The United States' smallest meteorologist must be scratching his head about now.
Each February for the past 125 years, Punxsutawney Phil -- the Pennsylvanian groundhog long considered a living symbol of Groundhog Day -- has sauntered from his burrow to cast a shadow on the weeks and months ahead. His predictions, though not always accurate, are cheered by hundreds of fans who flock to his den at Gobbler's Knob, a wooded hillock just outside the town that bears his name.
The ground rules for Phil's tradition have always been clear: If the groundhog sees his shadow, six weeks of winter are yet to come; if no shadow appears, then spring is on its way.
But with cold weather stubbornly absent across much of the Northeast this year and spring seemingly already under way, Phil may have beaten Old Man Winter to the punch. Now it's anybody's guess what a groundhog's shadow may portend.
"NEWS FLASH: Groundhog Day cancelled! Phil says he's pretty sure spring *already* arrived in western PA, preempting tomorrow's event," joked climate scientist Michael Mann in a Twitter post yesterday.
The winter of 2011-2012 is already among the top 20 warmest in historical memory, and is likely to earn a third- or fourth-place record in parts of New York and New Jersey, said Art DeGaetano, a climatologist and professor of Earth and atmospheric sciences at Cornell University.
That conforms to the trend of the past decade, which has seen three of the four warmest winters since meteorological data collection began, he said.
A mixed forecast
Much of the cold that would usually descend across the United States this time of year is trapped in a northern pressure system called the Arctic Oscillation, he said.
The warmer weather patterns have implications for animal species up and down the region, including Punxsutawney Phil and his fuzzy brethren, said Paul Curtis, a professor of natural resources and Cooperative Extension wildlife specialist at Cornell.
Groundhogs are one of the few animals that achieve true, or "profound," hibernation, burrowing down below the frost line for the coldest months of the year. During this period, which usually lasts from mid-October to late February, a groundhog's heart rate drops from 80 beats a minute to only three or four, and its body temperature falls by 60 degrees.
Warmer temperatures shorten hibernation, causing groundhogs to burrow later and rise earlier than is customary, said Curtis.
While this probably won't have a harmful effect on the woodchucks, other species will respond more strongly to the mild weather, with possible implications for humans, he said.
"The big one is deer," he said. "Mother deer emerge from mild winters with a lot more of their body fat still on them, meaning that they're less likely to drop stillborn calves. That can certainly make for a population swell, particularly when you have a number of warm years back-to-back."
Although deer can devastate plant life when their populations grow out of control, the real danger to humans comes from the ticks they carry, said Curtis. Deer ticks spread Lyme disease, a debilitating bacterial infection that can result in symptoms from chronic muscle aches to paralysis.
"We've seen a huge upswing in reported cases recently, from about seven in 2009 to 70 in 2010," he said.
Calm before the snap
There's another danger in the mild weather that might catch even the punctilious Punxsutawney Phil unawares. Plants and animals that have been lured out by the early spring could be caught at their most vulnerable moment by a sudden cold snap, said Curtis.
"When we look across the board, we see birds nesting and frogs calling as much as 20 days earlier than normal," he said. With the winter still undecided, a sudden snowfall could threaten their newborn young, he said.