(Updates flight cancellations, other details)
By Elizabeth Dilts and Scott Malone
NEW YORK/BOSTON, Jan 2 (Reuters) - The governors of New York and New Jersey declared a state of emergency and pleaded with residents to stay indoors on Thursday as a major snowstorm bore down on the northeastern United States, delaying or canceling thousands of flights.
The first major winter storm of 2014 brought bone-chilling temperatures and high winds from the lower Mississippi Valley to the Atlantic coast, with parts of New England, including Boston, bracing for up to 14 inches (36 cm) of snow by Friday morning.
"As this winter storm unfolds, bringing heavy snow and high winds to many parts of the state, I strongly urge all New Yorkers to exercise caution, avoid travel and stay indoors," New York Governor Andrew Cuomo said.
Amid flight cancellations that hit just as many travelers were returning from holiday breaks, officials at Boston's Logan International Airport said that up to a quarter of its scheduled flights had been canceled on Thursday afternoon and evening.
But Ed Freni, aviation director of Massport, the state agency that operates Logan, said that two runways remained open and that he expected the airport to continue operating as long as it was safe to do so.
Cuomo and New Jersey Governor Chris Christie both ordered state offices closed on Friday for non-essential employees, saying they expected the worst to hit between late Thursday and early Friday morning. The state of New Jersey said public schools would be closed in Hoboken and Jersey City on Friday.
"The real action is going to get cranked up this evening and during the overnight hours. We'll have heavy snow, windy conditions, reduced visibilities," said Kim Buttrick, a meteorologist with the National Weather Service in Taunton, Massachusetts.
DE BLASIO'S BIG TEST
The storm posed the first major challenge to New York's new mayor, Bill de Blasio. Problems from digging out from snowstorms have been political havoc for mayors in the United States' biggest city for decades.
After his first emergency management meeting, De Blasio pleaded with New Yorkers stay off the streets.
"This is the first of many times I will say please stay indoors. Stay out of your cars. If you don't need to go out, please don't go out," he said.
The powerful storm forced cancellation of nearly 2,500 U.S. flights with another 7,000 delayed. Chicago's O'Hare International and Newark's Liberty International Airport were hit the worst, according to FlightAware, a website that tracks air travel.
New York's three major airports were preparing to accommodate stranded travelers whose flights were canceled.
"We have a few hundred cots at each of the airports should you decide to become an overnight guest," said Thomas Bosco, an official with the Port Authority of New York and Jersey, at New York's LaGuardia Airport. The authority also runs Newark and John F. Kennedy International Airport.
Ruben Raskin of San Jose, California, who was in the Boston area visiting his girlfriend, worried that his Friday flight out of Logan could be delayed or canceled.
"It kind of reminds me why I moved to San Jose after going to college out here," said Raskin, 23.
Conditions in Boston were bad enough by afternoon that the "Frozen Fenway" winter carnival, featuring sledding and college ice-hockey at the baseball stadium where the Red Sox play, was canceled for Thursday and Friday.
TEMPERATURES TO PLUMMET
The weather service said the mass of Arctic air would drop temperatures to levels 20 to 30 degrees below normal, with record lows possible on Friday.
"Temperatures are expected to plummet tonight and tomorrow with wind chills dropping as low as 25 degrees below zero Fahrenheit (-32 Celsius)," said Massachusetts Governor Deval Patrick. "That is a very dangerous set of circumstances."
The low temperature in the contiguous United States on Wednesday was -47 Fahrenheit (-43 Celsius), reached in Van Buren, Maine, and tied in Babbitt and Embarrass, Minnesota, the weather service said.
Patrick told non-essential state workers to head home at 3 p.m. ET (2000 GMT) as did his counterparts in neighboring Connecticut.
Forecast snowfall varied widely, with Washington expected to see under an inch (2 cm), Philadelphia and New York 4 to 8 inches (10-20 cm), Hartford 6 to 10 inches (15-25 cm) and Boston 8 to 14 inches (20-36 cm).
But even before the worst of the storm hit slippery road conditions made driving a hazard in many storm-hit areas.
In Cleveland, Ohio, Chris Behm spent an hour trying to reach the vocational training center for developmentally disabled people where he works before calling the commute off and urging his 19 employees to stay home.
"It was terrible on all of the roads and there is more weather on its way," Behm said. "It just wasn't worth it to open and possibly kill someone."
Officials in Boston and Providence said schools would be closed on Friday, and in other districts throughout the region, parents were bracing for the possibility their children would be home on Friday.
"It's tough with these storms because I end up using days off that I don't want to take," said Kristen Carson, who had taken the train into Manhattan from her home in suburban Montclair, New Jersey. "After the holiday, it's really kind of a pinch." (Additional reporting by Victoria Cavaliere, Marina Lopes and Scott DiSavino in New York, Daniel Lovering in Cambridge, Massachusetts, Ian Simpson in Washington, Kim Palmer in Cleveland and Mary Wisniewski in Chicago; Writing by Scott Malone and Dan Whitcomb; Editing by Ken Wills)