Weather 101 - U. S. National Snow Cover Sets Record

Although records have only been kept since early 2003, snow cover across the United States and the entire Columbia River Watershed (including the that portion in southwestern Canada) has broken a record. As of the morning of January 31, 2010, snow cover was set at 69.7%. This breaks the previous record areal coverage of snow, sleet and ice cover set on January 30, 2010 of 67.7%. It also tops values established at the end of December 2009 - 65.0% on December 30 and 63.0% on December 25.

The snow cover as of the morning of January 31, 2010 is shown in Figure 1. It is easy to see the track of the southern snowstorm from the past few days (examiner links). This storm has significantly added to the snow cover, increasing it by more than 65% over a period of just a few days.

According to Chris Bovitz, a scientist at NOAA's National Operational Hydrologic Remote Sensing Center (NOHRSC) in Minneapolis, MN, it's important to understand how this snow cover analysis is obtained. I couldn't agree more. Transparency of process and data and sharing of information is what makes science believable and understandable.

Understanding the snow cover mapping

The analysis is actually "modeled" snow cover, and according to Bovitz, "is subject to the same limitations that any meteorological model has." NOHRSC uses a 1-kilometer grid and presumes a grid box as "completely covered" with snow if the grid has at least 1 millimeter of snow water. This means that on the edges of the analyzed snowpack, there might only be a small part of a grid box covered by snow. Hence, even though the process is consistent, the areal extent is more likely an overestimate.

NOHRSC adjusts the snow coverage with a data assimilation process when the need arises. Hence, Bovitz notes, "We frequently compare the modeled snow cover to observations, and when differences are large enough and a coherent pattern is evident, we adjust the model closer to observations. In most cases this doesn't affect the coverage, but sometimes this results in snow added to bare ground or the complete removal of snowfall in areas where there shouldn't be snow."

There are also possible adjustments concerning sleet, freezing rain and even hail (the latter not a real problem in winter).

Nonetheless, it is pretty amazing that the snow cover across the U.S. is so extensive at this time in winter. That's because February and March are often times for major snowstorms as atmospheric moisture increases, while cold air is still at play.

Consequences

This has some potential consequences. First, snow cover is potentially a plus for the winter wheat crop, because snow insulates the ground and the seeds. But, if snow melt is rapid and extensive, is affected by heavy late winter rains, melts over deeply frozen ground and/or melts and runs off into still frozen or ice-jammed waterways, flooding could result. This is almost a given in the Red River Valley of the North where the water flows northward into Canada. And according to the NWS in Fargo, "...conditions are developing for significant spring flooding" in the southern Red River Valley.

Snow cover also lowers the albedo or reflectivity of the Earth's surface. This can lead to (as it has done already) toward lower temperatures. Snow is also an excellent radiator of energy, again leading to lower temperatures.

The economic impacts of the snow and cold, in terms of transportation, snow removal and energy use, have already been widely reported in the media (see links at end of this article).

Climate Change or Not?

Is this the start of global cooling (or the end of global warming)? I'm not sure. But it does highlight the variability of weather (as compared to climate). In fact, just examining the two graphs shown in slide shown here - one re past 7 years on 1/31 and the other all of January 2010, it's quite easy to see this variability. Slides showing this variability for January 31 the past 7 years will be posted shortly at (link).

Climate varies, too. It always has and always will. Ice sheets have advanced and retreated; sea levels have risen and fallen; and ecosystems have evolved in response. It's just that climate change occurs on scales of hundreds of thousands of years and longer.

This is stark contrast to Ben Bova's guest commentary in the Naples Daily News (January 31, 2010), in which he notes, "...the usually cold weather experienced by the eastern half of the country (in early January 2010 - my words for clarity) certainly shows that the climate is changing."