Closed Lows & cut-off Lows

[Jared Farrer]

I wanted to ask in the advanced so I could get a more advanced topic going.

What is the difference between a Closed upper level low and a normal low? Whats the significance there? In other words when a low closes off whats happening, and what should one expect? From a Meteorology perspective and a chasing, severe weather perspective.

The other part of my question is cut-off lows. Same goes.

 

[Peter Wharton]

Here's a link to start the explanation process:

Closed low - http://www.theweatherprediction.com/habyhints/200/

Cutoff low - scroll down on the page - "cutoff low is a special case of a closed low"

 

[Jared Farrer]

So are closed upper level lows always vertically stacked? And it mentions its basically an occluded low, which suggests upper level cold air being wrapped all the way around it. Whats that mean from a chasing stand point? Haby suggests its a bad thing for severe weather. Can anyone go into detail?

 

[Tim Vasquez]

Closed lows are not always vertically stacked. Last weekend's blizzard in the southern Plains was a good example of that. It was baroclinic and exhibited significant tilt, but the upper low was closed.

Tim

 

[Derrick Herndon]

As Tim already stated closed lows do not necessarily mean vertically stacked but there is a tendency for them to move in that direction. In fact many extratropical cyclones reach their strongest intensity, lowest pressure, shortly after the 500 mb low closes off, prior to the system becoming stacked.

From a chasing standpoint the occlusion process means the best surface based instability will be shifted into the narrowing warm sector. Convection along the occlusion will have a tendency to be elevated in nature. The tendency for the low to become vertically stacked will also decrease shear, especially directional shear.

So are closed upper level lows always vertically stacked? And it mentions its basically an occluded low, which suggests upper level cold air being wrapped all the way around it. Whats that mean from a chasing stand point? Haby suggests its a bad thing for severe weather. Can anyone go into detail?

 

[Jared Farrer]

As Tim already stated closed lows do not necessarily mean vertically stacked but there is a tendency for them to move in that direction. In fact many extratropical cyclones reach their strongest intensity, lowest pressure, shortly after the 500 mb low closes off, prior to the system becoming stacked.

From a chasing standpoint the occlusion process means the best surface based instability will be shifted into the narrowing warm sector. Convection along the occlusion will have a tendency to be elevated in nature. The tendency for the low to become vertically stacked will also decrease shear, especially directional shear.

When you say the occlusion process and narrowing warm sector, it sounds like your talking about the occlusion process of a surface low.

What mechanisms are responsible for closing the low off? Is it just the fact cold air is being pulled in around the low. And correct me if I am wrong but low tilt is a function of baroclinicity is it not. Larger temp contrasts in and around the lows causes the tilting with height towards the colder air. Barotropic systems have less of a temp contrast in and around them? That would explain why tropical systems are mostly barotropic. And Cold core setups are for the most part barotropic?