Only three weeks after some states in the Northeast were enjoying record-high temperatures, residents in the region had to get out all of the deep-freeze gear Friday — hats, scarves, gloves, and even face masks — as they braved some of the coldest temperatures felt there all winter.

Temperatures will warm slightly Saturday before another blast of arctic air arrives in the region Monday, according to Accuweather.com. But before relief comes, the combination of a dip in the jet stream, the arctic air and biting northwest winds will create dangerously low temperatures.

At 7 a.m., it was four degrees at Boston's Logan Airport with a wind chill index of 16 below zero. At Worcester Regional Airport, it was even colder — with a temperature of three-below and a wind chill of 21 below. And in the city of Pittsfield, it was 6 below at 7 a.m. with a wind chill of 21 below.

The entire state of Massachusetts was under a wind chill advisory posted by the National Weather Service. Experts warned that the cold can be extremely dangerous to anyone not dressed properly.

Three inbound trains on one of the city's commuter rail line were delayed up to 15 minutes due to weather-related problems. Forecasters expecting a high of only 9 degrees in Worcester. Some recovery will occur over the weekend, with temperatures back in the 30s by Sunday.

In New York City, early morning temperatures Friday plummeted to 9 degrees, the coldest experienced since Jan. 28, 2005.

With the temperature in Central Park at 12 degrees, city officials on Friday declared a cold weather emergency that allows police to force homeless New Yorkers off the streets to save their lives.

"Though we haven't had much snow, winter has finally showed its nasty bite," said the Web site of the New York City Rescue Mission in Manhattan.

By midday, the city received nearly 2,000 calls from people complaining they had no heat or hot water.

The strong winds blowing across the warm waters of the Great Lakes Thursday produced heavy lake-effect snow squall, according to Accuweather.com.

And in Maine, the temperature dipped to zero or colder from Kittery to Fort Kent early Friday. In Portland, it was the coldest weather in nearly two years. Accuweather.com said temperatures in Greenville Friday morning bottomed out at 35 below zero.

The mercury dipped to 3 below zero in Portland, according to Michael Cempa of the National Weather Service office in Gray, Maine. The last time the temperature dipped below zero in Maine's largest city was on Jan. 29, 2005, when it was 5 below in Portland.

But it was much colder in northern Maine, where it dipped to minus 15 in Caribou, Houlton and Presque Isle, officials said. With gusting winds, the wind chill was expected to be nearly 40 below Friday afternoon in northern Maine.

But Cempa said that by Saturday, temperatures will be in the 20s in southern Maine.

In Pennsylvania, schools delayed openings so students would not have to wait for their school buses in the early morning cold.

About 50 vehicles including an ambulance piled up in a massive chain-reaction crash in a snowstorm on Interstate 90 in Erie, Pa., Thursday, killing one motorist and shutting down the highway for nearly 15 hours, officials said. Snowy conditions were also being blamed for another northwestern Pennsylvania crash that killed two teenagers.

The Associated Press contributed to this report.