Words on Weather & Climate
Trends in Snow Cover
by CRAIG JAMES
On the morning of January 12, 2011, an amazing 71% of the lower 48 states had at least a little snow on the ground. You can see on this map from the National Weather Service National Operational Hydrologic Remote Sensing Center in Minnesota that Florida was the only state with no snow, although it was not far away. That means at least parts of 49 of the 50 states had snow on the ground since the volcano tops in Hawaii were also snow covered.
Last year on February 12, the same thing happened, although this time there was a little snow in the Florida Panhandle but none in Hawaii, at least not officially. However, upon further investigation, some people supposedly took pictures on that day of a little snow left on the north slope of Mauna Kea, the highest mountain in Hawaii. If that was true, it would have been the first time all 50 states had snow at the same time in living memory. There are no official records of this statistic, but it is indeed a rare event.
Rutger’s University in New Jersey does have a Global Snow Lab, where they keep track of such things as global snow cover and extent. This first graph shows the snow extent (amount of land area with snow on the ground) for the winter months of December, January and February for the Northern Hemisphere since the lab began keeping records in 1967.
The overall trend line shows no change, although there were huge variations from year to year. The greatest snow extent was in the harsh winter of 1978 (when we had our big blizzard) with the least just a few years later in 1981. The snow extent was the second greatest last year in 2010. On the next graph, you can see the snow extent for the spring months of March, April and May.
The trend is definitely down since 1967, which appears to support the claim that spring warm-ups are occurring sooner due to global warming. I certainly have no problem with the idea that the earth has warmed slightly since 1967, but I don’t believe we are anywhere close to understanding how much it has warmed and whether that warming has been caused by CO2 or is mostly due to natural cycles.
I think you can actually draw two approximately 20-year-long horizontal trend lines on the spring graph as I have done; one from the late 1960s to the late 1980s and the other from 1990 until now. If what I believe is correct, the trend over the next 20 years will be back up in the spring.
Craig James has been retired since July 1, 2008, after 40 years of broadcasting television weather. He was chief meteorologist at WZZM-TV for 12 years and chief meteorologist at WOOD-TV for 24 years. He is a graduate of Penn State University, where he received a Centennial Fellowship Award. He was also honored as a Fellow of the American Meteorological Society.