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| Flooding in Richmond, Vermont, December 19, 2023, Heavy rain and warm temperatures in December made groundwater sopping wet, but got rid of most of Vermont's mountain snow cover. As things stand now that leaves this spring's flood potential as "normal" But a LOT can happen to change that one way or another by March and April |
Yeah, it's a little early to worry about spring floods, but I guess these early outlooks give us a baseline to start following trends.
A lot can happen between now and spring to affect our chances of yet another unwelcome inundation around Vermont when it warms up in a few months. But it's OK to keep tabs.
For the record, the outlook issued last Thursday for spring flooding works out to normal, all things considered. As you are probably well aware, December in Vermont was sopping wet, so groundwater is definitely above average.
However, snow cover was far below average when the flood forecast was issued last week, so there's not a lot of moisture built up in the mountains to unleash as floodwater when temperatures rise in March and April.
That's one of the big wild cards, though. We know snow cover will increase this month from the paltry levels we saw last week. Snow cover has already gone up in the past week, and might tonight. But it's still well below normal. However, if the rest of the winter proves snowy, which is actually possible, that would change the outlook.
Longer range forecasts indicate that starting about next Sunday, a new somewhat colder, and maybe (or maybe not!) somewhat drier weather pattern will take hold. I don't know if that will last all winter, or just be a brief blip, or something in between. If it does hold for the rest of the winter, chances are snow cover will finally build up in the mountains.
Which is one of the many reasons forecasting spring flooding is difficult to say the least in early January.
Ice jams are a big hazard with spring floods in Vermont. River ice can get pretty thick during colder winters, If a thaw breaks up that ice, those big chunks of ice can get stuck at barriers like bridges, creating a dam that results in a nasty upstream flood.
After the flooding and extraordinary warmth of December, there's almost no ice on Vermont rivers. So there's obviously no immediate threat of ice jams.
River ice will form as we get through January, but we don't know how thick it will get. Depends upon how cold it gets. The thicker the river ice, the greater the chances of ice jams that hold in place. Thinner ice breaks up into more small, slushy chunks that doesn't jam up so easily.
In the immediate future, over the next week or so, it's generally expected to be warmer and wetter than normal in Vermont. As mentioned this morning, there is some threat of flooding with our storm tonight and tomorrow, but mostly in far southern Vermont.
It's too soon to say whether the large storm expected Saturday will be warm and wet enough to create a flood threat. After that, as mentioned, a cooler, somewhat drier trend is expected to take over.
Another interesting wildcard is the Lake Champlain water level. It's much above normal for this time of year - only about half a foot below record highs for January. It has started to recede a bit from its late December peak though.
The lake level will probably take another bump upward after the storm tonight and tomorrow, and another one expected on Saturday. After that, the lake will probably slowly recede during the rest of January and February, unless it stays oddly warm and rainy. ss it's especially warm and rainy.
Still, if lake levels are still above normal in the spring, and there's a lot of snow that somehow accumulates in the mountains by then, we could have some real problems along the shores of Lake Champlain. Especially if it's also a rainy spring.
At this point, I'd say the risk is still low, but you never know.
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