Manchester has declared a snow emergency for tonight in advance of the impending winter storm.

The city's public works director, Kevin Sheppard, said no parking will be allowed on any city streets from 10 p.m. Wednesday to 6 a.m. on Thursday.

Any vehicle parked in violation of the snow emergency declaration will be towed and stored at the Derryfield Park lot off Bridge Street. Owners will be required to provide proof of ownership and pay a $110 fee. Vehicles not claimed within 24 hours are subject to further fees.

The city provides two locations for residents to park their vehicles during snow emergencies: the Victory parking garage at Chestnut and Amherst streets; and the Pearl Street parking lot.

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The first significant snowstorm of the season could dump 12 to 16 inches in some portions of New Hampshire, with the central part of the state getting the most snowfall, while the coast and southern New Hampshire could see a changeover to rain, the National Weather Service said.

A winter storm watch begins at 10 p.m. tonight and lasts until 4 a.m. Friday. Snow is expected to be heavy for most of the state, with somewhat smaller accumulations in Coos County, said Weather Service meteorologist Andy Pohl.

The more urban areas of the state — Manchester and Nashua — could see snow change over to mixed precipitation during the morning commute Thursday. Manchester expects 4 to 8 inches of snow before the changeover, said Manchester Public Works Director Kevin Sheppard, after consulting with the weather service the city uses.

Sleet, rain and freezing rain are all possible during the day, Sheppard said.

“(Thursday) will not be a fun day. This is one of those storms where we will have to prepare for the worst,” he said. Manchester and other cities have declared overnight parking bans.

Winds will be stronger at the coast — 25 to 35 mph, with 45 mph gusts. The slightly warmer temperatures at the coast will make for a wetter snow, he said. Wind and wet snow increase the likelihood of power failures, he warned.

Also, U.S. Airways announced Tuesday that it was waiving its $150 ticket change fee for travelers flying into or out of the Northeast and Midwest — including the Manchester and Portland airports — Wednesday and Thursday.

A midwestern snowstorm brought a white Christmas to areas such as Little Rock, Ark., and is advancing northward today, according to accuweather.com.

Bloomington, Ind., reported 11 1/2 inches of snow at 10:45 a.m. today. About the same time, freezing rain had converted to snow in Pittsburgh, Pa.; visibility there was less than a mile.

Pohl said the heaviest snowfall in New Hampshire could be in the foothills and southern mountains. The weather service said Laconia and Conway could receive 12 to 16 inches. Coos County could get between 8 and 12 inches.

Pohl said snow should start falling in southern New Hampshire between midnight and 4 a.m. Thursday. The heaviest snowfalls will be between 3 a.m. and 3 p.m. Thursday.

Unitil, which counts about 45,000 electricity customers in the New Hampshire Seacoast region, said it has secured third-party crews to provide help if needed.

“Wetter, stickier snow can have a greater impact on the system compared to the drier, fluffier stuff,” Unitil media relations manager Alec O'Meara said. “We will be carefully watching the consistency of the snow, the changeover to rain and forecasted wind speeds overnight and into tomorrow, and we will be prepared to address outages, should they occur.”

Public Service of New Hampshire said Wednesday that it was pre-staging its crews.

mhayward@unionleader.com