Philadelphia rides a temperature rollercoaster again, and after hitting another crest, another steep drop comes.
The region has seen an unusual sequence of daily high temperature swings of 20 degrees or more this month – including a sharp drop on Saturday in a wintry weekend that was followed by a sharp jump on Monday to crack to 60 degrees. In terms of temperature swings, this was one of the most volatile months on record.
And despite a few warm days, a cold front is expected to cross the region on Wednesday, with temperatures expected to plummet to 30-35 degrees by Thursday morning.
Get ready for more kick as we head into spring.
What’s going on there? The short answer: It’s that time of year.
Between winter and spring, the behavior of the atmosphere at our latitude is subject to ping-pong between declining and approaching seasons, almost as if trying to figure out which one it wants to be. The first four months are the most choppy time of year for temperatures, according to an Inquirer analysis of National Weather Service data recorded at Philadelphia International Airport.
Take into account the high temperatures, which fluctuate an average of 7 degrees from day to day during these months. But averages can hide a lot. About half the time, the daily maximum temperature is only 5 degrees from the day before. The other half of the time, high temperatures differ more than that.
Sometimes much more.
About one in four days from January to April sees a high temperature 10 degrees higher or lower than the day before.
“It can definitely be crazy and nervous,” said Dave Dombek, senior meteorologist at AccuWeather Inc.
But if volatility is the rule, this month of February is still distinguished by the frequency of these fluctuations.
Normally, temperatures swing 20 degrees or more in a day about once every four weeks. Monday marked the fourth such big change this month. In 148 years of temperature records, less than 2% of the months have experienced as many variations of 20 degrees.
And if temperatures drop 30 degrees or more between Wednesday and Thursday, as expected, this month will see a fifth daily high temperature change of 20 degrees or more. These many big swings in a month have only happened nine times since 1874.
There is a peculiarity of these recordings to note: a high temperature can be recorded at any time of the day, even in the middle of the night. In the steepest overnight temperature drops, the hottest time of day could occur just after midnight, with temperatures dropping for the rest of the night and never recovering.
Whether you’re looking at all-day or just-day high temperatures, the bottom line is the same: lots of volatility this time of year, but this month still stands out.
We’re probably not going to leave this ride anytime soon.
Other factors are at play, but frontal systems are the main drivers of temperature variations.
Each year, Philadelphia and the rest of the northern hemisphere’s midlatitudes are caught in the crossfire between a stubborn winter and an ambitious spring, Dombek and other atmospheric scientists said. Cold and warm air generally remains plentiful in their home regions – namely the Arctic and the tropics – as winter gets long in the tooth.
As the sun rapidly gains strength and the days lengthen in the northern hemisphere – Philly gains more than an hour of daylight from February 1 to March 1 – the warm air becomes increasingly aggressive when ‘it’s heading north and more and more likely to meet resistance.
Strong frontal systems are forming along the boundaries of these contrasting air masses. As they plow from west to east, fronts can pull warm air northward during strong southerly winds and then provide cold air in their wake during gusty northerlies, and that is one of the main reasons for the large temperature variations at this time of year.
So hang on to your hats and make sure you’re strapped in – you can expect more whiplash in the weeks to come.