Wednesday Supplemental Summary

DATASTREME SUPPLEMENTAL SUMMARY

To complement the Daily Summary for Wednesday, 5 December 2001

DREAMING OF A WHITE CHRISTMAS

One of the special memories associated with the upcoming holiday season is the experience of a white Christmas. So can we expect a white Christmas this year? This question is often asked not just by residents across the northern portion of the country. While a major snowstorm would be viewed as a major inconvenience by most holiday travelers, many people secretly hope for "some of the white stuff" on Christmas morning. This dream has been ingrained in many holiday traditions, ranging from the scenes on the Christmas cards to the theme of the popular song "Dreaming of a White Christmas" made famous by Bing Crosby in the 1940's.

So what is a white Christmas? Traditionally, this event occurs if an inch or more of snow cover (snow on the ground) is measured at an official observation station as of 6:00 AM CST - which is 1200Z, the primary "synoptic" observation time when the depth of snow cover is typically measured.

How often does a white Christmas occur? Did you know that climatological statistics are kept for the probability of a white Christmas? Based upon statistics that have been collected from 340 first order stations for the standard 30 year climatological reference interval between 1961 to 1990, the National Climatic Data Center produced a national map that shows the ratio of the number of times that a particular station experienced a white Christmas during the interval as a probability. For example, Des Moines, IA had only 15 Christmases between 1961 and 1990 when an inch or more snow cover was observed, so the probability that residents of Iowa's capital city would have a white Christmas is 50%.

Across the nation, some locations are almost certain to have a white Christmas. These places can be found along the Canadian border surrounding the Great Lakes, such as International Falls, MN and Marquette, MI (both with 100%) and in New England, such as at Caribou, ME (97%). Stations at higher elevations in the Rockies also have a higher probability, such as at Flagstaff, AZ with a 56%. Sites close to the oceans typically have a lower probability as the oceans tend to be relatively warm at this time of year. Thus, some coastal Alaskan stations have less than a 50% probability. Santa typically finds tough sledding on his journey to that half of the country south of latitude 40 degrees that is not mountainous, where chances of a white Christmas fall from 50% to 20% or less.

You can monitor the current snow cover across North America using a snow chart that is based upon satellite data.

Have a happy and safe Holiday Season!