Middle Latitude Ocean Temperature Anomalies Responsible for July 2018 Climate Extremes in Northern Hemisphere

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Discussion: Many areas of unusually hot temperatures coupled with drought conditions affected northern hemisphere locations during mid-summer 2018. The cause of the anomalous heat and dry climate is related in-part to warm sea surface temperature anomalies (SSTA) in the middle latitude northern hemisphere oceans (Fig. 1) and the tendency for 500 MB upper high pressure ridge areas (Fig. 2) causing the heat and dryness to form over or downwind the warm SSTA regions.  The evolution of the middle latitude high pressure zones causing climate extremes is somewhat independent of the El Nino southern oscillation (ENSO) yet having great influence on climate across major population areas and crop regions.

Fig. 1: Global sea surface temperature anomalies (SSTA) for July 2018 as calculated by the International Research Institute for Climate and Society.

Fig. 2: Global 500 MB anomalies for July 2018 as calculated by the International Research Institute for Climate and Society.

In July 2018 widespread historic anomalous heat affected Europe to Western Russia including the Black Sea region (Fig. 3). Record heat also affected to Southwest U.S. centered on California. Excessive heat affected China and the Northeast U.S. to Quebec. Dryness attached to the high pressure zones affected Europe, Central Russia, the Northwest U.S. and Eastern Corn Belt plus Mexico during July (Fig. 4). A stalled Madden Julian oscillation (MJO enhanced the Southeast Asia Monsoon and West Pacific tropical cyclone activity in July 2018.

Fig. 3: Global surface temperature anomalies for July 2018 as calculated by the International Research Institute for Climate and Society.

Fig. 4: Global precipitation anomalies (SSTA) for July 2018 as calculated by the International Research Institute for Climate and Society.