, throughout the entire state (Figure 3). Precipitation anomalies differed greatly depending upon location. Kent and northern Sussex counties showed large positive precipitation anomalies while northern New Castle County saw substantial negative anomalies (Figure 4).
Temperatures were above normal across most of the western one-third of the country (5 – 10o F), while below normal temperatures were found across the Great Plains. Most of the eastern United States saw near normal temperatures during the month (Figure 5). Precipitation was generally below normal across the majority of the United States, while above normal precipitation fell across the southeastern portions of the country (Figure 6). The 500 hPa height pattern for September exhibits a ridge dominating the western portion of North America leading to generally warm and dry weather across that region which continues to contribute to the severe wildfire season (Figure 7).