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Holiday Heat is On in Europe, Australia, Eastern U.S.

By: Bob Henson 5:36 PM GMT on December 21, 2015

The year 2015 is is just days away from nabbing the top spot as the world’s warmest in more than a century of recordkeeping. As if to emphasize the point, the year is wrapping up with a blaze of December heat records around the globe. Some of the most exceptional numbers are being tallied over eastern North America, Europe, and Australia, which all ran quite warm in November as well. To be sure, some individual days have been standouts--and there are more of those to come--but the truly striking aspect of this month’s heat is its tenaciousness. We remain in the firm grip of a strong El Niño, as well a strongly positive North Atlantic Oscillation that’s keeping Arctic air on a tight leash at high latitudes.

Figure 1. Departures from average temperature across the contiguous U.S. for the period Dec. 1 – Dec. 19, 2015. Image credit: NWS Climate Prediction Center.

Eastern U.S.: Humidity, warmth, and thunder for the holidays
It’s been an absurdly mild December over most of the United States. Figure 1 shows above-average readings across nearly all of the country. The biggest departures can be seen over the Upper Midwest. However, those smaller departures you see over the Northeast are actually more climatologically significant, because the climate there doesn’t tend to vary as sharply from day to day and week to week. Moreover, chilly air arriving in the Midwest over the next few days should help tamp down the departures there, but not so much in the East. Amazingly, New York’s Central Park has only had one freeze so far, if you can call it that--a paltry 32°F on November 24--and there may be no subfreezing temperatures to come before 2016 arrives. New York is just one of the nation’s big eastern cities likely to streamroll longstanding records for their all-time warmest December. Among the candidates:

These records might not be in such jeopardy if an Arctic air mass were approaching before year’s end. Instead, another slug of unseasonably mild, humid air will be streaming from the tropics across the southern and eastern U.S. later this week. Often when such an air mass approaches in winter, it will glide above an entrenched surface layer of cold air. But with snow cover nil this year, and preexisting Arctic air absent, the tropical surge has a better chance of mixing all the way to the surface. There could be severe weather across the Mississippi Valley on Wednesday, and dew points approaching or topping 60°F will make it feel oddly humid as far north as Boston by Christmas Eve. For millions of people across the southern and eastern U.S., Christmas Eve and/or Christmas Day will be the warmest in living memory, and in some cases the warmest in more than a century of recordkeeping (see this weather.com roundup for more details). Even with the warmth, it may not be the sunniest of holidays, as the rich moisture will swaddle many places in dank clouds and fog.

Even Mount Washington, NH--notorious for its extreme winter weather--may eclipse its warmest December temperature on record (47°F), if the WU forecast of 49°F on Christmas Eve is correct.

Figure 2. Potential record highs on Christmas Day—Friday, December 25, 2015. Image credit: weather.com.

This “warm wave” will extend far into eastern Canada. Temperatures may crawl above freezing at the southern tip of Hudson Bay by Wednesday, and relative mildness should envelop most of the Canadian Maritimes. The town of Churchill Falls, Labrador, has an average daily low of -15°F this time of year; on Christmas Eve, it may struggle to get below 26°F. Montreal and Ottawa are likely to smash records for their warmest Christmas Eve with readings well above 50°F, according to The Weather Network’s “Christmas Eve Blowtorch” outlook. Montreal occasionally gets a non-snowy holiday, but nearby ski areas are struggling because it won’t even be cold enough to make snow.

On the other side of the pond . . .
Across the North Atlantic, the warmth has been equally impressive. Three European nations with records of 150 years or longer--Finland, Sweden, and Estonia--have set or tied all-time national heat records for the month of December in recent days. Earth’s longest-running climate archive, the Central England Temperature Record, has a chance at the warmest December in its 357-year history. The CET average for the month to date (12/1 – 12/19) is 9.9°C, a phenomenal 5.1°C above the 1961-1990 mean and well above the warmest December on record (8.1°C in 1934 and 1974). London Heathrow has made it above 10°C (50°F) every day thus far in December, and that streak may continue through month’s end. Gardeners in Cornwall, England, have reported spring-flowering camellias in bloom months ahead of schedule.

Several other European nations are on track for a record-warm December, including the Netherlands and Germany. New all-time highs for December have been set in a number of capital cities, including Stockholm, Sweden (13.2°C); Riga, Latvia (11.8°C); Tallin, Estonia (11.7°C); and Helsinki, Finland (10.8°C). Nearly 100 stations across Germany have seen their highest daily minima for any December, said Michael Theusner (Klimahaus-Bremerhaven) in an email. “Even though not many all-time highs [for December] were broken, the duration of the warmth and its magnitude are exceptional,” he added. Germany’s monthly anomaly to date--5.4°C above average--is far beyond the peaks of around 4.0°C observed in 1934 and 1974.

Further south, a weekend burst of downslope southerly winds (the famed “foehn”) brought temperatures on Sunday up to balmy values along the northern slopes of the Alps and Pyrenees. These included 17.7°C (63.9°C) at Hohenpeissenberg, Germany and 16.3°C (61.3°F) at Brand, Austria, both at elevations of more than 3200 feet. The town of Pau, France, basked in 25.4°C (77.7°F) warmth. (Thanks go to weather records researcher Maximiliano Herrera for these statistics.) Ski resorts across the Alps are bracing for continued mildness throughout the holidays.

Figure 3. These images, taken exactly one year apart--0920 local time on Dec. 21, 2014 (top) and 2015 (bottom)--show the stark contrast in snow conditions at the ski resort of Grossarltal in central Austria. Image credit: ZAMG, courtesy Maximiliano Herrera.

For a truly toasty Christmas, head Down Under
If it seems just a bit too mild to be wrapping presents or roasting a holiday dinner, consider the hardy souls of Port Augusta, Australia (“Gateway to the Outback”). They had to deal with record December temperatures that vaulted to 47.2°C (117.0°F) on Saturday. For the first time in any December, the city of Adelaide saw four consecutive days of highs topping 40°C (104°F). The torrid air swept into New Zealand on Monday: the South Island city of Dunedin hit a scorching 34.6°C (94.3°F), more than 4°F above its prior December record of 32.2°C. Readings should tumble back to more seasonable levels later this week across Australia, with predicted highs for Christmas Day mostly in the 80s to low 90s Fahrenheit.

Jeff Masters will be back later this week with his definitive roundup of this year’s Category 5 tropical cyclones around the world. In the meantime, if you’ve never heard the voice of NOAA Weather Radio saluting the season, you’re in for an old-school automated treat. The winter solstice begins on Monday night at 11:48 pm EST. Happy holidays, everyone!

Bob Henson

Figure 4. Coping with pre-holiday (heat) stress in Adelaide, Australia, on December 19, 2015, the final day of an unprecedented four-day stretch of December days reaching 40°C (104°F). Image credit: Morne de Klerk/Getty Images.

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The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.