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Coming warm-up to cause flooding

Don’t expect a “lake-effect tsunami” this weekend when temperatures soar into the 50s.

Given the unpredictable wildness of this week’s weather, though – who can really tell?

One thing is for sure, there will be some flooding.

The extent and exact locations around Western New York probably won’t be known until later today or Saturday.

“We don’t know, to be honest,” said Jon Hitchcock, meteorologist with the National Weather Service.

Residents in areas under as much as 2 to 3 feet of snow now could see grass again by next week, Hitchcock said.

Forecast models show temperatures will go above freezing to near 40 degrees Saturday and stay there through the nighttime hours before climbing to 50 degrees Sunday with chances for rainshowers throughout that period. Showers are likely Sunday night with temperatures remaining in the upper 40s before the mercury jumps even farther Monday – close to 60 degrees.

Shortly after 7 p.m. Thursday, the focus shifted from the unremitting heavy lake-effect snow to impending threats of flooding when the weather service issued a flood watch for Erie, Genesee and Wyoming counties with a special emphasis on “the Buffalo metro area.”

The watch runs from Sunday afternoon through Wednesday morning and states that “smaller streams and creeks will be prone to flooding from snow melt,” including those flowing through the city and its metropolitan area. Some of those include Tonawanda, Ellicott, Buffalo, Cayuga, Cazenovia and Cattaraugus creeks.

The statement said there’s a potential for “urban flooding” from the melting snow in towns where a lot of snow fell this week.

“A rule of thumb is that for every 10 inches of snow you get an inch of water, but this has been a heavy snow,” said Joseph Atkinson, an engineering professor who teaches hydrology at the University at Buffalo. “If we have 6 feet of snow – that’s 72 inches – that’s like 7 inches of rainfall.”

Hitchcock said weather service scientists will be out performing “snow core” tests throughout the region today to get a clearer picture of what the flooding could look like.

Scientists use cylindrical tubes to extract a core sample from the snow pack and then melt it down to determine the heaviness or concentration of water in the snow. It’s a process that’s very common in places with deep snow like the Colorado Rocky Mountain range or California’s Sierra Nevada region, but is pretty unusual for Western New York.

“When we have an idea how much water is in the snow, we’ll have a better idea how much water there will be,” Hitchcock said.

Once they obtain that data, weather service forecasters can plug it into computer models with hopes of getting an idea where waters will be rising and how quickly.

For officials and residents in places like the Village of Williamsville, the sooner the better.

“It’s a little bit of a nail-biter,” said Williamsville Mayor Brian Kulpa. “There isn’t a ton you can do.”

But the village is doing anything it can before the weekend, Kulpa said.

That has included removing fallen tree branches and other debris from Ellicott Creek, which runs through the village. On Wednesday, village officials removed three gates to a dam in the creek near Island Park and expect to take more of the gates out Saturday, Kulpa said.

Village officials also are asking residents to clear any street storm sewer drains of debris where possible as well as make preparations inside their homes for rising waters such as getting valuable items off of their basement floors, rolling up carpets and not making illegal sump pump connections to sanitary sewer lines.

The village also was working Thursday to run down a quantity of sandbags, Kulpa said. Usually, it obtains them from Erie County, the mayor noted, but county crews have been busy handling snow-related emergencies this week.

“We’re just trying to take these precautions,” Kulpa said.

Clarence is another community bracing for flooding, according to David Bissonette, the town’s disaster coordinator, who said the issue has been a major piece of discussion this week with other managers at Erie County’s emergency command center.

“We have already begun plans to monitor and prepare for the potential for flooding,” Bissonette said. “It’s been a big focus.”

“The way that water finds the storm sewers and creeks and streams in the area – that’s the next big phase.”

The weather service flood watch suggests the snow pack “stores a large quantity of water” and that combining the warmer temperatures, forecasted rain, “a southerly breeze and rising dew points” all will provide “a more efficient melting of the snowpack.”

“At first, the snowpack will absorb much of the water from the snow melt,” the weather service stated. “However, as the snowpack ripens – and with the addition of a half-inch or so of rainfall Sunday night and Monday – the potential for flooding will rapidly increase.”

The melted snow will find its way into one of two places – the ground or over land.

“You can have light snow and heavy snow. If this is heavy snow, that means there’s more water. That’s going to be a big issue,” said Chris Lowry, an assistant professor and hydrogeologist at UB. “When this snow melts and the rains comes, the ground won’t be able to absorb it fast enough.”

Because of the massive snowpack – of historic proportions – it could be anyone’s guess as to how bad the flooding is next week.

“We’re going into unknown territory,” Lowry said.

Here’s what to expect through early next week:

Saturday

The mercury crests above freezing for the first time since Monday, but a forecast high of 39 degrees is still 6 degrees cooler than average for the date. Still, with south winds up to 20 mph and a quarter-inch or more of rain forecast, some early melting of the snowpack is possible.

Sunday

This is when the thaw really kicks in. The flood watch starts at 1 p.m. Cloudy conditions with a daytime high near 50 degrees and a chance for rain will start knocking down the high piles of snow. A breezy Sunday night with rain and temperatures remaining near 50 degrees will continue the meltdown.

Monday

The thermometer creeps close to 60 degrees. Breezy conditions with rain is likely to speed the melting process. This is the day that officials like Bissonette fear most in places like Clarence where melting snow from upstream creeks begin their quick downstream flow. Showers also are likely Monday night, forecasters project, but the temperature will dip back into the low 40s.

Next two days

Rain is also possible during the day Tuesday as temperatures remain in the low 40s. Then rain and snow showers are possible by Tuesday night with lows around freezing. Wednesday’s high is projected to be 36 degrees under mostly cloudy conditions and the National Weather Service flood watch is scheduled to finally expire at 7 a.m.

email: tpignataro@buffnews.com