Just Like That, Two Big March Vermont Snowstorms Have Increased Spring Flood Threat

Snow-laden trees and deep snow this week around
St. Albans, Vermont.  A now much deeper snowpack
has somewhat increased the risk of spring flooding.

 Lo and behold, after pretty much an entire winter in which the snow pack in Vermont was well below average, the snow is now deep just as we're on the cusp of spring. 

That extra snow increases the flood threat in the coming weeks, but something like that is fortunately far from guaranteed.  It's still worth keeping an eye out on, though.  

The National Weather Service in South Burlington releases a winter and spring flood potential statement every other Thursday. Conveniently, the latest came just after the much larger of the two March snowstorms ended. 

Thursday's statement says the flood potential in northern and central Vermont is about normal. But it cautioned we'll have to start carefully watching weather patterns starting in about a week and a half. 

The amount of snow on the ground across Vermont - and the water in it - is now in many places above normal for this time of year.

The snow depth just below summit level on Mount Mansfield was  62 inches on Monday, just slightly below normal By Wednesday afternoon, the snow depth on the mountain had ballooned to 90 inches, which is roughly 15 inches above normal for the date.  

The snow water equivalent - the amount of "rain" available from the water in the snow and ice covering the ground is about 1.5 to 4 inches in the valleys, and four to eight inches at elevations between 1,500 and 2,500 feet.  I saw one measurement from Shrewsbury that showed 5.03 inches of "rain" locked up in the snowpack there. 

This week's snowstorm added one to three inches of snow water equivalent to the snowpack. Isolated areas in the high country of far southern Vermont added four inches of "rain" to the snow pack.

The snow cover in January and the first half of February was practically non-existent in Vermont. But much of the snow that has fallen since mid-February is still on the ground despite generally above average temperatures. That is in part because most of the above average temperatures have happened at night. Daytime readings have been closer to normal. So that limited much thawing so far. 

WHAT'S COMING

If you get the wrong kind of weather, that's a recipe for flooding.  The "wrong" weather is a sudden shift to much above normal temperatures combined with heavy rainfall.  

Jackson the Weather Dog is dwarfed by the big snow banks
he's inspecting for spring flood potential around
our house in St. Albans, Vermont. 

In the short term, that won't be a problem. Some light snow Thursday added a little tiny bit of potential flood water to the snow. 

Light rain causes some snow melt on Friday.  I noticed brooks and rivers rose somewhat with the thawing and rain, but nothing came close to flooding. And there's plenty of snow left to melt. 

A quick blast of chilly air will dump another dusting of snow in the valleys and a few inches in the central and northern Green Mountains. Again, just another small installment into the spring run-off potential from the mountains. 

Most of next week will have great sugaring weather, with highs near 40 and lows in the 20s. Great sugaring weather is also great flood prevention weather. A little snow melts each day, then things freeze up each night, so runoff isn't a problem.

Beyond that, it's beginning to look like we'll have a turn toward milder weather. The first shot at any spring flooding this year might be next weekend,  depending on the strength and path of the next storm system.  That storm is nearly a week away, so we don't know if it will be a warm, heavy rain, which would cause problem, or something more along the lines of what we had Friday, which wasn't at all scary.  

Even if the storm a week from now is warm and wet - again far from guaranteed - there will be plenty of snow left at mid-elevations and mountains to cause potential problems heading into April. Again, only if those spring rainstorms turn out to be hefty and drenching. 

Lake Champlain's lake level later this spring has gotten potentially more interesting, too. The lake level is around 96.4 feet, which is just slightly higher than normal for this time of year. 

Now, a lot of water has the potential to enter the lake from the surrounding countryside and mountains.  Especially if we have a lot of rain between now and May. 

Flood stage on the lake is 100 feet. I think we have a pretty good chance of achieving that. But minor flooding like that isn't a big problem. It's when we get up to 101 feet or so when trouble really begins. At this point, I don't think that will happen, but it is possible in a sort of low chance kind of way.

Whether we see any flooding this spring or not, I'm sure a lot of people will be relieved to see the snow banks around their homes gradually shrink and fade away under the warming rays of the sun.