Friday, April 4, 2014

Northern New England Flood Threat Continues For The Next Few Weeks

The deep, late winter snow on the ground is finally starting to melt across northern New York, and in Vermont, New Hampshire and Maine, which means now we have to start watching out for flooding.
Spring flooding near Enosburg, Vermont in
April, 2011. Similar scenes are possible
in northern New England over the next
few weeks.  

The National Weather Service in South Burlington, Vermont did its biweekly flood potential update last evening, and meteorologists there continue to say there's an above normal risk of spring flooding in the region.

And if flooding happens, it could easily occur starting now and the risk would continue for  at least the rest of the month.

At first, the biggest threat is ice jams, as some rivers, particularly more to the north, have thick ice on them. It's going to rain tonight, and again early next week, and that might be enough to start moving the ice and forming ice jams.

(And yes, there is a winter weather advisory up for tonight for most of central and eastern Vermont because of the risk of freezing rain and sleet, but it's still going to rain, too)

Ice jams can form quickly, and flooding behind those jams can form quickly, so be on the alert, starting tomorrow for this risk.

Another rain storm is due early next week, which could also set off the ice jams and low land flooding.

If we get a big period of very warm weather and heavy rain, it would combine with snow melt from the hills and mountains to contribute to some potentially nasty river flooding.

Don't let the bare spots in the snow on valley floors fool you. There's plenty of water locked up in the snow in the woods, and if you go up in elevation only a tiny bit, you get even more water locked up in deep snow.

In the Champlain Valley, there's up to four inches of rain within the remaining snow, says the National Weather Service. At elevations of between 1,000 and 2,500 feet, theres four to eight inches of rain locked up in the snow pack.

If flooding happens in Lake Champlain, and minor flooding is a good bet, it won't happen for awhile yet. In the past week, the lake level has risen from 94.9 feet above sea level to 95.66 feet. So the rise has started, but we've got a long way to go before the lake reaches minor flood stage, which is 100 feet.

It's still, of course impossible to say whether we will get much flooding. The weather pattern for most of the rest of April looks cool, which would be good because we'd get a gradual snow melt to minimize the flood risk.

On the other hand, the weather pattern looks like it will be active, with a parade of mid-sized rain storms, which might raise the flood risk.  Long range forecasts indicate the region will get one to two inches of rain, total, over the next week or so, which would be somewhat wetter than normal.

And there's no telling if one of these storms in the parade of systems might drop an unusually heavy amount of rain, or squirt a shot of very warm air into Vermont. That would be the worst case scenario for flooding.

So, if you live in a flood prone spot, there's no guarantee you'll get high water, but I'd prepare for it, just to be on the safe side.

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