Preliminary data indicates that the statewide average temperature in December was 38.2° F, which is 1.3° F below the 1991-2020 mean value of 39.5° F (Figure 1). December 2022 was the coolest December Delaware has seen since 2017.
Delaware’s statewide precipitation for December 2022 averaged 4.48 inches, 0.63 inches above the 1991-2020 mean (Figure 2). This month’s precipitation was in the top one-third of values since observations began in 1895.
Statewide Spatial Anomalies
Data from the Delaware Environmental Observing System (DEOS) show that temperature departures were generally negative across the entire state (Figure 3) with some stations seeing negative anomalies of up to 2.0° F. Precipitation anomalies were uniformly positive across the entire state, with the largest positive anomalies found in Kent County (Figure 4).
Temperatures were below normal across most of the northern tier of the western United States, and along portions of the Atlantic Coast (Figure 5). Much of the southern tier of the United States, and New England saw above normal temperatures. Precipitation departures were mixed across the country, with the largest positive precipitation anomalies found in California, helping to relieve drought conditions there (Figure 6).
The 500 hPa height pattern for December shows a jet stream trough over the western United States contributing to the temperature anomalies across that region (Figure 7).