Baltimoreans can chalk up last year's weather to the law of averages.
The first three months of 2015 were below freezing more often than not, the coldest start to any year here on record. The year ended with a different distinction: a record-warm December so mild it felt more like April.
On balance, it was an average year with some stark contrasts for a region used to weather swings.
Globally, 2015 has been anything but average.
It is all but certain to end up as the warmest year in a 136-year-old record book, breaking the mark set just a year ago. Already, 14 of the 15 warmest years on record have occurred since 2000, according to the World Meteorological Organization.
Climate scientists attribute this year's record in part to an El Nino climate pattern that developed in the Pacific Ocean late last winter. El Nino years tend to be warmer than normal. But it also follows a long-term warming trend.
"As we move into the future, record-warm years are more likely to occur than not," Jake Crouch, a climate scientist for the National Centers for Environmental Information, told reporters last month.
Though the final data on the year's temperatures and precipitation across the globe is not expected until early in the new year, December would have had to set a new record as the coldest ever — and by a wide margin — to keep the global average temperature below the 2014 record.
"It's impossible," Crouch said. "That's not going to happen."
It is also forecast to be one of the warmest years for the 48 contiguous states. Through November, this year was fifth-warmest for the Lower 48. If the mild weather that has dominated the eastern United States the past two months outweighs the cold and snow in the West, 2015 could rise to as high as second.
Taken broadly, local conditions were unremarkable. The average temperature at Baltimore-Washington International Thurgood Marshall Airport was expected to end up around 56 degrees. That's only a few tenths of a degree above the long-term average. Precipitation at BWI has been above normal at more than 51 inches through Tuesday — a rainfall surplus of about 9 inches. But 2014 was an inch wetter, and 2011 wetter still.
Still, there were noteworthy extremes within that data. Baltimore set half a dozen cold-weather records in February and March, said Paul Walker, a senior meteorologist for AccuWeather.com. Parts of the Chesapeake Bay froze over for a second consecutive winter.
Over the summer, June was the wettest on record, with more than 13 inches sprinkled throughout the month. But Rich Foot of the local meteorology website Foot's Forecast noted that any taste of triple-digit temperatures was noticeably lacking. BWI has gone nearly 31/2 years without hitting 100 degrees.
November and December saw another batch of records — in this case, for unprecedented warmth. BWI surged into the 70s three times in November and five times in December. November saw one 80-degree reading.
"That's incredible warmth," Walker said.
It has been baffling to many — including Mother Nature.
"We see daffodils up," said Melissa Grim, chief horticulturist for the Baltimore City Department of Recreation and Parks. "It's a little early for that."
Crape myrtles died early this year and evergreens were burned by the cold, she said. If warm weather sticks around, it could allow Grim and her colleagues to renovate flower beds or perform other maintenance chores that had to be put off last winter. But a rapid switch from mild to frozen could cause more damage, she said.
As any experienced Marylander knows, such fluctuations are common. The Appalachian mountains and Chesapeake Bay have strong influences on local weather, as does the state's place midway between polar air and tropical warmth.
"There's a lot of variation that's just inherent to our geographic location," said Jeff Halvorsen, a professor in the University of Maryland, Baltimore County's geography and environmental systems program. "It actually has very little to do with long-term climate."
But there are questions about whether climate change is making the swings more extreme.
One theory suggests that a warming North Pole is weakening the jet stream, the highway of fast-moving air that carries weather across the country from west to east. It is strongest when there is a big difference in temperatures on either side of it, Halvorsen said, but when it's weak, it is more prone to dip or curve, often bringing unusual weather with it.
Still, Halvorsen warned, it's difficult to link isolated weather extremes and larger climate change. Weather happens on scales of days or even hours, while climate is measured in decades or centuries.
The December warmth could soon seem a distant memory. Long-range outlooks suggest a cold snap by late January, Foot said.
That's not anything unusual — that's just winter.
But given the undeniably rising global temperatures, scientists are eagerly investigating what implications there might be for wild weather swings to come.
"There is something statistical happening on the long term that you can take to the bank," Halvorsen said.
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