Snow Assessments

2016 Snow Assessment


Aaron Letterly
09 May 2017

Northern Hemisphere Snow Cover


In 2016, annual Northern Hemisphere snow cover extent averaged 24.6 million km2, less than 0.5 million km2 below the 47-year average (Robinson, 2016). Heavy snowfall in October and November led to a September, October, and November (SON) average snow extent maximum over the measurement period. Average snow extent in June through August, while slightly greater than 2015, still ranked among the lowest summer extents and supports the 35-year trend of decreasing Northern Hemispheric snow cover during summertime. Similarly, spring snow cover was very low - March, April, and May all ranked 40th or lower in extent. Total snow cover extent varied 44.1 million km2 in 2016, from a low of 3.0 million km2 in August to 47.1 2 in January. Figure 1 shows the seasonal snow cover over the last few decades.

Figure 1
Figure 1: Three-month average snow cover extent for 1967-2016. December snow extent is taken from the previous year’s winter. Dark lines are individual yearly averages. Colored lines are a 4-point running mean. Three-month averages using months with missing data are not plotted. Data are from Rutgers University Global Snow Lab.

Seasonal Snow Depth Anomalies

Snow depth anomalies derived from the Canadian Meteorological Centre (CMC) daily gridded snow depth analysis (Brasnett, 1999) show the seasonal development of terrestrial, hemispheric snow depth from December 2015 to November 2016 (Figure 2). In December-February, snow across Siberia and the Canadian Archipelago was much deeper than normal. These positive anomalies persisted through May for the northernmost terrestrial Arctic, while Northern Europe and the Rocky Mountains of North America saw decreased snow depths. By the end of the 2016 winter, increased snowfall over isolated parts of Siberia and the Canadian North had once again pushed snow depths above average.

Figure 2
Figure 2: Mean of 2016 seasonal snow depth anomalies for three-month periods in the Northern Hemisphere. Greenland and marine snow depth anomalies were screened out at the suggestion of the data provider. Data are from the National Snow and Ice Data Center (NSIDC).

Snow Extent and Arctic Sea Ice

Feedback cycles in the cryosphere can have dramatic effects on Earth’s radiative budget and can significantly contribute to climate change. Terrestrial snow cover and sea ice are two of the Northern Hemisphere’s most reflective surfaces. Sweeping changes in the amount of these surface types affects the amount of solar radiation absorbed, triggering a change in temperature. Since the beginning of the satellite record, the decreases in annual minimum extent of snow cover in June and sea ice in September have pointed towards a warming Arctic. Though the inter-annual variability of snow cover extent is greater than that of ice, the 4-year running mean shows that minimum snow and ice extents have been decreasing at approximately the same rate since around 2001 (Figure 3).

Figure 3
Figure 3: Time series of Arctic sea ice and snow cover extents, indicated as annual values and 4-year running means.

References

Derksen, C., and R. Brown, 2013: Arctic – Terrestrial Snow [in “State of the Climate in 2012”]. Special Supplement, Bull. Amer. Meteor. Soc., 94(8), August 2013, S132-S133.

Derksen, C., R. Brown, L. Mudryk, and K. Luojus, 2015: Arctic – Terrestrial Snow. [in "State of the Climate in 2014"]. Bull. Amer. Meteor. Soc., 96(7), July 2015, S133-S135. (http://www.arctic.noaa.gov/reportcard/snow_cover.html)

Robinson, David A. – Northern Hemisphere Continental Snow Cover Extent: 2016 Update. Rutgers University Global Snow Lab. (http://climate.rutgers.edu/snowcover/files/Robinson_snowdata2016.pdf)

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