The GOES-East weather satellite peers down at an intense band of lake-effect snow east of Lake Ontario on Friday. (RAMMB/CIRA)

A prolific lake-effect snow band is raging in Upstate New York, producing whiteout conditions, furious winds and mind-boggling snow accumulations in a razor-thin band.

Thirty inches had already fallen in localized areas by midmorning Friday, with up to 20 inches more in some locales a distinct possibility. Thunder and lightning were ricocheting throughout the thumping band of powder, punctuating the extreme conditions that could last through late Friday night.

Some 28.5 inches had been measured in Copenhagen, N.Y., as of 9 a.m. Friday, with the snow falling in barely 25 hours with rates at times nearing 4 inches per hour. Copenhagen is about 15 miles east-southeast of Watertown on the eastern shores of Lake Ontario.

The GOES-East weather satellite captures the band of lake-effect snow from sunrise through early afternoon Friday. (College of DuPage/NOAA)

“With Copenhagen, that’s just overnight,” said Aaron Reynolds, a meteorologist with the National Weather Service in Buffalo. “They could have more than that right now.”

Watertown itself had a reading of 28.3 inches as of midday Friday. Overnight, 17.1 inches was recorded just south of town, while east of the city had picked up eight inches. Snowfall amounts can vary wildly in lake-effect snow environments. Carthage had about two feet.

Meanwhile, the National Weather Service is forecasting another 12 to 18 inches in spots through Friday evening, with a touch more possible during the overnight. It’s not out of the question that one small area winds up with a four-foot jackpot of snow.

The blizzard is the product of a perfect recipe for lake-effect snow production. Strong west-southwesterly winds blowing down the length of the lake scoop up readily available moisture. Bitterly cold air just above the surface allows air in contact with the lake to rise. And abnormally low ice cover on the Great Lakes has exposed the above-freezing water to juice up the air above, allowing the lake-effect “machine” to efficiently convert Great Lakes moisture into piles of snow.

Winds gusted to 56 mph in Watertown on Thursday afternoon and continued to gust over 40 mph much of Thursday night.

For a location to meet blizzard criteria, it must record sustained winds or frequent gusts at or above 35 mph for at least three consecutive hours, coincident with considerable falling or blowing snow reducing visibility below a quarter mile. Watertown has recorded those conditions for 15 hours since Thursday, with up to six hours consecutively.

At 3 a.m. Friday, the airport’s observation was “thunderstorm in vicinity, light snow, and breezy.” More than a dozen cloud-to-ground lightning strikes have been detected within the lake-effect band.

The main lake-effect snow band was only 18 miles wide Friday afternoon. The band is expected to remain roughly in place through mid- to late evening before a change in wind direction shoves it to the south and east. Until then, Reynolds says, another 12 to 18 inches is “easily” possible, with a few four-foot snow totals “not out of the question.”

Intense lake-effect bands are generally more common at the start of the season over Lake Erie; in November 2014, some places near Buffalo picked up seven feet of snow in roughly a week.

The lake effect can occasionally continue even into February or March off Lake Ontario. That’s thanks to the lake’s depth.

“Lake Ontario is a very, very deep lake,” Reynolds explained. “It doesn’t freeze over like Lake Erie does. I can’t remember the last time … there was ice at the center of the lake.”

The National Weather Service's original forecast for hefty lake-effect snow through Saturday called for as much as 40 inches. That number will probably be beaten. (WeatherBell)

Once the snow finally comes to an end, the concern will pivot to inland flooding. Temperatures next week will warm into the mid- to upper 40s, with rain in the forecast by Monday. A freshly fallen and rapidly melting snowpack absorbing rainwater generally sets the stage for river flooding.

“Up in there, they have the Black River Valley near the Tug Hill [Plateau],” Reynolds explained. “You get some rain, it’s not a good combination. It tends to cause some problems with flooding.”

His office is hoping for a slow “melt-off,” but only time will tell.