National Weather Service meteorologists eyeballing Hurricane Sandy now are looking at a 21-hour window of mayhem for all of Western New York, with strong winds and saturated ground combining to topple trees, block roadways and take out power lines.

Water surges along Lake Ontario and Lake Erie also are anticipated.

The latest high-wind warning went into effect at 5 p.m. and remains until 2 p.m. Tuesday for all of Western New York.

As most of Western New York braced for the spin-off effects of Hurricane Sandy, consequences already were being felt, with about half of today’s flights already canceled at Buffalo Niagara International Airport.

But it will be hours until anybody learns how extensive any power outages might be.

The remnants of Hurricane Sandy will bring an unusual guest to Western New York – northerly winds, rather than the usual southwest or west.

“There definitely are going to be issues with power,” National Weather Service meteorologist Jim Mitchell said. “We’ve never seen winds from the north, northeasterly direction at this speed. We’ve never seen this before.”

Forecasters are calling for sustained north winds of up to 40 mph, with gusts up to 65 mph. Those speeds, while high, usually aren’t enough to create major headaches.

But there are two additional factors that will make things worse this time.

The first is the saturated ground, from the persistent rain that has pelted the area throughout the last few days.

Equally important is the wind direction that makes our trees more vulnerable to winds from the north or northeast, as opposed to the normal southwest or west.

“Their root structure, by its nature, is stronger on the west side of the trees, to anchor them in better,” Mitchell explained. “Some of them actually tilt slightly to the east, due to the sustained westerly winds. So they’re built to withstand the west wind. The way they’re anchored, the north and east sides of the trees aren’t as strong.”

The National Weather Service issued the high-wind warnings, even though the projected winds speeds barely qualified for those warnings.

Mitchell cited the damage left here in August 2011 by Tropical Storm Irene, which ushered in lighter winds than are expected in this storm.

“We were getting sub-warning winds that were taking down trees,” he said.

As of shortly after noon today, the airport reported 56 out of about 110 daily flights already canceled today.

“We’re still flying to Lauderdale and Atlanta, and everything west is leaving on time and coming in,” said C. Douglas Hartmayer, Niagara Frontier Transportation Authority director of public affairs. As expected, the cancellations have been concentrated in the flights to and from the New York City airports, Newark, Boston, Philadelphia, Baltimore and Washington.

Details on any disruptions in Metro Bus service later today and Tuesday can be found on the website, Hartmayer said.

During a briefing on the storm today, Mayor Byron W. Brown said the city does not anticipate moving Halloween trick-or-treating away from Wednesday night.

Brown also doesn’t think the city will issue any travel advisories, but warned drivers that the strongest winds are predicted from 8 tonight to 2 a.m. Tuesday.

He also urged residents to bring in patio furniture or Halloween decorations that could blow away in the wind.

City crews are out clearing storm drains, and the presence of leaves on the trees could make damage from the storm worse, said Public Works Commissioner Steven J. Stepniak.

Brown warned residents to stay away from power lines that have fallen to the ground and to treat them as if they are electrified. He also advised motorists to abide by all road closures.

Parking rules in the city have not changed, though city parking enforcement will use “common sense,” said Parking Commissioner Kevin Helfer.

Meanwhile, schools, colleges and many civic organizations are beginning to cancel events for tonight and Tuesday, including Buffalo State College canceling all evening classes and events beginning at 4:30 p.m. or later today. A decision on Tuesday classes will be posted on the Buffalo State website between 5 and 6 a.m. Tuesday.

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