Snow Assessments

Ross Brown (ECCC) and Kari Luojus (FMI)
3 June 2018

Northern Hemisphere Snow Cover

Early 2018 experienced close to record maximum snow accumulations over Northern Hemisphere and Arctic land areas since satellite passive microwave coverage began in 1979. The Finnish Meteorological Institute confirmed that the 2017/2018 winter has been quite exceptional compared to typical recent winters (Figure 1), and is one of the snowier winters in the period since 1979 where passive microwave satellite data have been used to monitor the amount on snow on land. While 2017-2018 is not a record - that title belongs to 1993 with 3649 gigatons of peak snow water storage - close to 3500 gigatons of peak snow water storage were estimated, which ranks as the tenth highest peak snow accumulation since 1979. However, the mean March snow mass of 3190 gigatons for this winter ranks as the highest measured since 1979 in terms of a monthly mean. The peak period of snow accumulation typically occurs in March over Northern Hemisphere land areas.

Figure 1: The GCW snow water equivalent (SWE) tracker for winter 2017/2018. The SWE tracker is based on the GlobSnow SWE product by the Finnish Meteorological Institute (FMI).

Another source of information on seasonal snow water storage is the Canadian Meteorological Centre (CMC) operational daily snow depth analysis, which uses real-time surface snow depth observations and estimated snow accumulation from a snow model driven by forecast and analysed precipitation and air temperature data. Environment and Climate Change Canada confirmed that 2017-2018 was also an exceptional snow accumulation winter with the CMC product showing the highest annual maximum snow accumulations over Arctic land areas since the analysis was initiated in 1998 (Figure 2).

Figure 2: Estimated Arctic (north of 60°N) land area snow water storage (Gt) from CMC operational daily snow depth analysis. The series are corrected for an artificial positive trend related to the increasing resolution of the precipitation forecast used to drive the snowpack model that generates the first-guess field.

The factors contributing to the above-average winter snow accumulations were colder than average winter air temperatures over northern hemisphere mid-latitudes, and above-average winter precipitation over Europe, Scandinavia, eastern Siberia and Alaska. Spring air temperatures were also 2-4°C below-average over large regions of Arctic land area which contributed to above-average snow depths in early May (Figure 3).

Figure 3: Snow depth departures (cm) between May 7, 2018 daily snow depth and the average value over the 1998/1999 to 2011/2012 time period. Areas where the current snow depth is within ±5 cm of the historical average are shaded gray. The thick red contour line indicates the historical location of the snowline (50% probability of snow depth ≥2 cm).

The results highlight the strong interannual variability in snow cover, which responds quickly to year-to-year variations in atmospheric circulation and corresponding anomalies in air temperature and precipitation.