I’m going to guess it has to do with how quickly the temperature change occurs, or other environmental factors prior to the freeze. It seems to be a somewhat rare occurrence, even in places where it gets very cold

It was raining here two weeks ago. Temperatures were in the 20-30s earlier this week. It’s being far below freezing AND recent warm weather that’s the danger.

It isn’t common, and explode is an exaggeration for what I have seen - just cracked bark (though the crack was probably abrupt and loud). Montana gets some every now and again, so I am guessing at least some parts of Alberta do too. Nobody has made a big deal about it in the past outside of folks interested in trees. This is some weird media hype.

The use of the word “explode” is misleading. It’s definitely misinformation.

Here’s an arborist talking about it, but basically:

Trees move sap and other liquids up and down their trunk from the soil underneath regularly. For trees like maples, this is where maple syrup comes from, except you have to collect a lot of sap and reduce it down to syrup.

The arborist claims that these liquids present in the tree when the temperature swings faster than the tree can respond expand due to freezing, which buckles tree trunks causing the outer bark to crack open and separate. The cracks can be from the ground up, or they can look like gashes in the side of the tree. There’s moisture in the soil too, which can shift tree roots and cause similar cracking.

People say “explode” because there’s usually a popping sound when this happens.

In other contexts, people call this frost upheave. Engineers know about this phenomenon, and try to bury equipment like pipes and cable and conduit below the frost line so frost upheave doesn’t crack and break that stuff. With trees, this frost upheave just takes place inside the trees themselves.

The trees don’t “explode” but young spindly trees can shatter if the conditions are just right, (and they are not right now). It’s very rare to have happen.

Source: I live in northern Minnesota. And I live closer to Winnipeg than the Twin cities.

People look at me funny when I tell them I used to have exploding head syndrome.

20° is close to the temperature where it doesn’t matter

For native animals? Probably not that many, as they are adapted to the fact that it gets very cold.

Stray cats and dogs? Probably quite a few.

This is exactly what came to mind for me as well! My second grade teacher read this and Hatchet to us. I remember him trying to figure out if it was from stray bullets from a hunter’s gun or what was going on.

Triggered the same memory for me, though I couldn’t remember the title. Just reserved a copy of the audiobook on Libby. Thanks!

The United States is very big. If you’re from a smaller country (particularly if it’s smaller east-to-west), it can be a little bit hard to comprehend how different the weather can be from one part of the country to another. While the weather does typically travel from West to East, it can change significantly along the way, and it usually takes several days to get from one coast to the other.

The highlighted area on the map is a massive region, wider than France and Germany put together (though much less populated). In fact, it’s quite rare for even this much of the country to have the same weather pattern. The simplest answer to why trees to the east and west are safe is that it’s not as cold there.

There are some other factors, too: just past the Western edge of the highlighted region are the Rocky Mountains, which significantly change weather patterns. The highlighted region consists of remarkably flat land (leveled by glacial action), meaning that there’s not much to break the wind as it sucks away the heat from the trees. To the East if this highlighted region are the Great Lakes, which also change weather patterns.

But the biggest answer is, it’s just not as cold there. Cleveland, OH (at a similar latitude, but further to the East) is going to be almost 20°F warmer than this (which is still bone-chilling, but not tree-exploding), and Boise, ID (similar latitude but to the West) is going to be almost 40°F warmer (practically tropical! /s).

Total guess, but: Lake effect probably prevents huge temperature swings further east (the great lakes are GIGANTIC sinks of energy), and there are mountains to the west, I believe. The problem is the flat area pictured.

Also, the shape of the polar vortex wind mass isn’t uniform, so it likely dips further south in that region than others (in part due to the barriers described above)

It’s also worth noting, if you’re not familiar with the US map, that the city of Minneapolis (where the anti-ICE protests are happening right now) is right about where the bottom of the “R” in “TREE” is on this map.

And well, ice.