How Well Did La Nina Precipitation Climatology Perform in November?

Highlight: La Nina is choppy moderate strength. How dis November La Nina climatology verify for U.S., Australia and South America.

Fig. 1: The 12-week Nino SSTA observations reveal choppy moderate La Nina.

Discussion: The Nino SSTA regions reveal a choppy moderate-strength La Nina (Fig. 1). The November 2020 global La Nina climate is intact based on a -1.2 multivariate ENSO index (MEI). So how did La Nina precipitation climatology (from the past 25 years) for November compare with actual precipitation in the U.S., Australia and South America? In the U.S. the November 2020 precipitation pattern is dry in the Mid-south States (Fig. 2). The La Nina climatology is MUCH drier (Fig. 3). Typically, November La Nina is very wet in the Northwest whereas this year the heavy precipitation was shifted farther north. In Australia, the November 2020 rainfall pattern was dry across the north and east continent (Fig. 4) which is just the opposite of a typical La Nina November climate (Fig. 5). In South America the observed precipitation indicates patchy areas of anomalous wet or dryness (Fig. 6) compared to the bold wet Brazil and dry Paraguay/Uruguay climatology (Fig. 7). The lack of classic La Nina precipitation patterns observed in November is blamed in-part on the presence of unusual large areas of warmer-than-normal SSTA in the global subtropics and middle latitudes (Fig. 8).

Fig. 2-3: The November 2020 United States rainfall anomalies compared to moderate (or stronger) La Nina climatology from 1995-2020.

Fig. 4-5: The November 2020 Australia rainfall anomalies compared to moderate (or stronger) La Nina climatology from 1995-2020.

Fig. 6-7: The November 2020 South America rainfall anomalies compared to moderate (or stronger) La Nina climatology from 1995-2020.

Fig. 8: The lack of classic La Nina precipitation patterns in November is likely related to the effects on climate by widespread anomalous warm SSTA outside of the tropics.