Predicting the onset, severity, and duration of drought remains a challenge due to the number of interconnected variables that contribute to drought evolution and recovery (e.g., soil moisture, soil type, vegetation, land-use, topography, antecedent vegetative state/stress levels, and atmospheric circulation).  The interactions among these variables span spatial and temporal scales, increasing the complexity of drought prediction.

During the just-ending northern hemisphere winter the ocean surface east of New England has rocketed to 11-13F warmer than normal in some locations. The warming - very persistent in this location the past 7-8 years - is part of a weakening Atlantic Meridional Ocean Current which is slowing the transport of warm Gulf Stream Water toward Europe. Instead waters are warming (and rising) off the Northeast U.S. Coast. Blocking the warm water transport of the Gulf Stream is the North Atlantic Warm Hole south-southeast of Greenland. Climate Impact Company Research Scientist Olivia Kellner reviews the AMOC and NAWH.

Meteorological winter 2020-21 (so far) is very warm across the U.S. despite presence of a moderate-to-strong negative arctic oscillation also projected to last through February. During 3 analog years when -AO was similarly intense the Central/East U.S. experienced historic cold. The explanation for the warmer winter across the U.S. is related in-part to a constricted polar ice cap and warmer mid-latitude ocean surface.

La Nina 2020-21 has entered the mature phase. All dynamic forecast models indicate La Nina will begin to weaken during quarter 1 of 2021 shifting to neutral phase during quarter 2 of 2021. Specific climate influences are likely due to this transition on the U.S., South America and Australia.