How Do Those Things Form?
(scroll down for your Lowell weather update)
As promised, here is my Part 2 on tornadoes. This is national severe weather safety week, so I felt it might be appropriate to talk about what actually causes a tornado. Curious? Read on....
shot of a very wide tornado.... they can sometimes be up to a mile in diameter!
This is a "wall cloud" in a thunderstorm, associated with a strong, rotating updraft. These structures are usually a precursor to tornadoes - if you see one approaching, take cover!
Another large tornado. Note the dust and debris at the bottom of the funnel.
Tornadoes frequently "rope out" or become elongated and twisted before dissipating. The funnel size can decrease from hundreds of yards to only a few feet during this stage. Although it doesn't look as formidable as some of the other twisters above, they can still be deadly.So how does it all start?
The sun warms the grounds surface, creating plumes of hot air or thermals which rise through the colder atmosphere. As the plume of air cools, the water vapor in it condenses, forming clouds. Often, meteorologists refer to air "parcels," which is akin to thinking of the air as if it were in a balloon, and following that balloon through the atmosphere. It's easier to calculate and conceptualize than if we assume all air simply dispersed as it rose from the ground.
If atmospheric conditions are unstable enough, a tornadic thunderstorm may develop. If the rising parcel of air as described above remains warmer than the surrounding air, it will continue to rise, because warm air is less dense (and therefore lighter) than cold air. With the continued rising, cloud tops may reach 70,000 feet high in the atmosphere.
Strong thunderstorms like the one above are usually caused by approaching cold fronts. The cold, dense air rushing into the warmer, moister air, causes the warm air ahead of the front to rise, resulting in convective clouds and thunderstorms.
So what specifically causes a tornado?
There is still research being done regarding tornado formation, but the best known theory is that WIND SHEAR is the major component in creating tornadoes. So what's wind shear? Wind shear is when winds do not blow uniformly in one direction at the same speed. Wind shear can occur in a couple of different ways - the first, is when winds are blowing in the same direction, but at different speeds (refer to diagram below). The second is when winds are blowing at the same speeds, but with different directions with height (for example, winds near the ground might be blowing from the Southwest, but may be blowing from the North higher up in the atmosphere). The third form of wind shear is a messy combo of the two - Winds can blow at different speeds, at different directions, at different heights. Following along so far? Then continue on below....
The varying wind speeds can cause a rotating cylinder of air in the atmosphere. For example, what would happen if you pushed on the top of a ball? It would roll. The shearing mechanism above works in the same way. The winds are stronger higher up than they are closer to the ground, causes the air to "roll" in a cylinder.
Now I'll put it all together for you
The sun warms the grounds surface, creating plumes of hot air or thermals which rise through the colder atmosphere. As the plume of air cools, the water vapor in it condenses, forming clouds. Often, meteorologists refer to air "parcels," which is akin to thinking of the air as if it were in a balloon, and following that balloon through the atmosphere. It's easier to calculate and conceptualize than if we assume all air simply dispersed as it rose from the ground.
If atmospheric conditions are unstable enough, a tornadic thunderstorm may develop. If the rising parcel of air as described above remains warmer than the surrounding air, it will continue to rise, because warm air is less dense (and therefore lighter) than cold air. With the continued rising, cloud tops may reach 70,000 feet high in the atmosphere.
Strong thunderstorms like the one above are usually caused by approaching cold fronts. The cold, dense air rushing into the warmer, moister air, causes the warm air ahead of the front to rise, resulting in convective clouds and thunderstorms.
So what specifically causes a tornado?
There is still research being done regarding tornado formation, but the best known theory is that WIND SHEAR is the major component in creating tornadoes. So what's wind shear? Wind shear is when winds do not blow uniformly in one direction at the same speed. Wind shear can occur in a couple of different ways - the first, is when winds are blowing in the same direction, but at different speeds (refer to diagram below). The second is when winds are blowing at the same speeds, but with different directions with height (for example, winds near the ground might be blowing from the Southwest, but may be blowing from the North higher up in the atmosphere). The third form of wind shear is a messy combo of the two - Winds can blow at different speeds, at different directions, at different heights. Following along so far? Then continue on below....
The varying wind speeds can cause a rotating cylinder of air in the atmosphere. For example, what would happen if you pushed on the top of a ball? It would roll. The shearing mechanism above works in the same way. The winds are stronger higher up than they are closer to the ground, causes the air to "roll" in a cylinder.
Now I'll put it all together for you
(or try anyway!)
Clouds have those "thermals" as I mentioned above. They are usually referred to as updrafts in thunderstorms, as they are much stronger. Air can rise up into the storm at speeds of 60 mph or more!
Once that updraft rushes up into the atmosphere and hits that rolling cylinder of air, it causes the tornado. How, you ask? What would happen if you were holding a long piece of ribbon horizontally just above the floor, and then someone else poked the center of that ribbon with their finger? It wouldn't stay flat, would it. The harder your friend pokes the ribbon, the taller the ribbon will become, until eventually the ribbon is no longer horizontal, but vertical!
That's what happens with the tornado. The rapidly rising air in the updraft distorts the horizontally rolling cylinder of air until it is no longer parallel to the ground high up in the air, but perpendicular to it, extending from the cloud to the ground's surface. And when that happens, you have the birth of a tornado. Look out!
So, there's my attempt to explain a pretty technical process. Still have questions? Shoot me an email..... I'll be more than happy to respond.
And now for Lowell Weather
High pressure over the region today will slide east as a storm system currently centered over Missouri tracks our way for Friday. That means enjoy today, because tomorrow looks to be a wet one with rain during the day, with a possible embedded thunderstorm and highs in the lower 50s. Yet another system looks to approach the area Saturday with some more showers, although it will be warmer with highs in the mid 60s.
There are currently flood watches in effect for most of New Hampshire and Maine because of these systems. Although the probably won't dump a ton of water over New England, major rivers are still high after the last Nor'easter. It won't take too much rain to see them rise again. So for people in Lowell, keep an eye on the Merrimack, as it may begin to rise yet again this weekend as the runoff from smaller streams drains into the river system.
At this time, it doesn't look to be anything close to another Mother's Day flooding event, just a rise of a couple feet or so. If this changes, the WUML weather team will be sure to let you know.
And finally, for all Umass Lowell Students, tomorrow is the spring carnival! If you plan on attending, you may want to wear a waterproof coat. Also, feel free to stop by the WUML 91.5 FM booth, as we will be broadcasting LIVE all day from the carnival. Ask a weather question, say hello, or meet the crew of the Campus Buzz News Team.
Until next time, this Umass Lowell Student Meteorologist John Webster.
Clouds have those "thermals" as I mentioned above. They are usually referred to as updrafts in thunderstorms, as they are much stronger. Air can rise up into the storm at speeds of 60 mph or more!
Once that updraft rushes up into the atmosphere and hits that rolling cylinder of air, it causes the tornado. How, you ask? What would happen if you were holding a long piece of ribbon horizontally just above the floor, and then someone else poked the center of that ribbon with their finger? It wouldn't stay flat, would it. The harder your friend pokes the ribbon, the taller the ribbon will become, until eventually the ribbon is no longer horizontal, but vertical!
That's what happens with the tornado. The rapidly rising air in the updraft distorts the horizontally rolling cylinder of air until it is no longer parallel to the ground high up in the air, but perpendicular to it, extending from the cloud to the ground's surface. And when that happens, you have the birth of a tornado. Look out!
So, there's my attempt to explain a pretty technical process. Still have questions? Shoot me an email..... I'll be more than happy to respond.
And now for Lowell Weather
High pressure over the region today will slide east as a storm system currently centered over Missouri tracks our way for Friday. That means enjoy today, because tomorrow looks to be a wet one with rain during the day, with a possible embedded thunderstorm and highs in the lower 50s. Yet another system looks to approach the area Saturday with some more showers, although it will be warmer with highs in the mid 60s.
There are currently flood watches in effect for most of New Hampshire and Maine because of these systems. Although the probably won't dump a ton of water over New England, major rivers are still high after the last Nor'easter. It won't take too much rain to see them rise again. So for people in Lowell, keep an eye on the Merrimack, as it may begin to rise yet again this weekend as the runoff from smaller streams drains into the river system.
At this time, it doesn't look to be anything close to another Mother's Day flooding event, just a rise of a couple feet or so. If this changes, the WUML weather team will be sure to let you know.
And finally, for all Umass Lowell Students, tomorrow is the spring carnival! If you plan on attending, you may want to wear a waterproof coat. Also, feel free to stop by the WUML 91.5 FM booth, as we will be broadcasting LIVE all day from the carnival. Ask a weather question, say hello, or meet the crew of the Campus Buzz News Team.
Until next time, this Umass Lowell Student Meteorologist John Webster.
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