When I was growing up in Nebraska, severe weather came with a cold front swept in from Canada or other parts north. The cold air lifted the warm, humid air and excitement ensued. Keep in mind, weather radar was just starting to come into use, and a lot of atmospheric science had yet to be discovered. I never heard of a “triple point.”
Then I moved to Texas.
A triple-point in meteorology is a low pressure system, dry-line, and cold front combination. That’s where the worst of our spring-summer severe weather comes from (blizzards are a little different).
The brown line is a dry line, dividing drier air from the southwest from the warm, humid air being pulled in by the low. The blue line is a cold-front, the red with rounded lumps is a warm front. Everything rotates counter-clockwise around the Lo. The Lo, or low pressure center, pulls the warm air and moisture up from the Gulf of Mexico. It also provides some of the energy needed for exciting weather.
You have warm moist air, dry air, cold air that lifts the warm, moist air, and the low pressure system to pull everything together. The results are often exciting. If you are a storm spotter or weather junkie, they are fun exciting. If you are in the way of the storm, or a major urban area, the excitement is more of the, “Oh nuts, not again, please go away, please line out, please dry line quickly come!” Supercells tend to form that the junction of the air masses, where you have fuel, lift, and unstable air with winds that are going in different directions at different elevations. Storms that do form explode up, shooting well into the atmosphere. As they climb, they start producing precipitation. Because the winds are at varying heights, the storms move and pull in more warm air while the cold air and rain/hail falls behind. This keeps the storm “alive” rather than choking itself with the cold downdraft.
The different wind layers inside the storm criss cross. That starts air rotating. All that is needed for a tornado at that point is an updraft to tip the rotation. The rotating air turns vertical. If it touches the ground, you have a tornado. The combination of warm air, dry air, cold air fuels the storm for hours.
What people on the ground hope for is for the storms to form a line along the dry line. When storms “line out,” they lose some of their individual punch and are less likely to drop tornadoes. However, they start moving as a group, and can “train”, dropping lots and lots of moisture over the same place as they go. They can also start moving faster and faster, bowing out and producing very strong winds ahead of themselves, even a derecho in extreme cases. A bow echo on radar means wind. Hook echo means tornado or really big hail. The taller the storm, the more likely you are to get big hail. As in cabbage-sized hail. Or grapefruit (1-2 pounds). This falls from the sky at about 60 miles per hour. It will kill you.
So when we on the Great Plains and High Plains see a triple-point forming, we brace for trouble. This area hasn’t seen conditions that ripe for severe tornadic storms for almost a decade. I’d just as soon wait that long again. Small tornadoes are not rare, but the big “It ate Oklahoma City/Xenia/Omaha!” size monsters generally stay to our east. But this is an El Niño year, and we are blessed with lots of moisture. Storms are the price we pay for the moisture.
I still don’t have to like them. I’ve been through three tornadoes. That’s more than enough, thanks.
For more discussion on the topic: https://stormtrack.org/community/threads/triple-point.17709/