Tuesday, March 18, 2014

Never Ending Winter Could Come With A Hangover: Floods Are A Threat

Tuesday morning, it was below zero across much of northern New York and northern New England.  Winter storm warnings were up for parts of Minnesota and northern Wisconsin, areas of the country already deep in snow.  
Severe flooding along Lake Champlain in
Colchester, Vermont, May, 2011. Although
I don't expect it to get this bad in 2014,
some spring flooding looks more likely as winter
drags on and snow and ice still accumulate.  

I don't see any real breaks in the cold in the Great Lakes region and Northeastern United States through the end of March. It'll keep snowing in the region occasionally, too, ensuring the snow cover lasts and lasts.

Winter is hanging on.

When, and if, winter does break, we could suffer from a hangover of sorts in the form of spring flooding.

It's funny. In January, snow cover was below normal and the thought was then the spring flooding threat would be minimal.

Then the cold deepened and so did the snow in February. The spring flooding threat in most of these regions was upgraded to "normal" chances.

Now, with snow still deepening and cold hanging on, the threat of spring inundations seems to be growing.

There's certainly no guarantee of flooding once the spring thaw arrives. Or any flooding could turn out to be minor.

But there are reasons to be worried.

The snow is deep and has a lot of water content for this time of year in the Great Lakes region and northern New England, including here where I live in Vermont.

The snowcover isn't setting any records and is not as ominous as the big spring flood year of 2011, but it's still worth keeping an eye out on.

By my estimation, the highest chances of spring flooding are in the northern half of Minnesota, northern Wisconsin, the Upper Penninsula of Michigan, the northern half of New York, and in most of Vermont, New Hampshire and Maine.

The longer we go toward and into April, the greater the chances are that we get a sudden spike of temperatures way up into the 50s, 60s, and even 70s, accompanied by rain.

That would induce a lot of sudden melting and a rush of rain water and snowmelt from the mountains. The ground in most places is frozen hard, too, so don't count on much of that water harmlessly soaking into the soil.

An even bigger threat is ice jams.  It's been very cold in the Midwest and Northeast, as you are well aware.   Ice is thick on a lot of rivers, and record cold temperatures this past week have thickened the ice even more. It's going to be cold next week, too.

The thicker the river ice, the more likely chunks of it will form jams when a thaw and more runoff finally arrive.  There's also old ice jams frozen in place in the Midwest and Northeast from brief thaws earlier this winter. That could lead to even more flood trouble.

Back in 2011, an hugely snowy winter followed by what was easily the wettest spring on record unleashed a lot of flooding in Vermont and surrounding areas. Lake Champlain had a record, lengthy and costly flood.

Water rose to unprecedented levels. The water and battering waves damaged or destroyed hundreds, if not thousands of camps and homes along the lake shores in Vermont, New York and Quebec.

I still don't believe Lake Champlain flooding will get nearly as bad as 2011. There's not as much snow to melt as there was in 2011. And the chances of another record wet spring are remote.

Still, I think at least minor Lake Champlain flooding,  when the lake level gets up to 100 feet above sea level is a pretty good bet toward May.

As I said, bigtime flooding is not guaranteed. In 2001, many feet of snow lay on the ground in western New England and northern New York as April arrived. This was after a record snowy March. The fear was all the snow would abruptly melt in the warm, rainy weather of April.

Instead, April that year was very dry, and frequent overnight freezes slowed runoff. There was only minor flooding and minor damage that year.

In 2014, we won't find out what will happen until, and if, winter ends.


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