Betting on a White Christmas, U.K.-Style

Millions of Americans watch and wait for the potential of a white Christmas each year, but in the United Kingdom, people put their money where their forecast is. Unlike the United States, betting on weather events is legal in the U.K., and snowfall on Christmas Day is just one of the many atmospheric phenomena on which Brits can place bets. In April 2011, for example, one betting firm was offering 4-to-11 odds that Britain would be hotter than the Mediterranean holiday island of Ibiza on an upcoming holiday weekend, and 3-to-1 odds that it would rain in London during the royal wedding of Prince William and Catherine Middleton. Last Friday, nine days before Christmas, bookies set 8-to-1 odds that London would see snowfall on December 25, meaning that bettors would collect $8 for every $1 they bet on a white Christmas. That prospect looks very unlikely now, with temperatures expected to approach 60°F (16°C).


Figure 1. Rooftops of houses in the town of Luton, England, are covered with snow on December 22, 2009. Heavy snowfall resulted in cancelled flights and train trips across the country. Image credit: Oli Scarff/Getty Images.

A snow-frosted British Christmas: more fable than fact
Those who dare to bet on snow in London for Christmas will usually be disappointed. Our image of a snowy England during the holidays was largely the doing of Charles Dickens, author of “A Christmas Carol.” When Dickens was growing up in London during the 1810s, near the tail end of the Little Ice Age, there were reportedly six white Christmases in just a decade’s time, and this experience likely colored his later writings. Actually, snowfall across England is more likely to occur in January, February, and March than in December, thanks to the delay in winter cooling produced by the surrounding ocean. Another factor that made white Christmases even more common in England prior to 1752 was a timekeeping quirk. The British changeover from the Julian to the Gregorian calendar meant that Christmas suddenly moved up by 12 days relative to the winter solstice, which pushed the holiday away from the climatologically snowier period that occurs well after the solstice.

In our warmer 21st-century climate, snow cover at Christmas is fairly uncommon across the British Isles. The UK Met Office defines a white Christmas as when at least one snowflake is observed between midnight and midnight on December 25 (no accumulation required). By this definition, most years produce a “white Christmas” at least somewhere in the UK, but only 4 of the last 52 years have produced widespread snow cover (defined as more than 40% of UK stations reporting snow on the ground at 9 AM). Two standouts in recent years were Christmas 2009 and 2010, both of which saw widespread snows of a few inches and a solidly white Christmas in many areas. A total of 83% of British observation sites reported snow on the ground in 2010, which is the largest coverage for any year in reliable snowfall records that date back to the 1960s. In contrast, 2015 saw the UK’s warmest December on record, with no snow cover anywhere in the nation on Christmas Day (although it still counted as a white Christmas on the national scale because 10% of stations reported at least a flake falling).


Figure 2. Britain was almost completely snow-covered on January 7, 2010, following days of heavy snow. Image credit: Jeff Schmaltz, MODIS Rapid Response Team, NASA/GSFC, via Wikimedia Commons.


Figure 3. Historical odds of a white Christmas, in percentages, based on data from 1981 to 2010. Image credit: NOAA.


Figure 4. Predicted departure from average temperature (in degrees °C; multiply by 1.8 for degrees °F) for 18Z (1:00 pm EST) Sunday, December 25, 2016, as projected by the GFS model run at 12Z Wednesday. Below-average readings will predominate west of the Rockies, with afternoon temperatures up to 20°F - 25°F above average in the central states. Despite the mildness, most areas should end up falling short of record highs, especially in parts of the East Coast where Christmas Day 2015 was by far the warmest on record. Image credit: tropicaltidbits.com.

The U.S. white-Christmas outlook: not too far from climatology
As of Wednesday, the odds for a white Christmas 2016 in the United States are fairly close to what one might expect: highest in the mountainous West and along the northern tier of states, where recent storms have already dropped a decent snowpack, but virtually nil from the central Plains to the Eastern Seaboard and southward. As a strong upper-level storm approaches the central states, mild air will be pumped north across the lower- and mid-Mississippi Valley. Instead of snow, severe thunderstorms could erupt on Christmas Day across parts of the Southern Plains, especially Oklahoma, according to the long-range outlook issued Wednesday by NOAA's Storm Prediction Center. Further north, a swath of heavy, windblown snow will likely shift from Wyoming and Montana across the Dakotas and into northern Minnesota from Sunday into Monday. Many of the nation’s largest cities in the East, Midwest, and South saw their last white Christmas in either 2009 or 2010, which were harsh winters in the U.S. as well as Britain.

You can find up-to-the-minute forecasts of where snow is expected over the holiday weekend, plus lots of additional background, at a special weather.com page.

The Weather Company tops new analysis of forecast accuracy
A major analysis of more than 139 million forecasts issued by public and private firms in the United States, Asia-Pacific, and Europe finds that those from The Weather Company, an IBM Business (which includes Weather Underground), come out on top. The study, produced by the U.S.-based verification firm ForecastWatch, examined the percentage of high and low temperature forecasts that fell within 3°F of the observed noon-to-midnight highs and midnight-to-noon lows, as well as the percentage of time that icons predicting precipitation or no precipitation on a calendar day were correct. The Weather Channel (via weather.com) and/or Weather Underground showed the greatest accuracy for 34 out of 45 regional and lead-time groupings in the study, which spanned time periods from 2010 to mid-2016 for the U.S. and 2013 to mid-2016 for Asia-Pacific and Europe.

“Our users and clients turn to us to help them make weather-related decisions with confidence. This study shows The Weather Company as the undisputed accuracy leader, confirming the trust of more than 250 million people who choose The Weather Company for weather information every month,” said Mary Glackin, senior vice president of science and forecasting operations at The Weather Company. “Making a claim is easy, but backing it up takes continued effort and focus on who you’re serving. With IBM, we’ve stepped up investment and made a dedicated effort toward advancing our forecasting skill in 2016.”

See the IBM news release for more on the forecast technologies used by The Weather Channel and Weather Underground, as well as a link to the full analysis from ForecastWatch. We’ll be back on Friday with a new post.

Bob Henson


Figure 5. David Karnovsky, general counsel for the New York City Department of City Planning, cross-country skis down West 73rd Street towards Central Park on December 27, 2010. A blizzard that pounded the U.S. East Coast delivered 20 inches of snow to New York City while snarling post-Christmas travel. Image credit: Andrew Burton/Getty Images.