This Groundhog’s Day Punxsutawney Phil may see his shadow which would indicate 6 more weeks of winter and likely more snow, according to legend in the Pennsylvania town, but a NASA satellite confirms that it has already been snowier than usual this winter.

“Composite data from NASA’s Terra satellite show that this winter brought more snowcover in the early part of the season than average,” Dorothy Hall of NASA’s Goddard Space Flight Center said. Results from the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard NASA’s Terra satellite clearly observed more snowcover in the Midwestern and western United States in November and December.

Hall noted that results from MODIS show that, “Snowcover was greater than average in the western and Midwestern portions of the country for the month of November.” Complementing the snowfall were record cold temperatures for November and December 2000 throughout the United States, according to the National Oceanic and Atmospheric Administration (NOAA).

The continental snowline in November 2000 was considerably farther south than its average position as determined from NOAA’s Environmental Satellite, Data, and Information Service (NESDIS) records. NOAA/NESDIS’ average monthly snowline is based on satellite-derived snow-cover products that have been available since the 1960s.

In November the average snowline runs north of the U.S.-Canadian border except in the Rocky Mountains, where it dips to the south and extends all the way into northern Arizona and northern New Mexico. Hall noted, “While the snow extent in the northeastern part of the country was not particularly unusual, by mid-November in the Midwest and the western states, the snow cover was far greater than normal as the snowline extended through the Dakotas south into Nebraska.”

In the west, snow covered large parts of Colorado, Utah and even parts of Nevada, providing banner conditions for ski resorts, which had most of their trails open by Thanksgiving. This winter’s increased snowfall was a nice change for the ski areas that suffered from last year’s lesser snowpack.

NOAA/NESDIS has been producing weekly snow maps of the Northern Hemisphere land surfaces since 1966 using visible-band satellite imagery. Because snow has such a high reflectivity compared to other surfaces on Earth, snow covered areas appear much brighter in satellite imagery than most other surface types. However, Hall noted that the key difference between the MODIS-produced snow maps and the images produced by NOAA/NESDIS is that “MODIS has a higher resolution and an improved ability to discriminate between snow and clouds.”

In the MODIS composite image for the week of November 16-23, 2000, the black line is the average snow line for November and the white area is snow cover. Clouds appear darker than the white snow.

More than 40 percent of the Earth’s land surface in the Northern Hemisphere can be covered with snow during the winter months. The highly reflective nature of snow combined with its large surface cover make it an important factor in the Earth’s radiation balance, which includes incoming solar energy and energy reflected back into space. Because the Earth is in a steady-state balance of incoming and outgoing energy, its temperature undergoes small change, but the mean temperature stays nearly the same. According to the National Snow and Ice Data Center, snow may reflect up to 80 and 90 percent of incoming solar energy, whereas a surface without snow would only reflect 10-20 percent. Retained solar energy means increased warmth.

Many areas of the world rely on the snowmelt for irrigation and drinking water. In the western U.S, mountain snowpacks contribute up to 75 percent of all year-round surface water supplies. Therefore, it is necessary to monitor snowpacks closely throughout the winter and spring for assessment of water supply and flooding potential, and MODIS data will prove useful in this capacity.

As an instrument on NASA’s Terra satellite, MODIS continuously observes the Earth’s surface in a sweeping motion, every 1-2 days with a scanning imaging radiometer. Its wide field of view (over 2,300 kilometers or over 1,429 miles) provides images of daylight-reflected solar radiation and daytime and nighttime thermal emissions over the entire globe. Sample MODIS imagery is available at:

Terra was launched on December 18, 1999 and began collecting data on February 24, 2000, part of a 15-year global data set on which to base scientific investigations about the Earth.

Snow and ice products generated from MODIS data include daily and 8-day composite snow-cover maps, including lake ice on large inland lakes, daily and 8-day composite sea ice-cover maps, and sea ice-surface temperature maps. There will also be global daily and 8-day composite map products available for climate modeling. These products are archived at the National Snow and Ice Data Center (NSIDC) in Boulder, Colorado.

MODIS images of the snowcover in the Midwestern and western United States can be found at: