Last week began with a historic Arctic outbreak that brought the most frigid air in decades, overwhelming Texas’s power grid and plastering the South with snow and ice. As this week ends, most of the Lower 48 has seen a surge of warmth and, suddenly, spring is in the air.

“A phenomenal weather shift,” is how Tom Skilling, chief meteorologist for Chicago’s WGN television affiliate, described it, detailing “stunning” temperature swings of up to 90 degrees and snow melting “at an incredibly fast rate.”

Some of the same places that were 50 degrees colder than normal 10 days ago are now running 20 or more degrees above normal.

“The unusual nature and the speed with which warming’s taken hold has been something to see,” Skilling wrote on his Facebook page.

Trees are budding and flowers blooming in the South as vegetation responds to the sudden onset of springlike weather.

The warm-up has virtually eradicated the snowpack in some winter-weary cities, such as Chicago, where at least two-thirds of it has vanished in just over a week.

The same weather pattern could bring heavy rainfall and potential flooding to parts of the South and Southeast, with severe weather becoming a concern deeper into March.

A major warm-up

With widespread warmth over the Plains and Midwest, it’s hard to believe that hypothermia was a concern last week, when dangerously cold temperatures and wind chills down to 50 below targeted parts of the central United States.

Dallas dropped to minus-2 during the outbreak, while Oklahoma City plummeted to minus-14 — its coldest reading since 1899. Austin fell to 6 degrees, the coldest since 1949. Houston’s Intercontinental Airport got down to 13 and Brownsville to 22, both the coldest in more than 30 years.

This week has been a different story, with summerlike highs in the 80s in each of the major Texas cities. Oklahoma City recorded an 86-degree warm-up in one week’s time. In Amarillo, Tex., it was an 88-degree leap.

The same has been true across the central and northern Plains. Minneapolis, which saw temperatures in the negative teens nine times this month, hit 40 on Monday for the first time since Christmas. That’s a 60-degree jump.

Kansas City, which hit minus-13 last week, made it to 69 degrees Tuesday. And some places, like Valentine, Neb., have seen temperature swings of 100 degrees or more this month.

Looking ahead, it appears that above-average temperatures will likely continue into mid-March, especially over the central and eastern U.S.; NOAA’s Climate Prediction Center highlighted odds of anomalously mild temperatures lasting well into the middle of spring.

Mild temperatures devour snowpack as temperature roller coaster settles

The insurgence of warm air spreading over the country has devoured much of the nation’s snowpack. It dropped from a record high areal coverage of 73 percent of the contiguous United States to 30.5 percent as of Friday.

Chicago’s snowpack has dwindled from 21 inches on Feb. 16 to barely seven inches as of Friday morning. At least a foot of snow was present on the ground for 15 consecutive days beginning Feb. 9, marking the city’s fourth-longest streak on record.

Before the onset of bitter cold, winter was shaping up to be a cake walk across the Midwest and Corn Belt — Chicago was five degrees above normal in both December and January, but is averaging more than nine degrees below average for February. In Des Moines, December and January were three to four degrees above average, with the mercury plunging 14 degrees below normal in February.

A changing weather pattern ushers in spring as flowers bloom

The bitter cold pattern in early to mid-February, ignited by an early January disruption to the polar vortex, was characterized by a sharp dip in the jet stream over the central United States. Frigid Arctic air surged south from Canada in response, spilling all the way to Mexico and the Gulf Coast. It unleashed the coldest weather since 1989.

Along the periphery of the cold air, waves of wintry precipitation swept across the country. Abilene, Tex., set an all-time snowfall record with more than 15 inches, while damaging bouts of ice slammed the Mississippi and Tennessee valleys.

Since then the jet stream has bent north, allowing a dome of warm air to build over much of the country. That will also induce a drying trend over the Rockies, Texas, the South and parts of the East Coast, with above-average precipitation predicted in the Ohio Valley.

In its wake, spring has engulfed the southern United States, prompting leaves to emerge and flowers to bloom.

“Spring leaf out has arrived in southern states,” wrote the National Phenology Network on its website. They wrote that last week’s cold contributed to delaying spring by a week or so in Florida and South Texas, but much of the South has seen spring arrive a week or two early.

What to expect late February into March

The weather pattern will remain mild, on balance, over the Central U.S. as March begins. However, Arctic fronts will still occasionally sweep south out of Canada and, as they interact with milder air steered north from the Gulf of Mexico and Atlantic Ocean, stormy weather characteristic of the season can be expected.

In the coming days, high pressure east of the Bahamas will draw southerly winds over the Southeast, pumping moisture ashore and setting the stage for heavy rains from Arkansas, Louisiana and East Texas along the Interstate 40 corridor into Tennessee and the Carolinas. Northern Alabama, Mississippi and the Appalachian foothills of Georgia will also probably see heavy rainfall. Some places could pick up three to five inches by the middle of next week.

Already, the National Weather Service Weather Prediction Center is calling for a slight risk of excessive rainfall and flash flooding, writing “moisture from the Gulf of Mexico will pool along the boundary, aiding in producing heavy rain … Sunday that will taper off on Monday.”

“These rainfall amounts could cause flooding in some areas, along with likely rises on area rivers and lakes starting Sunday and lasting into next week,” wrote the Weather Service office in Nashville.

Meanwhile, the upcoming pattern may harbor an uptick in severe weather potential, particularly across the Deep South and Southeast by the second week of March.

Jason Samenow contributed to this report.