LOWELL -- Check your thermometers -- forecasters said a slight difference in temperature will determine whether Greater Lowell wake up Thursday in a winter wonderland or is just all wet.

The nor'easter that entered the area Wednesday night was expected to bring about a foot of snow to western parts of the state, but a warm, westward wind off the ocean will leave coastal communities with rain.

And Greater Lowell is right where the dividing line between snow and rain will likely be.

Meteorologist Matthew Belk, of the National Weather Service in Taunton, said there will be a big difference in snowfall totals between towns where overnight temperatures stay above freezing -- 32 degrees Fahrenheit -- and those where temperatures dip below that figure.

While forecasters can tell reasonably well where a storm will go, determining exactly what temperatures will be can be a much more difficult science, Belk said.

"You're only talking one degree, and to try to be that precise over such a large area is extremely difficult to do," he said. "It doesn't give you much wiggle room."

Areas in Worcester County and Northern Middlesex County communities such as Townsend can expect 8 to 12 inches of snow by the time this storm is over, while the National Weather Service is calling for just 2 to 4 inches in Bedford.

Bostonians should expect all rain.

Belk said some areas of ocean water are still 48 degrees to 50 degrees, and air above the ocean will be about 40 degrees as the nor'easter arrives. A strong wind blowing east will push much of that warmer air inland, leaving coastal areas with mostly rain.

But how far inland those warm winds will reach remains to be seen.

In the Midwest on Wednesday, hundreds of flights were canceled or delayed, scores of motorists got stuck on icy roads or slid into drifts, and blizzard warnings were issued amid snowy gusts of 30 mph that blanketed roads and windshields, at times causing whiteout conditions.



The Associated Press contributed to this report.