Snows of Christmas past
Like many people do at this time of year, the Climate.gov communications team has spent some time reminiscing about the holidays of our childhoods. Many of us wondered whether we could trust our memories of how snowy the holidays were when we were kids compared to now.
So, just for fun, we asked the experts at the Rutgers Snow Lab to show us what their data (based on NOAA satellite images) had to say about whether the U.S. snow extent during the week of Christmas has changed at all in the past 50 years. Fortunately, the team was in the holiday spirit, and they made some time to run a little analysis for us.
The map at right shows the change in the average number of snow-covered days between the 1990-2013 decades and the 1966-1989 decades for the week of Christmas —in other words, the most recent two decades of the time series minus the first two. Places where the ground was snow-covered up to 25% more frequently in recent decades are colored in shades of blue, and places that were snow-covered up to 25% less frequently are colored shades of brown.
According to the Rutgers’ folks, there seems to have been a modest increase in snow extent during the holiday week today compared to the past for the country as a whole, although it clearly varies a lot from place to place. Further, the scientists emphasize, singling out a particular winter week for scrutiny isn’t especially meaningful as an indicator of long-term climate change. (Editor’s note: Still, it’s nice to know that sledding may still on the agenda over winter break!)
When it comes to meaningful indicators of how snow has changed over time, the scientists say, it’s best to stick to monthly or seasonal averages. By those indicators, says David Robinson, who leads the Rutgers snow lab project, the pattern is clear: Northern Hemisphere snow cover is declining significantly at the end of the cold season (spring/early summer).
This pattern of snow disappearing earlier in the spring makes intuitive sense with respect to global warming. As temperatures rise, the impact on snow cover is likely to show up first in those seasons where the temperature is just barely cold enough for snow. Reductions in snow can also feed back on the atmosphere, amplifying warming. Where winter temperatures are well below freezing, however, temperatures will have to rise more significantly before snow cover is affected.
To read more about the state of snow cover in North America and around the world, please see our recent update based on the 2014 Arctic Report Card or a post from earlier this year based on the 2013 State of the Climate report. To see maps of monthly and weekly snow extent since satellite records began in 1966, please visit the Rutgers Snow Lab website. Daily snow totals, depth, and other snow analysis are also available from NOAA’s National Climatic Data Center.