Ranking the U.S. January 2020 Climate: 6th warmest on record.
January 2020 discussion: After the 6th warmest December on record the month of January was just-as-warm ranking 5th warmest in the 1895-2020 climatology. There were no state records but 18 states ranked MUCH ABOVE normal (Fig. 1) in the top 10% warmest all-time. Regionally, the Northeast U.S. ranked warmest. All of the lower 48 contiguous U.S. ranked above normal for mid-winter.
Fig. 1: The statewide average temperature rank analysis by NOAA for January 2020.
January 2020 ranked 25th wettest all-time. The stormiest locations were Oklahoma to Illinois plus Mississippi and also Washington (Fig. 2). The majority of the precipitation was heavy rain. California to the Great Basin and Arizona were drier than normal and Massachusetts/Rhode Island were very dry (and lacking snowfall) for mid-winter.
Fig. 2: The statewide average precipitation rank analysis by NOAA for January 2020.
Explanation: There is a tendency to attribute unusually warm climate regimes/events to climate change or global warming. While this assessment is likely partially true a more vigorous investigation is required especially for market interests. In January 2020 two very specific climate diagnostics were in-place leading to the very warm early 2020 climate: 1.) Strong arctic oscillation (+AO) and 2.) Widespread regional warm SSTA. The AO was +2.415 in January which is 3rd strongest on record. This means the polar vortex was at a far north location and encouraged mild westerly flow across a very warm ocean surface causing the mid-latitude warmth in the northern hemisphere mid-winter. What caused the strong +AO is not known. Speculated is the possible lag effect of a long-duration inactive sun and the atmospheric response by the earth during northern hemisphere winter. The +AO combined with a tendency (since 2013) for large regions of warm ocean temperatures separate from the ENSO regime to enhance the warm climate.
Fig. 3: The upper air pattern for January 2020 identifies an intense polar vortex near the North Pole which encourages mild temperatures in the middle latitudes.
Fig. 4: Much of the global ocean surface was warmer than normal during January 2020 independent of ENSO usually considered the primary climate-driver. Reginal SSTA patterns are now the leading influence of oceans on global climate.