Spring ordinarily is a much-anticipated season around here. But at 11:54 a.m. Friday, one of the wildest springs in the period of record will come to a more-than-welcome end with the official arrival of the astronomical summer.
Already, the National Weather Service in Mount Holly has issued 138 severe-thunderstorm warnings this year through Thursday, compared with 33 in the same period last year, said Joe Miketta, the warning-coordinator meteorologist. It also has dispatched 23 tornado warnings; last year, 2.
“We’re not just making them up,” Miketta said. “There’s a lot of weather going on.… We’re not trying to scare people."
A major break in the atmosphere’s misbehavior will coincide with the arrival of the astronomical summer Friday as the rain chances evaporate. However, wind gusts up to 40 mph will challenge trees situated in saturated roots, Miketta warned. A comparatively spectacular dry and warm weekend is due to follow, but a rinse-and-repeat cycle could return at the beginning of the workweek with showers in the forecast Monday and Tuesday.
For weeks, the region has been caught in a pattern that in winter might produce snow. Climaxing with more than a month’s worth of rain late Wednesday night and Thursday, this spring has yielded a harvest of severe weather, flooding, gloom, sleep-ambushing iPhone alerts, and assorted warnings of mayhem.
It actually has been wetter in years past, but Tony Gigi, who would pay more attention to these things than most of us, offers one unofficial measure of how wet it has been.
“I can tell you there hasn’t been one day so far this year that I have been able to mow the entire lawn without leaving mud ruts,” said Gigi, a former National Weather Service meteorologist who lives in Mount Laurel and helps run the phillywx.com discussion board.
It’s not as though it rained every day, just more than half of them. It’s not as though the sun went AWOL completely. Philadelphia typically has six or seven officially “clear” days a month in spring; it has had a grand total of six since the spring equinox on March 20.
But data don’t quite capture what’s been going on. The region likely has set some kind of record for watches, warnings, advisories, and scare alerts, some of them warranted.
Pennsylvania has also had at least 25 confirmed tornadoes so far, says Pennsylvania State University’s Kyle Imhof, the state climatologist. The average for an entire year is 13. New Jersey has had three; annual average, two.
Perhaps surprisingly, only two daily rainfall records were set in Philadelphia, and those occurredWednesday and Thursday. And while June already has earned an elite place for precipitation, the record for total number of days with measurable rain appears to be out of reach, and a monthly rain record would be a long shot.
So far, 7.71 inches has fallen in June in Philadelphia; the record is 10.56, set in 2013, followed by 10.08 in 1938. Measurable precipitation — defined as 0.01 inches or more — has fallen on half the June days; the record, at least dating to 1872, when current record-keeping began, was 18 days in 1972.
Close to 17 inches has fallen officially since March 20; better than a half-foot above the long-term average.
While it has been rainier in past years, the recent deluges argue in favor of the so-called enhanced precipitation signal; various studies have attributed heavier rains to worldwide warming. A warming atmosphere theoretically holds more moisture.
In the shorter term, meteorologists say the East has been under a broad area of a trough, or lower pressure in the upper atmosphere that is conducive to clouds and rains. This is a by-product of a pressure pattern over the North Atlantic that promotes storminess in the mid-Atlantic and Northeast, said Gigi. In winter, such an alignment might be a reliable snow-maker.
The trough and an area of heavier air or high pressure to the south has set up a battleground across the East and Midwest. “We remain in the squeeze play,” said Gigi.
“We’re kind of on a boundary,” said Miketta. “When you’re on the boundary line, that’s when the active weather occurs. It’s just a bad year.”
In winter, strong temperature contrasts drive winds that move weather systems; as the weather warms, the contrasts weaken and so do the winds. As a result, wet patterns can linger for days and weeks.
A highway of moisture has set up from the Northern Plains to the East, said Paul Walker, senior meteorologist with AccuWeather Inc. “It’s hard to break down the pattern,” he said.
In this case, the pattern break will coincide with an astronomical event: the summer solstice. A strong front finally was due to crash through the region late Thursday, setting off a farewell round of severe weather, forecasters said.
The weekend should be splendidly sunny and dry, and not just rain-free, but outright comfortable. Said Walker, “You won’t have to wring your shirt out when you go outside.”