Why it will snow less on cold days in the future

Post date: Oct 18, 2014 6:53:14 PM

Monday, December 31, 2012. When does it snow? If the air is cold enough. Are these conditions always satisfied in Western Europe winters? No! We need a special circulation to bring the cold air to our region. In the future we might need even “more special circulations”. These “more special circulations” (blocking-like conditions) are on average drier than the average circulation in the present climate. We show this in detail in a paper that has just been accepted for publication in Climate Dynamics (doi:10.1007/s00382-012-1583-x).

Projected future change (in %) of average daily precipitation on Hellmann days (days with mean temperature below freezing). Brown colors indicate a decrease, blue colors an increase.

Abstract: “It is demonstrated that the probability for precipitation on days with daily-mean temperature below freezing (Hellmann days) may reduce in western Europe by up to 20-50% near the end of the 21st century, while the average temperature on such days increases by about 1.5 degrees. This decrease of snowfall occurs in addition to the expected 75% decrease of the number of such days. The result is insensitive to the exact freezing-level threshold, but is in sharp contrast with the probability of winter daily precipitation, which increases under most global warming scenarios. Observational records also reveal that probabilities for precipitation on Hellmann days have been significantly larger in the past. The future reduction is a consequence of the fact that the freezing threshold is a more extreme quantile of the temperature distribution in the future than it is today. These low temperature quantiles can only be reached by more extreme circulation types, and for western Europe these have low probability for generating precipitation.”