How much of an inversion layer at around 700mb can different types of lift overcome?

[Rob H]

What would you like explained? I did mention in one of my previous posts on this thread that DVA can be used to infer where a cap may be removed via large-scale ascent. Was there something else?

Well... looking at this thing again:

Let's start with the basics. "Differential" I'm assuming is the physics use where you have things rotating at different velocities. "Vorticity" is just a measure of flow, and is very loosely the "spin" of the atmosphere. "Advection" means that this vorticity is moving somewhere. Right? Correct me on anything that's wrong, I have literally 0 college-level met training.

Then, Positive Vorticity Advection is where vorticity is increasing, which leads to upper divergence. This upper divergence is what lifts the air below it, so gives you the steeper lapse rates and expansion cooling that you mentioned before.

The green shaded areas on this map are where vorticity currently is. Are the X's vort maxes, or where vorticity is highest in a local area? Then the red lines would be negative vorticity advection, and the blue lines positive vorticity advection? I'm noticing that area of +10 PVA is coincidentally where the mesoanalysis CINH was decreased and near where storms fired. Does this mean that you probably don't want to be sitting under negative VA (red lines) on a chase day where the cap is your biggest problem?

If all this is accurate, and please correct me if I'm wrong, then the DVA map doesn't really explain why the 700mb temps lowered in that area, which I think you were kind of expressing that it didn't make sense. Maybe this is all just too complicated for someone like me, and I should just stick to 700mb temps/LSI and roll the dice when it looks close

That would get carried on through future cycles. However, with the other special observations that trickle in through the intermediate hours (after 12Z), maybe some of those observations indicated it was actually cooler at 700 mb than the forecasts had predicted. Therefore, the observations augment the background forecast by cooling off the temperatures somewhat, and this then carries on into future forecast cycles.

This is kind of the meat of what I was getting at. Maybe they got some sort of feedback between 18z and 23z that said "woah, 700mb temps should be a little cooler in this area". Could've been a special sounding, data from a commercial flight, or something along those lines? And this would likely be automated ingestion as opposed to someone manually tweaking grid values?

I guess the final question to tie all this together and get back to the OP's question - given X PVA value, are there any guidelines for inferring 700mb temp or CINH reduction? Based on the images above, it looks like the answer is not simple, and figuring cap erosion is better left to computers.

 

[Paul Townsend]

Hey Rob, in this case differential refers to the difference between the top and the bottom of the layer, of the parameter in question. Or, in other words, the positive vorticity advection at H4 minus the positive vorticity advection at H7. And better yet, the integral of said layer. Rising motion is the result of an increase with height of positive vorticity advection (or a decrease in negative vorticity advection with height but that is not what we find happening in the severe weather scenarios for which we are fond of looking). And then you couple that rising motion with what Jeff said about a layer having potential instability (high relative humidity at the bottom and low at the top) and you get the cap lifting and temperature cooling by expansion.

Often you will see in AFDs that they use DCVA. This is referring to this differential cyclonic vorticity advection. Cyclonic and positve being interchangable. Since windspeeds are higher aloft than near the surface, in regions where the vorticity is being advected from higher into lower values (cyclonic or positive vorticity advection), and windspeed is a part of the advection term, the use of differential is sometimes not used since it is assumed that the higher up PVA is greater than the PVA nearer to the surface.

In the map you provided, the shaded part is the vorticity at H5. The red dashed contours are where the motion is sinking (negative DPVA) and the blue solid contours are where there is rising motion (positive DPVA). Yes, the Xs are maxima in vorticity at H5.