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According to NOAA the meteorological summer (JUN/JUL/AUG) season of 2021 was the hottest on record given the 127-year climatology. Most of the West U.S. including California set all-time records for hottest summer on record. Nationally, the summer 2021 season was also wet ranking 8th wettest on record. Mississippi observed their wettest summer on record.

Highlight: U.S. Temperature and Precipitation Ranks for August and Meteorological Summer (JUN/JUL/AUG). Summer was hottest on record!

Discussion: The U.S. temperature rankings for 1895-2021 indicate summer 2021 was the warmest on record given the 127-year climatology. The record heat included state records for much of the West U.S. (Fig. 1). Twenty-five states ranked in the “much above average” category. Summer 2021 ranked 8th wettest on record. Mississippi observed their wettest summer on record while 13 other states received much above average” rainfall (Fig. 2). The North-central U.S. ranked 12th driest on record (where drought developed earlier this year).

In August, U.S. temperature rank was 4th hottest on record. California remained vigorously warm during summer ranking 6th hottest on record (Fig. 3). After a hot start to summertime in the Northwest, the strongest anomalous heat shifted to the East for mid-to-late summer. Most of the East ranked “much above average” during August while Vermont and New Hampshire set records. August was also a wet month ranking 14th wettest on record. There were no state records in August although 7 states from Utah to Alabama to New York ranked “much above average” for late summer (Fig. 4).

The global SSTA analysis (Fig. 5) for JUN/JUL/AUG 2021 reveals the climate correlation culprit leading to the anomalous warm and wet U.S. climate: Warmer-than-normal middle/high latitude sea surface temperature anomalies (SSTA). In the tropics ENSO was neutral and not a major factor on summertime climate in the U.S. The warm SSTA pattern across the middle/northern latitudes of the northern hemisphere reveal the influence on the upper air pattern (Fig. 6). Note that high-pressure ridging was dominant across and downwind the warm SSTA regions causing widespread anomalous warmth during summer 2021 for much of the high population regions of the middle latitudes in the northern hemisphere.

Fig. 1: NOAA state rankings and annotated national rank of temperature given the 1895-2021 (127 years) climatology for meteorological summer 2021.

Fig. 2: NOAA state rankings and annotated national rank of precipitation given the 1895-2021 (127 years) climatology for meteorological summer 2021.

Fig. 3: NOAA state rankings and annotated national rank of temperature given the 1895-2021 (127 years) climatology for August 2021.

Fig. 4: NOAA state rankings and annotated national rank of precipitation given the 1895-2021 (127 years) climatology for August 2021.

Fig. 5: Global SSTA regime for JUN/JUL/AUG 2021.

Fig. 6: The northern hemisphere upper air pattern for JUN/JUL/AUG 2021.