 |
| Motorists slog through spring floodwaters near Enosburg, Vermont in April, 2011. |
At the moment, there are plenty of mixed signals on what kind of spring flooding, if any, the Green Mountain State sees this year.
First, some background. Flooding can and does occur at any time of year in Vermont. Ice jams during rainy, very warm January thaws can trigger floods, as they did in 2018.
Late spring and summer torrential thunderstorms can set off big local flash floods, as they have in many years, like in 2013. Tropical storms heading north into New England we know can cause serious floods, as we remember from Irene in 2011.
Large autumn storms can sweep through and cause floods, as we saw big time last Halloween. And of course, rain and melting snow can cause spring flooding in March and April.
Quite frankly, Vermont doesn't need any more flooding. Last April, the kind of spring flood I'm talking about hit parts of central, southern and eastern Vermont, prompting a federal disaster declaration.
Then that even worse Halloween storm a few months back triggered serious flooding across the northern half of Vermont, prompting another federal disaster declaration. Yep, two such declarations within about seven months.
So, on to this spring. We might as well talk about it today, Sunday, since the outdoors does have a mild, spring-like feel.
Today's weather signals that we are now entering our first good thaw of late winter and early spring. The first chance of any late winter or spring flooding comes late this week, but that is decidedly iffy. The chances that an expected pretty big storm late this week are pretty low.
That's because at this point, the storm looks like it will bring us a mix of stuff. It will probably include rain, but that rain will likely mostly just soak into the existing snowpack. Plus the storm will probably bring other types of precipitation, like wet snow, sleet and/or freezing rain. If the storm ends up being mostly snow or mixed precipitation, that would actually add slightly to the risk of flooding later.
That's because there will be even more snow and ice locked up on the ground, waiting to melt.
Even if that happens, the amount of snow on the ground, and the amount of water locked up in that snow, is roughly normal for this time of year, says the National Weather Service South Burlington.
That NWS office issues a winter/spring flood outlook every other week this time of year, so that's where I'm getting this information. A normal late winter snowpack implies a normal spring flooding season, if you ignore all other possible factors, which of course you can't do.
Moisture in the soil is near to just a little above normal, which is largely a legacy of last year's very wet autumn. River flows currently are also near or a little above normal. There's ice in the rivers which could cause ice jams, but it's not a huge amount of ice. We've had a warm winter.
Lake Champlain also has a near normal level heading into the spring flood season.
All this means is it's a tossup as to whether you should think about any spring flooding in Vermont this year.
Spring flooding is a major concern for much of the nation this year.
Last spring brought widespread, disastrous and in some places unprecedented flooding to much of the central United States, especially in places like South Dakota, Nebraska, Iowa and Missouri.
The outlook for this year is pretty grim, especially in the eastern Dakotas, the upper half of the Mississippi Valley, around the Great Lakes and other parts of the Midwest, as The Weather Channel reports. Of course, we've already had super serious flooding in the South this month.
In the bigger river systems like the Missouri, Mississippi, Ohio and other large rivers, you can make an educated guess ahead of time as to how serious flooding might be a month or two down the road,
Vermont lacks those big rivers. In the large river systems further west, floods are slow rolling disasters. Vermont floods are like a mugging. They hit you in an instant, and just as quickly, they're gone. It's hard to predict a mugger, and it's hard to predict a Vermont flood well in advance.
In some years, when the snowpack and the soil moisture and the rivers are high in late February, you can safely anticipate at least some flooding later in the spring. In normal-ish years like this, it all depends on what March and early April does.
If we have a lot of very wet storms over the next two months - either rain or snow - that can make the flooding risk skyrocket. If we have a March and early April full of perfect sugaring weather - mild thawing afternoons and freezing nights - the snow melt is slow and we have a low flood risk. A big bout of super warm, record temperatures, especially if accompanied by heavy rain, you get floods.
Long range forecasts are tricky, but some of those forecasts do predict a relatively stormy first half of March. Beyond that, you might as well flip a coin.
Climate change adds an additional twist. The risk of heavier individual rain storms is getting higher. However, that overall risk is a big picture thing. You really can't tell when those bigger, heavier storms might hit. The next monster storm could be next week, or it could wait five years or more. Who knows?
The only thing I can say is have your sump pumps ready, just in case. This year truly is a tossup.
No comments:
Post a Comment