December 2021 – Near Record Warmth and Extremely Dry Conditions Across Delaware

December Temperatures

Preliminary data indicates that the statewide average temperature in December was 44.6o F, which is 5.1o F above the 1991-2020 mean value of 39.5o F (Figure 1).  December’s average temperature was the second highest since observations began in 1895

December Precipitation

Delaware’s statewide precipitation for December 2021 averaged 1.03 inches, 2.82 inches below the 1991-2020 mean (Figure 2).  This placed this month’s precipitation as the 5th lowest December precipitation since records began in 1895.

Statewide Spatial Anomalies

Data from the Delaware Environmental Observing System (DEOS) show that temperature departures were uniformly above normal across the entire State, with many stations seeing positive temperature anomalies of between 6o F and 7o F (Figure 3).  Precipitation was below normal across the entire state with some stations reaching negative anomalies of greater than 3 inches (Figure 4).

National Anomalies

Temperatures were above normal across most of the United States, with the largest positive temperature anomalies found across Texas and the lower Mississippi Valley.  Large areas of the country saw positive anomalies of 10o F to 13oF   Only the Pacific Coast and portions of Montana and North Dakota saw below normal temperatures for the month (Figure 5).  Precipitation anomalies varied greatly across the country (Figure 6), with excessively dry conditions across the High Plains of Texas, Oklahoma, and Kansas.  The 500 hPa height pattern for December shows a strong jet stream ridge located over eastern North America and a strong jet stream trough over northwestern North America contributing to the temperature extremes across those regions (Figure 7).


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