Saturday, April 18, 2015

Meltdown: Flood-potential update

Eroding snow pack still full of juice, but major, widespread floods unlikely.

Meltdown: Flood-potential update

As of 8 a.m. today, the mass of snow-and-ice that is oozing away still was holding more than a month’s worth of precipitation throughout Bucks and Montgomery Counties and part of Chester County.

Given the forecast, some nuisance flooding is all but a certainty on Friday, but despite all that water, and the extensive ice on rivers and streams, it appears that the region is going to dodge anything catastrophic.

The February sun, feeling more of its oats by the day, is likely to squeeze out some more water from the snow-and-ice pack this afternoon.

And rising dew points, along with fog tonight, will have consumed more of the snow and ice by the time any rain arrives.

Rain, perhaps even a thunderstorm, is forecast to continue until about noon tomorrow, but forecast rainfall amounts – around a half inch -- are well below the National Weather Service flood triggers, which range from 1.2 to 2.6 inches.

What’s more, rivers and streams remain well below flood stage. The Delaware River at Trenton was at 12.1 this morning; flood stage is 20. The Schuylkill at Norristown stood at 8.67; flood stage is 17, according to the U.S. Geological Survey.

“It doesn’t look like any are forecast to go to flood,” said Valerie Meola at the National Weather Service Office in Mount Holly.

River ice, however, is a wild card, as Ray Kruzdlo, hydrologist at the Mount Holly office, pointed out in the daily discussions.

When it breaks loose it can cause jamming, particularly near bends in rivers and streams, and that can result in backup flooding on one side of the jam, and flooding on the other side when the water breaks through.

One almost sure bet tomorrow will be road-ponding, with snow and ice clogging storm drains. Water can accumulate in a hurry on paved surfaces.

After the rain stops, gentle melting should resume, at least until Monday.

At this time, in the interests of regional sanity, we will eschew any discussion of the forecast for the rest of next week.

Inquirer Weather Columnist
About this blog

Everyone talks about the weather, and here we write about it.

When we’re around and conditions warrant, we’ll keep you updated about what’s coming, but we will do our best always to discuss weather and climate developments in context and remind you that nothing in the atmosphere happens in a vacuum.

Tony Wood has been writing about the atmosphere for The Inquirer for 26 years.

Reach Tony at twood@phillynews.com.

Tony Wood Inquirer Weather Columnist
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