Hundreds of Thursday flights were canceled and towns declared emergencies in advance of snowfall likely to be the signature event of a tenacious late-winter spell that has iced the region with record cold and nuisance storms.

"It's been horrendous," Steve Lorenz, the Philadelphia Streets Department chief engineer, said Wednesday as he was preparing his crews to do battle yet again, this time with up to eight inches of snow possible by day's end.

"In the last month, it feels like it's every other day," he said, adding that winter was making him a stranger in his household. "My kids introduce themselves to me every time I go home."

The National Weather Service in Mount Holly posted a winter-storm warning until 7 p.m. Thursday for four to eight inches of snow throughout the region, followed by another arctic invasion, with record low temperatures possible Friday morning.

Mayor Nutter declared a snow emergency for Philadelphia starting at 6 a.m. Thursday. Cars must be cleared from designated snow emergency routes, and scheduled Thursday trash and recycling collections will be delayed a week.

If it arrives as predicted, the storm would be the biggest snowfall of the season. Almost as if to make up for lost time, since late January a persistent spell of wintry weather has left a legacy of compacted ice on sidewalks and streets, busy emergency rooms, and well-mined salt domes.

As of Tuesday, the winter of 2014-15 in the Philadelphia region ranked second for salt use, at 142,965 tons, in the 33 years of records kept by the Pennsylvania Department of Transportation, said spokesman Gene Blaum.

In Philadelphia, it is No. 4, Lorenz said.

All that for just 15.5 inches of snow, according to official measurements. However, that snow has occurred on 16 different days, Blaum said.

Since Jan. 26, when the cold spell took hold, freezing rain or sleet has fallen at least seven times, adding to the ice woes, said Gary Szatkowski, meteorologist in charge of the Mount Holly office. The ice is so thick, he said, "you could do a snow archaeology."

The muck has been cemented on sun-deprived Philadelphia streets and elsewhere by almost unrelenting cold that has chilled the East. In February, abnormal cold covered just about all of eastern North America, from the Arctic to the Gulf of Mexico, according to NASA satellite data.

In Philadelphia, the last two weeks of February were the coldest such stretch in 141 years of government record-keeping. Since Jan. 26, temperatures have averaged 26.7 degrees in Philadelphia, close to nine below normal, with temperatures failing to go below freezing on only one of those days.

Emergency rooms in the region have seen brisk traffic, the result of ice slips or car accidents, hospital officials said.

"We have been very busy," said Michael H. Goodyear, chief of emergency medicine at Riddle Hospital in Delaware County, part of the system that includes Lankenau Medical Center, Bryn Mawr Hospital, and Paoli Hospital. "It's been lots of fender benders, and a ton of slip-and-falls, it seems."

Forecasters said Wednesday they were confident that the ice finally will disappear - under several inches of snow.

The weather service said five inches would be the minimum in the immediate Philadelphia area by the time the snow stops Thursday. At least 250 Thursday flights to and from Philadelphia International Airport had already been canceled Wednesday evening, representing about 20 percent of all arrivals and departures, according to airport spokeswoman Mary Flannery.

Temperatures are due to tumble Friday morning to near or below the record of 10 degrees, set in 1978, and flirt with the 1960 record of 9 on Saturday morning.

The equinox, however, will occur on schedule, and meteorologists say temperatures should punch into the 50s next week.

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Philly.com staff writer Emily Babay contributed to this article.