The trees are swelling with buds, the hellebores are blooming, the soil is as malleable as pudding, and meteorologists are seeing nothing to stop this early-arriving spring from overwhelming the remnants of a remarkably mild and snowless winter.

Monday, when the temperature soared into the lows 70s, was more than a glimpse of the near future, in the view of Bill Cullina, executive director of the University of Pennsylvania’s Morris Arboretum in Chestnut Hill. Winter, he says, has been uprooted.

“It’s go time for spring,” he said. “Lawns are starting to green up. If you’re going to do any lawn fertilization, this is the time to do it.”

Temperatures Monday were about 20 degrees warmer than normal, but well short of the record for the date: 82 in 2016. The rest of the workweek is looking balmy, with a chance of showers on Tuesday.

Things are happening so fast, Cullina said, that the deadline for pruning woody plants like roses and fruit trees is about now: “The window for that is rapidly closing.”

Officially spring will arrive this year on March 19, earlier than it has since 1896; that’s related to astronomy and leap year, not weather. But spring in the horticultural world has been arriving earlier consistently, said Cullina. He estimates that since 1970, the growing season has grown about four weeks on either side of winter.

That warming trend

Various studies have documented the lengthening of the growing seasons, the interval between the last and first frosts, and the winters themselves have lost some bite.

The official average temperature in Philadelphia for the last 30 meteorological winters, the December through February periods, has been a robust 2.4 degrees Fahrenheit higher than it was in the 116 other winters in the period of record.

That is the warmest such period on record.

Just how warm was this winter?

The winter of 2019-20 joined the party with an average temperature of 39.4, 10th-warmest on the all-time list. Although well behind the all-time leader — 43.3 degrees in 1932 — it still was 5.8 degrees higher than the pre-1970 average.

It wasn’t just us. It was the warmest on record in Allentown; No. 2 in Boston; No. 6 in Washington; and No. 7, in New York, according to the Northeast Regional Climate Center.

In terms of lack of snow, all of the above mentioned cities were way below seasonal normals, but Philadelphia was in a rarefied zone with 0.3 inches, No. 2 behind the “trace” of 1972-73 on the all-time snow deprivation list.

So where was the snow?

All winter, storm centers have been passing to the west of Philadelphia. Since winds circulate counterclockwise around storm centers, Philly has been on the warm side of them, thus getting rain instead.

The track has taken storm centers through central New York, the regional climate center’s Art DeGaetano said. Other parts of the country also have been getting their snow. Lake-effect snows of 3 and 4 feet were reported in Upstate New York last week.

According to the Accumulated Winter Season Severity Index, a measure that takes into account the severity and persistence of snow and cold, most of the nation east of the Mississippi River experienced a “mild” winter. The exceptions were northern Michigan, northern New England, and Upstate New York.

West of the Mississippi, several areas are in the “severe” category.

The index doesn’t follow the meteorological calendar, explained Barb Mayes Boustead, a National Oceanic and Atmospheric Administration specialist who created it. She said it was inspired by her desire put the severe winter of 1880-81, the focus of Laura Ingalls Wilder’s novel The Long Winter, in historical context.

The index will keep updating as long as wintry conditions continue, so the winter of 2019-20 in Philadelphia still theoretically has a shot of shaking the “mild” label; late snow’s have been known to happen. But Boustead said it’s a snowball’s chance.

“At this point, it would take an unprecedented amount of snow and cold in the spring months to push Philly out of the mild category for this winter,” she said.

Back to the gardens

Citing dynamic computer models, the government’s revised March outlook has odds strongly favoring above-normal conditions in Philadelphia and much of the nation.

“I would say within the next couple of weeks it’s going to be safe to plant cold vegetables, things like onions and cabbage,” Cullina said.

“Get out there and enjoy it.”