Are Pennsylvania Ice Jams A Glimpse Of Vermont's Early Spring Future?

An ice jam in Swanton, Vermont after a rainy, warm
January thaw in 2018. This will be the first early
spring in a few years in which ice jams are
a real concern However, there's no
evidence that there's anything imminent. 

 Rain and a spring thaw in parts of Pennsylvania last week caused several potential dangerous ice jams.

Luckily, the Pennsylvania jams either broke up fast enough to prevent serious damage or hit in rural areas where there was little to damage. But those jams last week prompted some flash floods warnings and evacuations. 

It was a reminder, though, that a winter with lots of cold and snow can really create trouble when the spring thaw arrives in earnest. 

The same thing could happen here in Vermont later this spring. 

After a bitterly cold late January and early February. the weather abruptly turned in western Pennsylvania last Thursday and Friday. Thunderstorms dumped bursts of heavy rain on that region last night. By noon Friday, Pittsburgh's temperature was up to 63 degrees. 

That kind of late winter weather is a recipe for ice jams. Thick ice on rivers broke up in that weather, and the chunks of ice got stuck on river beds, bridge abutments and other obstacles. 

 It has temporarily gotten colder in Pennsylvania, so the risk of ice jam floods has eased. But if there are still frozen waterways there or anywhere else, there's a risk of ice jam floods as we head toward spring.

"Anywhere else" includes here in Vermont.

Pennsylvania's experience makes me wonder what might happen in Vermont later this spring. Ice on the rivers is thicker than it's been in years. There's a fair amount of snow on the ground ready to melt.

No real thaws or heavy rain is in the forecast. But a little more snow is in the pipeline. Thankfully no big storms, though. The later we get into March without a thaw, the more likely the weather could change abruptly to something warm and rainy. Which would set us up for ice jams. 

As prepped as Vermont seems for ice jam floods, we have a more than decent chance of avoiding trouble. In Vermont's history, we've had winters that were much colder, much snowier and much icier than this one. After most of those winters, the spring melt was gradual enough to only give us the usual minor spring lowland flooding. 

I'm only bringing this up because this is the first winter we've had in awhile in which river ice has gotten thick enough to build strong ice jams if the weather is right for them. 

To avoid trouble, we'll want perfect sugaring weather. That means mild, thawing afternoon and chilly subfreezing nights with only light precipitation. Under those conditions, the snow and ice softens and  gradually melt. . 

If we have a sudden, rainy warmup later in March, and the ice jams do develop, we can still be just fine.

Much like in Pennsylvania, our ice chunks under this fast thaw scenario would get hung up on river bends and other obstacles. The ice jam would then create flooding just upstream fro where the stuck ice is.  

Where these ice jams set up would spell the difference between slight inconveniences and real trouble. The unlikely but worst case scenario would be an ice jam just downstream from Montpelier. That would back the water up into the downtown, like it did so devastatingly in 1992.

Since Montpelier is to some extent recovering from the even worse July, 2023 flood, we don't need that. 

Bottom line: Don't panic, since there's absolutely no reason to. Instead just be aware if we have a spell of warm, rainy weather coming up over the next month.