Extreme winter weather and a changing climate

The United States was virtually snow-free during the Christmas season 2023 matching a year which was one of the hottest globally since weather records have been kept. Yet, by early to mid January 2024, large sections of the United States were facing snow storms, blizzards, and extreme cold temperatures.

How does that sudden change of weather–from warmer than usual to extreme cold and snow–fit the arc of a changing climate now and into the future?

Featured articles:

*Francis, J. A., Skific, N., Vavrus, S. J., & Cohen, J. (2022). Measuring “Weather Whiplash” Events in North America: A New Large‐Scale Regime Approach. Journal of Geophysical Research. Atmospheres, 127(17), e2022JD036717. [PDF] [Cited by]

When weather conditions shift abruptly after a long period of the same pattern—for example, from a spell of abnormally mild temperatures to extreme cold, or from a long dry period to a parade of storms—major disruptions to ecosystems and human activities often ensue. These types of shifts have recently been dubbed “weather whiplash” events. In this study, we propose and demonstrate a new approach to measuring the frequency of these events based on continent-wide atmospheric regimes and their transitions. While the frequency of these events in recent decades has not changed substantially, our analysis of future model projections indicates robust increases and decreases in certain atmospheric patterns, particularly in those featuring an extremely warm or cold Arctic.

… In this study, we propose and demonstrate a novel metric to identify weather whiplash events (WWEs) and track their frequency over time. We define a WWE as a transition from one persistent continental-scale circulation regime to another distinctly different pattern, as determined using an objective pattern clustering analysis called self-organizing maps. We focus on the domain spanning North America and the eastern N. Pacific Ocean. A matrix of representative atmospheric patterns in 500-hPa geopotential height anomalies is created from 72 years of daily fields. We analyze the occurrence of WWEs originating with long-duration events (LDEs) (defined as lasting four or more days) in each pattern, as well as the associated extremes in temperature and precipitation. A WWE is detected when the pattern 2 days following a LDE is substantially different, measured using internal matrix distances and thresholds. Changes in WWE frequency are assessed objectively based on reanalysis and historical climate model simulations, and for the future using climate model projections. Temporal changes in the future under representative concentration pathway 8.5 forcing are more robust than those in recent decades. We find consistent increases in WWEs originating in patterns with an anomalously warm Arctic and decreases in cold-Arctic patterns.”

*Cohen, J., Agel, L., Barlow, M., Garfinkel, C. I., & White, I. (2021). Linking Arctic variability and change with extreme winter weather in the United States. Science, 373(6559), 1116-1121. [Cited by]

Despite the rapid warming that is the cardinal signature of global climate change, especially in the Arctic, where temperatures are rising much more than elsewhere in the world, the United States and other regions of the Northern Hemisphere have experienced a conspicuous and increasingly frequent number of episodes of extremely cold winter weather over the past four decades. Cohen et al. combined observations and models to demonstrate that Arctic change is likely an important cause of a chain of processes involving what they call a stratospheric polar vortex disruption, which ultimately results in periods of extreme cold in northern midlatitudes.”

The Arctic is warming at a rate twice the global average and severe winter weather is reported to be increasing across many heavily populated mid-latitude regions, but there is no agreement on whether a physical link exists between the two phenomena. We use observational analysis to show that a lesser-known stratospheric polar vortex (SPV) disruption that involves wave reflection and stretching of the SPV is linked with extreme cold across parts of Asia and North America, including the recent February 2021 Texas cold wave, and has been increasing over the satellite era. We then use numerical modeling experiments forced with trends in autumn snow cover and Arctic sea ice to establish a physical link between Arctic change and SPV stretching and related surface impacts.”

*Mi-Kyung, S., Seok-Woo, S., Yoo, C., Hwang, J., & Soon-Il An. (2021). Seesawing of Winter Temperature Extremes between East Asia and North America. Journal of Climate, 34(11), 4423-4434. [PDF] [Cited by]

In recent winters, there have been repeated observations of extreme warm and cold spells in the midlatitude countries. This has evoked questions regarding how winter temperature extremes are induced. In this study, we demonstrate that abnormally warm winter weather in East Asia can drive the onset of extremely cold weather in North America approximately one week forward. These seesawing extremes across the basin are mediated by the North Pacific Oscillation (NPO), one of the recurrent atmospheric patterns over the North Pacific. Budget analysis of the quasigeostrophic geopotential tendency equation shows that intense thermal advection over East Asia is able to trigger the growth of the NPO. Vorticity fluxes associated with the upper-level stationary trough then strengthen and maintain the NPO against thermal damping following the onset of the NPO. Differential diabatic heating accompanied by changes in circulation also positively contribute to the growth and maintenance of the NPO. These results imply that recurrent cold extremes, seemingly contrary to global warming, may be an inherent feature resulting from strengthening warm extremes.”

See also —

Extreme weather and climate change: the connections and impacts

Weather extremes–global warming and polar cold

Questions? Please let me know (engelk@grinnell.edu).