Future Changes in Northern Hemisphere Extreme Snowfall

While mean and extreme snowfall are projected to decline across many mid-latitude regions, particularly those close to the melting point. An opposing signal is expected in high-latitude and high-elevation regions, including the Arctic. Future changes in Northern Hemisphere extreme snowfall are investigated using KNMI’s Large ENsemble TIme Slice (LENTIS) model. Snowfall changes are closely linked to climate warming. Regional present-day seasonal mean climatological temperatures determine the sign of snowfall change through seasonally dependent temperature turning points. These turning points vary between -11℃ and -18℃ for median snowfall, whereas extreme snowfall exhibits higher turning-point temperatures ranging from -4 ℃ to -11℃ across seasons. As a result, increases in median snowfall event frequency and amount are confined to the coldest regions, while extreme snowfall is already increasing across a wider range of regions with higher climatological temperatures. Under warming conditions, sufficiently cold regions are projected to experience substantially larger increases in extreme snowfall frequency (up to 278%), and amount (up to 271%) than in median snowfall (up to 101%, and 152%, respectively). Regions that approach or exceed the melting point are primarily governed by thermodynamic effects, whereas colder regions remain influenced by a combination of thermodynamic and dynamical circulation changes. As snowfall is likely to influence the surface mass balance of the Greenland Ice Sheet, atmospheric circulation patterns over Greenland are examined in detail. Extreme snowfall over Greenland is found to occur predominantly during a dipole in sea level pressure anomalies spanning Greenland and Northern Europe, which promotes the northward transport of warm, moist North Atlantic air. Using the Greenland Oscillation Index (GOI), which quantifies the strength of this dipole, it is found that the projected increase in extreme snowfall is dynamically driven, with a higher frequency of circulation conditions, characterized by an above-median GOI, impacting particularly Eastern, Central and Northern Greenland. These future increases in extreme snowfall arise from more frequent favorable circulation patterns rather than from an intensification of circulation anomalies.